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Data Sets and Information
• data set : LRO DLRE 5 POLAR RESOURCE PRODUCT
  LRO DLRE PRP, thermal model fits to first mapping year Diviner polar observations
• data set : LRO DLRE 5 GRIDDED DATA RECORDS
  LRO DLRE GDR, Averaged reflectances, temperatures, and derived values.
• instrument : InSight Radiometer
  The InSight radiometer is associated with the Heat Flow and Physical Properties Package (HP3). It is designed to measurement surface temperature in support of HP3 in determining the subsurface temperature profile. The radiometer is mounted on the lander. It measures the radiative flux in three infrared bands.
• data set : FIELD EXP E RANGER II PLUS RDMT & THRM CALIB RDR TEMP V1.0
  The Directional Emissivity Archive contains calibrated reduced data records (RDRs) acquired using a radiometer and a thermistor during the earth-based 1989 Geologic Remote Sensing Field Experiment (GRSFE).
• instrument : NET FLUX RADIOMETER for GP
  Instrument Overview =================== The Galileo Probe Net Flux Radiometer (NFR) measured net and upward radiation fluxes in Jupiter's atmosphere between about 0.44 bars and 14 bars, using five spectral channels to separate solar and thermal components. The instrument used an optical head extending through the probe wall to obtain views of the Jovian atmosphere. It sampled upward and downward radiation fluxes with a single 40 degree (full angle) conical field of view chopped between directions +/- 45 degrees from horizontal. The NFR consists of two major sub-assemblies: the electronics module (EM), and optical head (OH). The electronics module is about 13 cm x 19.5 cm x 16 cm high, while the optical head is about 8.5 cm x 8 cm high x 10.5 cm long. The total weight of the NFR is 3.134 kg, of which the optical head is 0.672 kg. The electronics module has four feet which are bolted to the Probe instrument shelf. The optical head, supported only by its attachment to the electronics module, extends out of the Probe through the Probe thermal blanket and aeroshell to allow the NFR sensors to view atmospheric radiation. The instrument was built by Martin Marietta Astronautics Group. The principal investigator is Dr. Lawrence Sromovsky of the University of Wisconsin Space Science and Engineering Center. Scientific Objectives ===================== On December 7, 1995 the Galileo Probe Net Flux Radiometer made the first in-situ measurements of radiative fluxes within Jupiter's atmosphere. The instrument's first targets were the primary drives for atmospheric motions: absorbed solar radiation and the flux of energy from the planet's interior. Because solar radiation absorption and planetary emission occur at different places and altitudes, net radiative heating and cooling result in buoyancy differences that force atmospheric motions. An understanding of Jovian circulation thus requires knowledge of the vertical profile of radiative heating and cooling and its horizontal distribution as well. The NFR contributed to this understanding by measuring the difference between upward and downward radiation fluxes, the net flux, as a function of altitude during probe descent. Because the radiative power per unit area absorbed by an atmospheric layer is equal to the difference in net fluxes at the boundaries of the layer, the vertical derivative of the net flux defines the radiative energy absorbed per unit volume, and thus defines the radiative heating (or cooling) of the atmosphere. However, because the Galileo probe provided only one sample profile of Jovian atmospheric conditions at one location and time, it is especially important to understand why the measured radiative energy deposition occurs: we might then have some idea of how to apply the results to other atmospheric regions which were not samples. The NFR experiment contributes to understanding horizontal variations by making spectral measurements which illuminate the mechanisms by which radiation interacts with the atmosphere. Five broad spectral bands were used to separate the vertical distribution of radiative heating by sunlight and radiative cooling and heating by exchanges of thermal infrared radiation. The profiles of radiation flux also contain signatures of the substances that absorb and emit radiation - gases and particulates, and thus provide independent constraints on models of atmospheric composition and cloud structure. when these are interpreted with other probe measurements and linked with orbiter observations they provide a basis for using orbiter observations to extend radiative heating determinations to other locations on the planet. A full treatment of scientific objectives and results can be found in [SROMOVSKYETAL1998]. Preliminary scientific results were documented in [SROMOVSKYETAL1996]. Calibration =========== Calibration of the instrument was carried out at the University of Wisconsin. Details of calibration have been documented in [SROMOVSKYETAL1992] and [SROMOVSKY&FRY1994]. The calibration constants and algorithms used for the flight instrument can be found in [SROMOVSKYETAL1998]. Operational Considerations ========================== Several special factors affected the quality of data acquired during descent into Jupiter's atmosphere. Among them were temperatures outside the range of instrument calibration, and thermal perturbations which we were unable to duplicate in the laboratory. Details of our treatment of these factors can be found in [SROMOVSKYETAL1998]. Optical Head ============ The optical head contains a rotating optics assembly, support structure, apertures, reference blackbody sources and a position control system. The rotating assembly includes detectors, field-of-view shaping optics, and heated diamond window, all of which rotate as a unit between three different pairs of four distinct angular orientations. Because the rotating optics could not structurally support a high pressure differential, the interior of the rotating optics is designed to admit ambient external gas during descent. To inhibit possible condensation on interior optical surfaces, as flow into the rotor is controlled by vents within the electronics module and at the base of the rotor. These vents take advantage of the dynamic pressure distribution around the Galileo descent probe to constrain gas flow. Gas enters the probe through a large vent at the back (aft) of the probe. some of this gas enters the electronics module through a molecular sieve filter at the top of the electronics. The filtered gas, also warmed (in upper descent) or cooled (in lower descent) by the electronics module, enters the rear of the optical head through a vent at the base of the electronics module. From this point the gas flows partly into the rotor through the rotor base vent (near the rear bearing) and partly through the motor and rotor bearings into the forward part of the optical head and then through the apertures into the external atmosphere. The differential pressure driving this flow is approximately 1 mb and at 1 atmosphere the total flow rate through the optical head will be approximately 100 cc/sec. When the optical system is not viewing external radiation, it views one of two internal radiation sources: an ambient blackbody source which is thermally coupled to the wall of the front housing, and a heated blackbody source which is servo-controlled to a temperature of approximately 107 deg C (the servo point is attained in air or vacuum, but generally is not attained in He or H2 atmospheres where high gas conductivity limits the blackbody temperature to a maximum differential above the ambient atmospheric temperature). Detector Package ================ All NFR spectral channels use LiTaO3 pyroelectric thermal detectors to convert absorbed radiation power to electrical signals. The NFR detector package contains an array of six detectors mounted in close proximity on a single circuit board. Spectral filters are mounted in a filter frame which is hermetically sealed to the detector circuit board, trapping xenon gas in the volume between the detectors and the filter frame. (All channels experience additional spectral filtering by the 0.2 mm thick diamond window at the entrance to the rotating optics, the spectral reflectivity of the mirrors, and the spectral response of the detectors.) The backfill of the very heavy xenon gas is used to buffer the small amount of hydrogen gas which will diffuse into the detector package during descent. The buffering effect maintains low thermal conductivity inside the detector package and thereby eliminates significant thermal crosstalk which otherwise would occur via gas conduction between detector elements. There are two filter frames: an upper frame containing only a CaF2 long-wave blocker for channel C, and a lower filter frame containing five spectral filters and one opaque blocker for the blind channel. Each pyroelectric detector element consists of a crystal approximately 1 mm x 2 mm x 25 microns thick mounted on 0.015 inch high mesas made of a vibration dampening material called Visilox. Black paint (3M velvet) is applied to the top surface so as to cover the active (electroded) area but not the entire detector. The typical paint thickness is 20-25 microns. Detectors have a primary thermal time constant of approximately 110 ms, an electrical capacitance of about 40 pF, and a responsivity of approximately 1400 V/W. In the laboratory the dominant noise source is Johnson noise associated with the detector load resistor. Spectral Response ================= The NFR made measurements in five parallel spectral channels. Two solar channels provided complete integration of all solar wavelengths from 0.3-3.5 microns (B) and a red-weighted subset from 0.6-3.5 microns (E) in which methane absorption is most significant. A broadband thermal channel (A) from 3-200 microns measured sources and sinks of Jupiter's thermal radiation as a whole. Channel C (3.5-5.8 microns) sampled the narrow band 5-micron window in Jupiter's atmosphere where gaseous absorption is relatively low. Channel D (14-150 microns) sampled the hydrogen-dominated longwave region of the thermal spectrum. Channel F is a blind channel that measured non-radiative detector perturbations, needed to correct for similar perturbations in the other channels. None of the spectral channels has a flat responsivity, and thus energy deposition profiles and heating and cooling rates are somewhat model dependent. To compute a heating rate due to thermal radiation exchange requires a uniform weighting of the entire thermal spectrum. But since the spectrum isn't measured, we must integrate the spectral flux density of a model spectrum that leads to the same simulated NFR measurement. Electronics =========== The NFR electronics consist of: digital circuits, analog circuits (detector pre-amplifiers, post-amplifiers, demodulators and integrators), gain select amplifier, analog to digital converter, housekeeping monitors, motor driver, and optics position sensors. Digital Circuits ================ The microprocessor system consists of the 1802 CPU (Central Processing Unit), 256 words of RAM (Random Access Memory), 6144 8-bit words of PROM (Programmable Read-Only Memory), nine I/O (Input/Output) ports and a power-up reset circuit. The RAM is used to provide 256 bytes of temporary storage for data values during data accumulation and manipulation. The six 1-Kbyte PROMs contain the program necessary to operate the instrument. At any given time only one of the PROMs is turned on and for only 1 microsecond of the 8 microsecond machine cycle, providing a factor of 48 reduction of power consumption by the PROMs. Six 8-bit wide output ports are used to control the non-digital NFR subsystem. Three input ports are used to read data from the NFR subsystems. The 2048 Hz spacecraft clock is divided down to a 4-Hz signal which is used to interrupt the microprocessor. The Minor Frame signal from the spacecraft is used to synchronize the 4-Hz timer and also to synchronize the software with spacecraft timing. The software does not begin cycling in its normal mode until the microprocessor detects a Minor Frame interrupt. The PROM software controls the sequence, timing, and duration of motor control pulses. After each cycle of the optical rotor, position sensor phototransistors are read to determine if the optics are at the correct position. If any one of the 22 half cycles of one instrument cycle results in an incorrect optics position, the microprocessor notes this in the data stream by setting the motor position error bit to one for that IC. Analog Circuits =============== There are six channels of analog processors, one for each detector. Each channel includes a detector signal pre-amplifier, a post-amplifier, a demodulator and an integrator. This six pre-amplifiers are housed in a hybrid package placed adjacent to the detectors on the rotating optics. The rest of the analog circuits reside on two circuits boards within the electronics module. Pre-Amplifiers ============== Each pre-amplifier is a DC differential amplifier with a gain of 6.67, using U423 dual JFET inputs. The effective input load resistance of 0.909E+10 ohm (1E+10 ohm in parallel with 1E+11 ohm) in combination with the typical detector capacitance of 40 pF leads to a detector electrical droop time constant of 0.36 s. with this droop a typical detector will generate an electrical offset of 0.055 V per deg C per minute of thermal ramp. Because the load resistance is so much less than 1E+13 ohm detector resistance, detector noise is dominated by the Johnson noise of the load resistors (modified by the detector shunt capacitance, of course). Post-Amplifiers =============== The six parallel post-amplifiers each consists of three non-inverting amplifiers in series (except for channels B and E which have one inversion to compensate for an inversion built into the detector package). Single pole RC filters are used to block the DC component from the hybrid and to tailor the frequency response of the circuit. The filter components are chosen to give a maximum response at 16 Hz. This may seem strange in view of our fundamental 2-Hz detector signal. However, this filter function acts somewhat like a differentiator, which, in combination with the following integrator, results in a very small sensitivity to the details of signal transitions and a high sensitivity only to the final values attained after each flip of the rotor. This effect minimizes asymmetry errors. FET (Field Effect Transistor) switches at the input of each post- amplifier allow the inputs to be grounded through a 100 ohm resistor, providing a zero reading to be integrated as the Analog Zero (AZ) data. The AZ value is intended to be a measure of offset in the integration circuitry. The gain of the post amplifiers is tailored to the dynamic range expected from each channel. To extend the dynamic range of channels A, C, and D, which receive much stronger signals from the internal heated blackbody than they do from Jupiter's atmosphere (at least in laboratory situations), the third amplifiers of the circuits for those channels (and also for channel F) have two possible gains selectable with a FET switch. The gain is switched to 8 for analog zero, up flux, and net flux measurements, and switched to unity for the blackbody calibrate measurement. The solar channels, B and E, receive relatively weak signals from the on-board calibration source and thus do not need gain reduction capabilities. Demodulator and Integrator ========================== Each demodulator is a gain unity, reversible polarity amplifier, the polarity of which is controlled by two FET switches, synchronized to the 2-Hz NFR decommutation signal. The integrator consists of an inverting amplifier with a 0.82 microfarad capacitor in the feedback loop and a 1 megohm resistor connected between the output of the demodulator and the input to the integrating amplifier. A FET switch is placed in parallel with the capacitor to short out the charge after a measurement has been taken. Two other switches control input to the integrator. In one configuration the output of the demodulator is connected to the integrator (enabling integration); in the other configuration the demodulator output is disconnected and the integrator input is grounded (holding the integrated value for readout by the A/D converter). Gain Select Amplifier (GSA) =========================== All six integrator outputs and all housekeeping monitor outputs are routed by a 22-channel multiplexer to the gain selection circuits which properly scale those analog signals for input to the Analog to Digital Converter (ADC)described below. A 3-channel gain select multiplexer selects either the output of the 22-channel multiplexer or the output of one of two cascaded amplifiers, each with a gain of eight. The three multiplexed channels view the output of the 22-channel multiplexer at gains of 1, 8, and 64. Analog to Digital Converter (ADC) ================================= The ADC is a 12-bit, +10 to -10 V, successive approximation type converter, used over a +5 to -5 V 11-bit range only. The most significant bit (bit 11) indicates polarity of the signal, and the second most significant bit indicates a positive or negative overrange. Data reported to the Probe telemetry include the sign, two bits indicating the gain setting of the GSA, and nine bits of data from the ADC (bits 1 through 9 - bit zero is unused). The microprocessor changes the gain of the GSA as required to obtain an on-scale reading for the ADC. The GSA is first set to its maximum gain of 64. If the processor detects that the ADC is in an overrange condition (input greater than +5 or less than -5 V), it sets the GSA to a gain of 8. If this also leads to an overrange condition, the GSA is set to a gain of one. Housekeeping Monitors ===================== The following is a list of housekeeping data that the NFR reports in the probe telemetry stream: HB - Hot Blackbody Temp A1 - Ambient Wall Warm Temp A2 - Ambient Wall Cold Temp DT - Detector Temperature WT - Window Temperature ET - Electronics Temperature V1 - +10 Volt ADC Reference V2 - +7 Volt Supply BI - Hot BB Current WI - Window Heater Current G1 - GSA Cal for gain=1 G2 - GSA Zero for gain=1 G3 - GSA Cal for gain=8 G4 - GSA Zero for gain=8 G5 - GSA Cal for gain=64 G6 - GSA Zero for gain=64 The diode voltage drop change with temperature of a 1N4148 serves as the temperature sensor for the DT and ET temperature monitors. The HB, A1, A2 and WT temperature sensors are Fenwal GB38SM43 thermistors. The HB sensor is located on the back of the hot blackbody printed circuit resistor. The A1 and A2 thermistors are located in an aluminum mount on the ambient wall. The WT sensor is located in the window housing structure on the rotating optics. The DT sensing diode is mounted directly to the detector board on the rotating optics. Motor Driver ============ The motor driver is basically a pair of 28-V H-bridge circuits capable of driving up to 250 mA of reversible current through each of the two motor coils. The microprocessor controls the motor driver by writing a one into the appropriate latch bit to turn on one of two coils in one of two polarities. In addition to these four latch bits, there is one additional bit reserved for controlling eddy current damping by shorting one of the two coils. The exact time and duration of each motor coil pulse is controlled by the PROM software, and is tuned, prior to burning PROMs, to obtain stable symmetric optical head rotation characteristics. To obtain stable rotor motion characteristics under varying temperature conditions, the motor drive currents are stabilized by a current regulator circuit. Optics Position Sensors ======================= The rotor gear on the rotating optics has four slots cut into it so that four LED-photo transistor pairs mounted around the gear can determine if the rotor is at 0, 90, 180, or 270 degrees (+/- 5 deg). Only one photo- transistor will be turned on indicating the position of the rotor. If the correct transistor is not illuminated, this condition is reported in the data stream by setting the position error flag. Operating Modes =============== The detectors, field-of-view shaping optics, and heated diamond window all rotate as a unit between three different pairs of four distinct angular orientations. Besides the upward and downward viewing positions, there are two horizontal positions, one providing a view of an ambient blackbody, and the other providing a view of a heated blackbody reference, both blackbodies being located in opposite instrument walls. In the Net Flux (NF) Mode, the rotating optics chops between upward and downward views. In the Blackbody Calibrate (BC) Mode the FOV is chopped between the ambient and heated blackbody references. In Upflux Mode (UF), the FOV is chopped between the downward viewing direction and the ambient blackbody reference. Time-integrated measurements are returned every six seconds for all channels in parallel. During each 2-minute Data Cycle (DC) there are 20 Integration Cycles (IC) during which decommutated, filtered, and integrated signals are computed. Among these there are 17 cycles of net flux measurements, one upflux measurement, one blackbody calibration measurement, and one analog zero measurement. All chopping is at a 2-Hz rate, and the decommutated signal integration generally extends for 5.5 seconds (the first 11 of 12 cycles for each six seconds). The two net flux measurements following AZ and UF mode measurements (as well as AZ mode measurements themselves) are 'short-cycled', meaning that only the last five cycles are integrated, because of large DC level shifts after changing operating modes. Measured Parameters =================== The Net Flux Radiometer actually measures net radiance rather that net flux. This net radiance measurement is convoluted by the instrument field-of-view and the non-flat spectral response. A discussion of the relationship between measured net radiance and true net flux can be found in [SROMOVSKYETAL1998] and [SROMOVSKYETAL1992]. Timing ====== NFR data can be related to data from other probe instruments via the time after Minor Frame Zero. This parameter is included in all descent measurement files, for each data point.
• instrument : INFRARED THERMAL MAPPER for VO1
  INSTRUMENT: INFRARED THERMAL MAPPER SPACECRAFT: VIKING ORBITER 1 Instrument Information ====================== Instrument Id : IRTM Instrument Host Id : VO1 Pi Pds User Id : HKIEFFER Instrument Name : UNK Instrument Type : RADIOMETER Build Date : 1974 Instrument Mass : 8.400000 Instrument Length : 0.330000 Instrument Width : 0.267000 Instrument Height : 0.178000 Instrument Serial Number : 003 Instrument Manufacturer Name : SANTA BARBARA RESEARCH CENTER Instrument Description ====================== The IRTM contains four small Cassegrainian telescopes which each image the same, seven circular areas. There is a total of twenty-eight channels in four surface and one atmospheric thermal band from 6 micrometer to 30 micrometer and a broad solar reflectance band. All channels are sampled simultaneously, using the spacecraft scanning capability to map the radiance over small and large areas of the planet. All channels use thermopile detectors; spectral passbands are determined by a combination of interference filters, detector lens materials, antireflection coatings, and reststrahlen optics. The scan modes are described in the PDS INSTRUMENT MODE DESCRIPTION. Science Objectives ================== The objective of the Viking Orbiter infrared thermal mapper (IRTM) is to measure the thermal emission of the Martian surface and atmosphere and total reflected sunlight with high spatial and flux resolution. Operational Considerations ========================== Most low and moderate resolution IRTM data were acquired through using 'box scans'. These were commonly acquired between 1-6 hours from periapsis, and utilized the scan platform to slew back and forth in cone angle (in the direction the IRTM chevron points) with small offsets in the same direction between these oscillating slews. Ignoring spacecraft motion, this pattern would generate bi-directional evenly spaced scans with the seven IRTM detectors. Spacecraft motion during the scan sequence, typically of 10-40 minutes duration, created some distortion in this otherwise uniform pattern. Typical resulting scans across the planetary surface are shown in Figure 3 of Kieffer et al., 1976. These scans were usually designed to extend slightly off the limb of the planet on at least one side. These 'planet port' off-planet data provided the best estimates of the zero radiance response of the instrument. When the spacecraft was near periapsis, the apparent motion of the planetary surface relative to the spacecraft was too rapid to allow oscillating slews. At these times, the instrument would simply 'stare' in one direction and use the spacecraft motion to sweep the detector pattern across the surface. These observations were usually acquired in Normal Mode, but occasionally Fixed Planet was used. At irregular times through the mission, 'phase function' observations were made. These involved using the two axis scan platform to follow one point on the ground as the spacecraft went from horizon to horizon relative to this surface point. In actuality, this sequence was acquired using a small number of discrete scan platform moves, allowing the instrument to 'stare' across a short stripe centered on the target point between slews. Such 'phase function' observations typically yielded about 10 different viewing geometries within a single sequence. These observations were particularly useful in determining the influence of the atmosphere. In preparation of the IRTM data set, all observations which were more than 1 1/2 degrees apparent angle above the nearest limb of the planet were deleted. Geometry Errors Due to Uncertain Timing: Early and late during the Viking mission, orbital solutions based on the tracking telemetry were determined every few days. During VO-1 revolution 175-603 and VO-2 revolutions 118-521, orbital solutions were often separated by a week or more. Because there is significant irregularity in the Martian gravitional field, these irregularities could slowly influence the orbit of the Viking spacecraft in unpredictable ways. The primary influence was in the period of the orbit, resulting in uncertainty as to exactly where the spacecraft was along its orbit at any specific time. These uncertainties were as large as 75 seconds in the worst case. Far from periapsis, these timing uncertainties were not of major significance because the spacecraft velocities were low and the projected fields of views on the planet were large. However, near periapsis, the IRTM field of view could move across the surface equivalent to its full width in as little as one second. Thus, when there was a large timing error, the computed ground intercept locations could be in error by many fields of view. In the worst case, these positions may be in error by up to 200 km. When the magnitude of this problem was discovered, the SEDR (geometry calculations) for the imaging instrument was rerun with revised orbit solutions. However, it was impractical to regenerate the IRTM SEDR and these errors have not been corrected. There was an attempt by the navigational team to estimate the magnitude of the timing error for both Viking spacecraft for those revolutions through the affected part of the Viking mission. This is described in the 1980 April 14 memo by Frank Palluconi, which contains estimates of the magnitude of the error for each revolution. Hugh Kieffer has a copy (the sole surviving copy?) of this memo. A direct determination of the timing offset can be made from the IRTM data alone in those instances when thermal patterns can be unambiguously identified with surface features. Since the dominant geometric error is in time, maps of thermal patterns (typically as contours of observed temperature minus the calculated standard model temperature) can be slid across the cartographic map parallel to the subspacecraft track (if the instrument was in fixed planet mode, this is simply sliding the IRTM trace along its own path) until the thermal and cartographic features are aligned. Because there are small gaps in the IRTM coverage every 64 ICKs, the amount the IRTM pattern must be shifted to agree with the surface morphology can be scaled directly into a timing offset in seconds. This has been done for a variety of high resolution scans across Arsia Mons (by Jim Zimbelman) and for many scans across Valles Marineris (by David Paige and Hugh Kieffer). A set of known offsets is slowly accumulating. Hugh Kieffer has a copy (the sole surviving copy?) of the memo discussing this problem. Calibration Description ======================= Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the planet port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Telescope D channels were calibrated using a different method. The radiance source was a mercury-xenon lamp and narrowband filter centered at 0.896 micrometer with a bandwidth of 425 nm. The in-band radiance of the lamp was known by direct comparison with a standard lamp acquired from the National Bureau of Standards, using a silicon photodiode as a transfer standard. The relative spectral response measurements then allowed extension of the one-point absolute calibration to the entire passband. Gains for the D channels were set to give full scale for 75% of the diffuse reflection of solar irradiance at Mars average distance from the sun. Using integrals of the Planck function and the measured spectral response, the flux response of the IRTM is found to be close to linear in the thermal channels. The best fit quadratic functions, normalized to full scale, typically had constant and quadratic coefficients of 0.002 and 0.02, respectively. The solar band channels, which had much higher absolute flux levels at full scale, showed a decrease in response at high signal levels corresponding to a quadratic coefficient of 0.07. With the IRTM in the vacuum chamber, the instrument response was measured at four lamp currents. An additional series of wide band measurements utilizing a NBS standard lamp and a barium sulfate diffusing screen, in which only the lamp-screen distance was changed, was used to determine in detail the solar band nonlinearity. During spacecraft thermal-vacuum testing and in flight, a small drift of about 1-min duration was found to be induced when the scan mirror moved to the reference position in normal mode. This appears to be caused by the decrease in radiative heat loss from the instrument when the telescopes do not view space. The shape of this postreference drift was accurately determined during normal mode sequences when the spacecraft was well away from Mars, and this effect is removed in the data reduction. The change of the thermal state of the IRTM caused by large scan platform slew or planetary radiation near periapsis can introduce significant drifts of the zero-flux level. These shifts have a time constant of 1-2 min or longer, and their magnitude increases with inband wavelength and preamplifier gain. It is probably due primarily to very small temperature gradients induced in the detector packages as the general instrument temperature changes. A significant design feature of the IRTM is that the space DN level of each channel is measured immediately prior to and after the restore which occurs each minute in normal mode. A linear interpolation between these zero-flux DN levels is used in data decalibration. The remaining quadratic and higher order drift is generally negligible. Section 'IRTM' ============== Total Fovs : 7 Data Rate : 250.000000 Sample Bits : 10 'IRTM' Detectors ---------------- A 'IRTM' Electronics ------------------ IRTM 'IRTM' Filters -------------- SOLAR UV-22 T11 T15 T20 T7 T9 'IRTM' Section Optic IDs ------------------------ A B C D In modes -------- FIXED PLANET FIXED REFERENCE FIXED SPACE MODIFIED NORMAL NORMAL 'IRTM' Section FOV Shape 'CIRCULAR' ----------------------------------- Section Id : IRTM Fovs : 7 Horizontal Pixel Fov : 0.292000 Vertical Pixel Fov : 0.292000 Horizontal Fov : 2.402000 Vertical Fov : 1.347000 'IRTM' Section Parameter 'RADIANCE A' ------------------------------------- The A telescope measured wavelengths between 16 and 30 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE A Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.002030 Noise Level : 0.000001 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE B' ------------------------------------- The B telescope measured wavelengths between 10 and 13 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE B Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.003120 Noise Level : 0.000001 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE C1' -------------------------------------- The C1 set of 3 detectors (out of 7 in the C telescope) were limited by filtering to wavelengths between 6 and 8 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE C1 Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.003190 Noise Level : 0.000001 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE C2' -------------------------------------- The C2 set of 3 detectors (out of 7 in the C telescope) were limited by filtering to wavelengths between 8 and 10 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE C2 Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.001980 Noise Level : 0.000001 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE C3' -------------------------------------- The C3 detector/filter combination within the C telescope responded to wavelengths between 14.5 and 15.5 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE C3 Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.006340 Noise Level : 0.000003 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE D' ------------------------------------- The D telescope measured wavelengths between 0.3 and 3.0 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE D Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 135.840000 Noise Level : 0.030000 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND Instrument Detector 'A' ======================= Detector Type : THERMOPILE ARRAY Detector Aspect Ratio : 1.000000 Minimum Wavelength : 0.300000 Maximum Wavelength : 100.000000 Nominal Operating Temperature : 275.000000 Description ----------- The seven-element thin-film antimony-bismuth thermopile array used in the IRTM is shown in Fig. 7 of CHASE_ETAL_1978. The chevron arrangement was based on the need for uniform coverage irrespective of scan platform orientation; it also allowed the detectors to all be approximately the same distance from the telescope optic axis. In this application thermopiles were found to be better than other thermal detectors because they operate to dc and exhibit no 1/f noise. Thus, no optical chopper is needed. Also, no bias supply, another potential source of 1/f noise, is needed. Cooled quantum detectors were not practical, considering the duration and weight constraints of the Viking Mission. The array was made by evaporating the various components onto a sapphire film using photoetched masks for dimensional control. The film, about 200 nm thick, is supported by a sapphire disk. The film was made by anodizing aluminum foil and etching away the aluminum. The black circular dots in the figure are the sensitive areas overlaid with bismuth mass. Characteristics Active area 7.E-4 cm**2 Number of junctions 6 Resistance 13.E3 ohm Time constant 80-100 msec Responsivity 130 V/Watt Detectivity (D*) 2.E8 cm_Hz**0.5_W**-1 To obtain full sensitivity the detectors must be evacuated. Therefore, during ground testing the detector packages were pumped down through a permanently attached manifold. At other times the detector packages were backfilled with xenon to protect the detectors while still allowing gross sensitivity checks. To avoid exposure to moisture during the long period prior to launch when the IRTM was mounted on the spacecraft and could not be sealed, the manifold was kept at a slight positive pressure by a continuous flow of high purity nitrogen. The manifold was opened to space by launch vehicle separation. Sensitivity ----------- The detectivity is 2.E8 CM_HZ**0.5_W**-1 Instrument Electronics 'IRTM' ============================= Description ----------- The signal channels use a synchronous demodulation scheme to provide good stability and to avoid 1/f noise in the preamp. The input FET chopper is a full-wave type operating at 471 Hz. This and the center-tapped thermopile allow voltage doubling of the detector signal and noise and thus reduce the preamp noise contribution which otherwise would be significant. The differential input connection, while suffering a square root (2) noise disadvantage compared to single-ended input, provides excellent common mode rejection of chopper spikes and other input noise. Temperature dependence of the thermopile, about -0.5%/degree C., is compensated by a thermister network external to the hybrid package. Preamp gain is adjustable with an external resistor. Following the half-wave synchronous demodulator is an integrate, hold, and reset circuit with an integrate time of 981 msec. The integrator serves as a low pass filter while the hold feature ensures spatial simultaneity of corresponding detectors in each telescope. After completion of sampling by the multiplexer, all channel hold circuits are reset to ensure independence of data samples. The IRTM analog signals, which have a range of +/- 6V, are digitized by the analog-to-pulse width converter and flight data subsystem (FDS) counter into +/- 2**9 levels, yielding 1023 data numbers (DN) which are nearly linear with radiance in each channel. The IRTM multiplexer consists of sixty-eight FET switches and a buffer signal amplifier. In addition to thirty-two data channels (twenty-eight active and four spare), thirty-two channels of engineering data are also sample. These include eight temperature measurements from thermisters located at four locations on the reference plate, the electronics module, and each of the three ir detector packages (telescopes A, B, C). Three power supply voltages and the pre-dc restore voltage of twenty-one channels (telescopes A, B, and C) are monitored. The pre-dc restore monitors are diagnostic to determine the presence of large thermal or detector offsets. The scan mirror is driven by a four-position stepper motor through a 50/1 gear reduction. A motor drive pulse duration of 40 msec allows a 90 degree mirror rotation in 2 sec. The mirror position is sensed by a two-bit encoder on the motor shaft; the contacts at the three desired positions are about half of the width of 1.8 degree mirror step. The motor stepping is controlled by the FDS using a comparison of the encoder readout with the desired position originating either from the FDS normal mode clock or direct ground command; the motor cannot be directly commanded. In addition to the restore which occurs automatically in the normal model when the mirror reaches the space position, restores can be ground commanded when the IRTM is in the fixed planet or fixed space mode; in either case housekeeping data are multiplexed into the data stream during the 1-sec restore period. Whenever the mirror reaches the reference position, the calibration lamp is turned on for the next two integration periods. The lamp is at full radiance throughout the second integration period, which is used for gain determination of the D telescope channels. In the fixed reference mode, science and housekeeping data are sampled alternatively. Instrument Filter 'A - T20' =========================== Filter Name : T20 Filter Type : RESTSTRAHLEN Minimum Wavelength : 17.700000 Maximum Wavelength : 30.000000 Center Filter Wavelength : 21.000000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'B - T11' =========================== Filter Name : T11 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 9.800000 Maximum Wavelength : 12.500000 Center Filter Wavelength : 11.200000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'C1 - T7' =========================== Filter Name : T7 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 6.100000 Maximum Wavelength : 8.300000 Center Filter Wavelength : 7.200000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'C2 - T9' =========================== Filter Name : T9 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 8.300000 Maximum Wavelength : 9.800000 Center Filter Wavelength : 9.000000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'C3 - T15' ============================ Filter Name : T15 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 14.560000 Maximum Wavelength : 15.410000 Center Filter Wavelength : 15.000000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'D - SOLAR UV-22' =================================== Filter Name : SOLAR UV-22 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 0.300000 Maximum Wavelength : 3.000000 Center Filter Wavelength : 1.600000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the planet port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Optics 'A' ===================== Telescope Diameter : 0.058000 Telescope F Number : 3.500000 Telescope Focal Length : 0.203000 Telescope Resolution : 0.005100 Telescope T Number : UNK Telescope Transmittance : UNK Description ----------- The A telescope (17.7-24 micrometer) is shown schematically in Fig. 3 of CHASE_ETAL_1978. It is an f/3.5, 20.3-cm focal length Cassegrainian design with an aperture diameter of 5.8-cm., spherical surfaces, and, except for mirror materials, is identical to the B and C telescopes. By using relatively slow fore optics, degradation of filter sharpness normally caused by operating an interference filter in a low f-number beam is negligible. The focal plane contains a field-defining aperture plate with seven 0.107-cm diameter holes arranged in a chevron pattern. The fields of view thus defined are nested with those of the MAWD and imaging systems (Fig. 4 of CHASE_ETAL_1978). Behind each hole in the field stop plate is a lens which produces a 0.0254-cm diam image of the telescope aperture on the detector, which itself is about the same size. The final optical speed at the detector is f/1. Optical materials used in the four telescopes are shown in Table II, and the resulting spectral response is shown in Fig. 5 of CHASE_ETAL_1978. Mirrors are made of hot-pressed uncoated zinc oxide for both primary and secondary mirrors. The reststrahlen reflection properties of ZnO are the major factors in the A telescope spectral response. Minimizing extrafield sensitivity (EFS) was an important aspect of the optical design since on previous Mariner radiometers EFS contribution seriously compromised observations of scenes near large temperature contrasts (points near the planetary limb and polar caps). During instrumentation development, IRTM image quality was determined in two angular regions. In the near-field region, a laboratory collimator and ir source were used to measure the 2-D spatial response out to 16-mrad diam (three fields of view). Point source field of view measurements in this region are shown in Fig. 6 of CHASE_ETAL_1978. For far field measurements, sensitivity constraints dictated an approach in which the fraction of energy within a given angular annulus is measured. A 30.5-cm diam, concentric grooved, blackbody plate with a series of restricting apertures was used at several distances (30.5-cm, 140-cm, and 610-cm) to define angular response regions from about one field of view out to 1-rad diam. That is, with the telescope focused at 610-cm, a disk 3.17-cm in diameter at that distance defines one half-response field of view (5.2 mrad). The source was held at 95 degrees C. by a heater/regulator and integral water jacket. To prevent difficulties with atmospheric transmission, the entire apparatus was contained in a polyethylene bag flushed with dry N2. The EFS problem was more severe for the longer wavelength A telescope than the others, possibly owing to the higher reflectance at longer wavelengths of the black paint used inside the telescope. Tests using this apparatus led to several telescope modifications designed to reduce EFS (see Fig. 3 of CHASE_ETAL_1978): (1) A postfocal baffle was placed between the field lens and the detectors to confine energy to the sensitive area of the detectors. (2) A spider baffle, added to the outer edges of the secondary mirror support spider, was designed to reduce reflection off the sides of the spider legs. (3) A cone baffle coated with CTL 15 black paint was placed on the central dead spot of the secondary mirror. This was designed to prevent focal plane reflections from falling on the detectors. Of these three modifications, only the cone baffle gave significant improvement, although all three were incorporated in the design. These results of the final EFS measurements are shown in Fig. 6 of CHASE_ETAL_1978. The calculated response due to diffraction and the measured values are shown. The integrated EFS response between 12 mrad and 1-rad diam was about 4%. Of this, about 1/2 is due to diffraction effects. The effect of response outside of the nominal field of view can be estimated directly from data obtained on scans across the hot (subsolar) planetary limb. Assuming that the response is circularly symmetric, and all evidence indicates this to be closely followed, the signature of a half space would also be symmetric. A plot of fractional energy derived from a Viking 1 IRTM scan across the sunlit limb of Mars is shown in Fig. 6 of CHASE_ETAL_1978. The alignment was determined using a 20.3-cm (8-in.) collimator to illuminate all four telescopes with a small source of high temperature blackbody radiation. Measurements were taken simultaneously in twenty-eight channels over a 1.5-mrad square grid pattern. For each channel, a parabolic ellipsoid was fit to data where the measured intensity was more than 10% of the peak intensity in that channel. The alignment of each telescope was ascertained by combining the center of response so determined for the seven channels in the telescope. This procedure allowed for the alignment of the four telescopes to be determined with an estimated precision of 0.1 mrad. The back of the secondary mirror of the B telescope was aluminized and used as the alignment reference for this procedure and for instrument alignment on the spacecraft. The instrument pointing direction was verified in the same manner just prior to planetary encounter using Mars as a 5-mrad diam source and using the science platform motion to generate a 5-mrad spaced grid. The in-flight alignment is shown in Fig. 4 of CHASE_ETAL_1978. Instrument Optics 'B' ===================== Telescope Diameter : 0.058000 Telescope F Number : 3.500000 Telescope Focal Length : 0.203000 Telescope Resolution : 0.005100 Telescope T Number : UNK Telescope Transmittance : UNK Description ----------- The A telescope (17.7-24 micrometer) is shown schematically in Fig. 3 of CHASE_ETAL_1978. It is an f/3.5, 20.3-cm focal length Cassegrainian design with an aperture diameter of 5.8-cm., spherical surfaces, and, except for mirror materials, is identical to the B and C telescopes. By using relatively slow fore optics, degradation of filter sharpness normally caused by operating an interference filter in a low f-number beam is negligible. The focal plane contains a field-defining aperture plate with seven 0.107-cm diameter holes arranged in a chevron pattern. The fields of view thus defined are nested with those of the MAWD and imaging systems (Fig. 4 of CHASE_ETAL_1978). Behind each hole in the field stop plate is a lens which produces a 0.0254-cm diam image of the telescope aperture on the detector, which itself is about the same size. The final optical speed at the detector is f/1. Optical materials used in the four telescopes are shown in Table II, and the resulting spectral response is shown in Fig. 5 of CHASE_ETAL_1978. The B mirror is made of aluminized and SiO overcoated fused silica. The spectral bandpass of the ir channel is determined by interference bandpass filter and an AR coated detector lense. The out-of-band response for the B telescope is less than 0.1% of full scale for an object of 1.E-6 the radiance of a 5800-K blackbody, the level expected for reflectance from the subsolar region of Mars. Minimizing extrafield sensitivity (EFS) was an important aspect of the optical design since on previous Mariner radiometers EFS contribution seriously compromised observations of scenes near large temperature contrasts (points near the planetary limb and polar caps). During instrumentation development, IRTM image quality was determined in two angular regions. In the near-field region, a laboratory collimator and ir source were used to measure the 2-D spatial response out to 16-mrad diam (three fields of view). Point source field of view measurements in this region are shown in Fig. 6 of CHASE_ETAL_1978. For far field measurements, sensitivity constraints dictated an approach in which the fraction of energy within a given angular annulus is measured. A 30.5-cm diam, concentric grooved, blackbody plate with a series of restricting apertures was used at several distances (30.5-cm, 140-cm, and 610-cm) to define angular response regions from about one field of view out to 1-rad diam. That is, with the telescope focused at 610-cm, a disk 3.17-cm in diameter at that distance defines one half-response field of view (5.2 mrad). The source was held at 95 degrees C. by a heater/regulator and integral water jacket. To prevent difficulties with atmospheric transmission, the entire apparatus was contained in a polyethylene bag flushed with dry N2. Tests using this apparatus led to several telescope modifications designed to reduce EFS (see Fig. 3 of CHASE_ETAL_1978): (1) A postfocal baffle was placed between the field lens and the detectors to confine energy to the sensitive area of the detectors. (2) A spider baffle, added to the outer edges of the secondary mirror support spider, was designed to reduce reflection off the sides of the spider legs. (3) A cone baffle coated with CTL 15 black paint was placed on the central dead spot of the secondary mirror. This was designed to prevent focal plane reflections from falling on the detectors. Of these three modifications, only the cone baffle gave significant improvement, although all three were incorporated in the design. These results of the final EFS measurements are shown in Fig. 6 of CHASE_ETAL_1978. The calculated response due to diffraction and the measured values are shown. The integrated EFS response between 12 mrad and 1-rad diam was about 4%. Of this, about 1/2 is due to diffraction effects. The effect of response outside of the nominal field of view can be estimated directly from data obtained on scans across the hot (subsolar) planetary limb. Assuming that the response is circularly symmetric, and all evidence indicates this to be closely followed, the signature of a half space would also be symmetric. A plot of fractional energy derived from a Viking 1 IRTM scan across the sunlit limb of Mars is shown in Fig. 6 of CHASE_ETAL_1978. The alignment was determined using a 20.3-cm (8-in.) collimator to illuminate all four telescopes with a small source of high temperature blackbody radiation. Measurements were taken simultaneously in twenty-eight channels over a 1.5-mrad square grid pattern. For each channel, a parabolic ellipsoid was fit to data where the measured intensity was more than 10% of the peak intensity in that channel. The alignment of each telescope was ascertained by combining the center of response so determined for the seven channels in the telescope. This procedure allowed by the alignment of the four telescopes to be determined with an estimated precision of 0.1 mrad. The back of the secondary mirror of the B telescope was aluminized and used as the alignment reference for this procedure and for instrument alignment on the spacecraft. The instrument pointing direction was verified in the same manner just prior to planetary encounter using Mars as a 5-mrad diam source and using the science platform motion to generate a 5-mrad spaced grid. The in-flight alignment is shown in Fig. 4 of CHASE_ETAL_1978. Instrument Optics 'C' ===================== Telescope Diameter : 0.058000 Telescope F Number : 3.500000 Telescope Focal Length : 0.203000 Telescope Resolution : 0.005100 Telescope T Number : UNK Telescope Transmittance : UNK Description ----------- The A telescope (17.7-24 micrometer) is shown schematically in Fig. 3 of CHASE_ETAL_1978. It is an f/3.5, 20.3-cm focal length Cassegrainian design with an aperture diameter of 5.8-cm., spherical surfaces, and, except for mirror materials, is identical to the B and C telescopes. The focal plane contains a field-defining aperture plate with seven 0.107-cm diameter holes arranged in a chevron pattern. The fields of view thus defined are nested with those of the MAWD and imaging systems (Fig. 4 of CHASE_ETAL_1978). Behind each hole in the field stop plate is a lens which produces a 0.0254-cm diam image of the telescope aperture on the detector, which itself is about the same size. The final optical speed at the detector is f/1. Optical materials used in the four telescopes are shown in Table II, and the resulting spectral response is shown in Fig. 5 of CHASE_ETAL_1978. Mirrors are made of aluminized and SiO overcoated fused silica except for the A telescope, which uses hot-pressed uncoated zinc oxide for both primary and secondary mirrors. The spectral bandpass of the other ir channels is determined by interference bandpass filters and AR coated detector lenses. The out-of-band response for the B and C telescopes is less than 0.1% of full scale for an object of 1.E-6 the radiance of a 5800-K blackbody, the level expected for reflectance from the subsolar region of Mars. The A band has less than 0.1% response for wavelengths less than 16 micrometer, and wavelengths longer than 30 micrometer are limited by the Irtran 6 field lens. Minimizing extrafield sensitivity (EFS) was an important aspect of the optical design since on previous Mariner radiometers EFS contribution seriously compromised observations of scenes near large temperature contrasts (points near the planetary limb and polar caps). During instrumentation development, IRTM image quality was determined in two angular regions. In the near-field region, a laboratory collimator and ir source were used to measure the 2-D spatial response out to 16-mrad diam (three fields of view). Point source field of view measurements in this region are shown in Fig. 6 of CHASE_ETAL_1978. For far field measurements, sensitivity constraints dictated an approach in which the fraction of energy within a given angular annulus is measured. A 30.5-cm diam, concentric grooved, blackbody plate with a series of restricting apertures was used at several distances (30.5-cm, 140-cm, and 610-cm) to define angular response regions from about one field of view out to 1-rad diam. That is, with the telescope focused at 610-cm, a disk 3.17-cm in diameter at that distance defines one half-response field of view (5.2 mrad). The source was held at 95 degrees C. by a heater/regulator and integral water jacket. To prevent difficulties with atmospheric transmission, the entire apparatus was contained in a polyethylene bag flushed with dry N2. Tests using this apparatus led to several telescope modifications designed to reduce EFS (see Fig. 3 of CHASE_ETAL_1978): (1) A postfocal baffle was placed between the field lens and the detectors to confine energy to the sensitive area of the detectors. (2) A spider baffle, added to the outer edges of the secondary mirror support spider, was designed to reduce reflection off the sides of the spider legs. (3) A cone baffle coated with CTL 15 black paint was placed on the central dead spot of the secondary mirror. This was designed to prevent focal plane reflections from falling on the detectors. Of these three modifications, only the cone baffle gave significant improvement, although all three were incorporated in the design. These results of the final EFS measurements are shown in Fig. 6 of CHASE_ETAL_1978. The calculated response due to diffraction and the measured values are shown. The integrated EFS response between 12 mrad and 1-rad diam was about 4%. Of this, about 1/2 is due to diffraction effects. The effect of response outside of the nominal field of view can be estimated directly from data obtained on scans across the hot (subsolar) planetary limb. Assuming that the response is circularly symmetric, and all evidence indicates this to be closely followed, the signature of a half space would also be symmetric. A plot of fractional energy derived from a Viking 1 IRTM scan across the sunlit limb of Mars is shown in Fig. 6 of CHASE_ETAL_1978. The alignment was determined using a 20.3-cm (8-in.) collimator to illuminate all four telescopes with a small source of high temperature blackbody radiation. Measurements were taken simultaneously in twenty-eight channels over a 1.5-mrad square grid pattern. For each channel, a parabolic ellipsoid was fit to data where the measured intensity was more than 10% of the peak intensity in that channel. The alignment of each telescope was ascertained by combining the center of response so determined for the seven channels in the telescope. This procedure allowed by the alignment of the four telescopes to be determined with an estimated precision of 0.1 mrad. The back of the secondary mirror of the B telescope was aluminized and used as the alignment reference for this procedure and for instrument alignment on the spacecraft. The instrument pointing direction was verified in the same manner just prior to planetary encounter using Mars as a 5-mrad diam source and using the science platform motion to generate a 5-mrad spaced grid. The in-flight alignment is shown in Fig. 4 of CHASE_ETAL_1978. Instrument Optics 'D' ===================== Telescope Diameter : 0.037000 Telescope F Number : 5.500000 Telescope Focal Length : 0.203000 Telescope Resolution : UNK Telescope T Number : UNK Telescope Transmittance : UNK Description ----------- The D telescope has a reduced aperture of 3.7 cm and a focal length of f/5.5. By using relatively slow fore optics, degradation of filter sharpness normally caused by operating an interference filter in a low f-number beam is negligible. The focal plane contains a field-defining aperture plate with seven 0.107-cm diam holes arranged in a chevron pattern. The fields of view thus defined are nested with those of the MAWD and imaging systems (Fig. 4 of CHASE_ETAL_1978). Behind each hole in the field stop plate is a lens which produces a 0.0254-cm diam image of the telescope aperture on the detector, which itself is about the same size. The final optical speed at the detector is f/1. Optical materials used in the four telescopes are shown in Table II, and the resulting spectral response is shown in Fig. 5 of CHASE_ETAL_1978. Mirrors are made of aluminized and SiO overcoated fused silica except for the A telescope, which uses hot-pressed uncoated zinc oxide for both primary and secondary mirrors. The spectral bandpass of the other ir channels is determined by interference bandpass filters and AR coated detector lenses. The transmission elements of the D telescope insure that it is thermally blind. Special coatings on the D telescope mirrors were used to obtain a reasonably gray response to solar radiation. Minimizing extrafield sensitivity (EFS) was an important aspect of the optical design since on previous Mariner radiometers EFS contribution seriously compromised observations of scenes near large temperature contrasts (points near the planetary limb and polar caps). During instrumentation development, IRTM image quality was determined in two angular regions. In the near-field region, a laboratory collimator and ir source were used to measure the 2-D spatial response out to 16-mrad diam (three fields of view). Point source field of view measurements in this region are shown in Fig. 6 of CHASE_ETAL_1978. For far field measurements, sensitivity constraints dictated an approach in which the fraction of energy within a given angular annulus is measured. A 30.5-cm diam, concentric grooved, blackbody plate with a series of restricting apertures was used at several distances (30.5-cm, 140-cm, and 610-cm) to define angular response regions from about one field of view out to 1-rad diam. That is, with the telescope focused at 610-cm, a disk 3.17-cm in diameter at that distance defines one half-response field of view (5.2 mrad). The source was held at 95 degrees C. by a heater/regulator and integral water jacket. To prevent difficulties with atmospheric transmission, the entire apparatus was contained in a polyethylene bag flushed with dry N2. The EFS problem was more severe for the longer wavelength A telescope than the others, possibly owing to the higher reflectance at longer wavelengths of the black paint used inside the telescope. Tests using this apparatus led to several telescope modifications designed to reduce EFS (see Fig. 3 of CHASE_ETAL_1978): (1) A postfocal baffle was placed between the field lens and the detectors to confine energy to the sensitive area of the detectors. (2) A spider baffle, added to the outer edges of the secondary mirror support spider, was designed to reduce reflection off the sides of the spider legs. (3) A cone baffle coated with CTL 15 black paint was placed on the central dead spot of the secondary mirror. This was designed to prevent focal plane reflections from falling on the detectors. Of these three modifications, only the cone baffle gave significant improvement, although all three were incorporated in the design. These results of the final EFS measurements are shown in Fig. 6 of CHASE_ETAL_1978. The calculated response due to diffraction and the measured values are shown. The integrated EFS response between 12 mrad and 1-rad diam was about 4%. Of this, about 1/2 is due to diffraction effects. The effect of response outside of the nominal field of view can be estimated directly from data obtained on scans across the hot (subsolar) planetary limb. Assuming that the response is circularly symmetric, and all evidence indicates this to be closely followed, the signature of a half space would also be symmetric. A plot of fractional energy derived from a Viking 1 IRTM scan across the sunlit limb of Mars is shown in Fig. 6 of CHASE_ETAL_1978. The alignment was determined using a 20.3-cm (8-in.) collimator to illuminate all four telescopes with a small source of high temperature blackbody radiation. Measurements were taken simultaneously in twenty-eight channels over a 1.5-mrad square grid pattern. For each channel, a parabolic ellipsoid was fit to data where the measured intensity was more than 10% of the peak intensity in that channel. The alignment of each telescope was ascertained by combining the center of response so determined for the seven channels in the telescope. This procedure allowed by the alignment of the four telescopes to be determined with an estimated precision of 0.1 mrad. The instrument pointing direction was verified in the same manner just prior to planetary encounter using Mars as a 5-mrad diam source and using the science platform motion to generate a 5-mrad spaced grid. The in-flight alignment is shown in Fig. 4 of CHASE_ETAL_1978. Instrument Mode 'FIXED PLANET' ============================== Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperatureand a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. In the FIXED PLANET mode, the first 0,2, or 4 ICKs could be housekeeping data while the mirror was in motion to the planet position. Thereafter the instrument reported planet data untill the next command was received. Instrument Mode 'FIXED REFERENCE' ================================= Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperatureand a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. In the FIXED REFERENCE mode, the mirror was commanded to the reference position; 0 to 5 ICKS of housekeeping data were possible while the mirror was in motion. Thereafter, the instrument reported radiance readings or housekeeping data on alternate ICKs untill the next command was received. Instrument Mode 'FIXED SPACE' ============================= Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperatureand a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. In the FIXED SPACE mode, the mirror was commanded to the space position from wherever it had been, with 2 ICKs of housekeeping data if the mirror was not already in the space position. Thereafter the instrument reported space data until another command was received. Instrument Mode 'MODIFIED NORMAL' ================================= Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperatureand a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. A MODIFIED normal mode was also available, in which the only space view was the first of the cycle, followed by 243 ICKs of planet data. In NORMAL mode, ICKs 1 and 2 were housekeeping data while the mirror moved to space. ICK 3 was the space level before reset. During ICK 4, the electronics for all channels were reset so that the sensed radiance (meant to be the cosmic background level of essentially zero radiance) yielded a data number (DN) of a few. There was a filter on the reset so that the voltage change was only about 2/3 of the way to the space radiance level; this smoothed out the zero setting, but also meant that several cycles were required to recover from a serious drift. ICK 5 was still in the space position and yielded the DN response to space. Ick 6 and 7 were housekeeping data while the mirror moved to the reference position. ICK 8 and 9 were the DN response to the reference surface; only the second reading was used in calibration of the solar channel to allow the lamp filament to warm up completely. ICKs 10 through 13 were housekeeping data while the mirror moved to the planet position. The 57 ICKs 14-64 were planet data. The 7 ICK cycle to space, with reset of the zero-radiance DN level in all channels, was repeated each 64 ICKs, beginning on ICKs 65, 129, and 193, with motion directly back to the planet position for another 57 ICKs of planet data. Instrument Mode 'NORMAL' ======================== Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperature and a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. The NORMAL mode sequenced the pointing to PLANET most of the time, with pointing to SPACE at intervals of 64 ICKs, and to REFERENCE at intervals of 256 ICKs. ICK is a one syllable acronym for 'incremental counter keeper' and represents 1.12 second duration, the basic time interval of IRTM operation. It required 2 ICKs for the mirror to move 90 degrees and settle; whenever the mirror was in motion the downlink data contained housekeeping information about instrument status and detector voltage levels. In NORMAL mode, ICKs 1 and 2 were housekeeping data while the mirror moved to space. ICK 3 was the space level before reset. During ICK 4, the electronics for all channels were reset so that the sensed radiance (meant to be the cosmic background level of essentially zero radiance) yielded a data number (DN) of a few. There was a filter on the reset so that the voltage change was only about 2/3 of the way to the space radiance level; this smoothed out the zero setting, but also meant that several cycles were required to recover from a serious drift. ICK 5 was still in the space position and yielded the DN response to space. Ick 6 and 7 were housekeeping data while the mirror moved to the reference position. ICK 8 and 9 were the DN response to the reference surface; only the second reading was used in calibration of the solar channel to allow the lamp filament to warm up completely. ICKs 10 through 13 were housekeeping data while the mirror moved to the planet position. The 57 ICKs 14-64 were planet data. The 7 ICK cycle to space, with reset of the zero-radiance DN level in all channels, was repeated each 64 ICKs, beginning on ICKs 65, 129, and 193, with motion directly back to the planet position for another 57 ICKs of planet data. Mounted On Platform 'SCAN PLATFORM' =================================== Cone Offset Angle : 0.070000 Cross Cone Offset Angle : 0.030000 Description ----------- OFFSET ANGLE SCALED FROM FIGURE 4 OF CHASE_ETAL_1978; these were determined by scans across Mars during approach, when the angular diameter of the planet was 1.93 and 4.79 milliradians (VO-1)
• instrument : INFRARED THERMAL MAPPER for VO2
  INSTRUMENT: INFRARED THERMAL MAPPER SPACECRAFT: VIKING ORBITER 2 Instrument Information ====================== Instrument Id : IRTM Instrument Host Id : VO2 Pi Pds User Id : HKIEFFER Instrument Name : UNK Instrument Type : RADIOMETER Build Date : 1974 Instrument Mass : 8.400000 Instrument Length : 0.330000 Instrument Width : 0.267000 Instrument Height : 0.178000 Instrument Serial Number : 005 Instrument Manufacturer Name : SANTA BARBARA RESEARCH CENTER Instrument Description ====================== The IRTM contains four small Cassegrainian telescopes which each image the same, seven circular areas. There is a total of twenty-eight channels in four surface and one atmospheric thermal band from 6 micrometer to 30 micrometer and a broad solar reflectance band. All channels are sampled simultaneously, using the spacecraft scanning capability to map the radiance over small and large areas of the planet. All channels use thermopile detectors; spectral passbands are determined by a combination of interference filters, detector lens materials, antireflection coatings, and reststrahlen optics. The scan modes are described in the PDS INSTRUMENT MODE DESCRIPTION. Science Objectives ================== The objective of the Viking Orbiter infrared thermal mapper (IRTM) is to measure the thermal emission of the Martian surface and atmosphere and total reflected sunlight with high spatial and flux resolution. Operational Considerations ========================== Most low and moderate resolution IRTM data were acquired through using 'box scans'. These were commonly acquired between 1-6 hours from periapsis, and utilized the scan platform to slew back and forth in cone angle (in the direction the IRTM chevron points) with small offsets in the same direction between these oscillating slews. Ignoring spacecraft motion, this pattern would generate bi-directional evenly spaced scans with the seven IRTM detectors. Spacecraft motion during the scan sequence, typically of 10-40 minutes duration, created some distortion in this otherwise uniform pattern. Typical resulting scans across the planetary surface are shown in Figure 3 of Kieffer et al., 1976. These scans were usually designed to extend slightly off the limb of the planet on at least one side. These 'planet port' off-planet data provided the best estimates of the zero radiance response of the instrument. When the spacecraft was near periapsis, the apparent motion of the planetary surface relative to the spacecraft was too rapid to allow oscillating slews. At these times, the instrument would simply 'stare' in one direction and use the spacecraft motion to sweep the detector pattern across the surface. These observations were usually acquired in Normal Mode, but occasionally Fixed Planet was used. At irregular times through the mission, 'phase function' observations were made. These involved using the two axis scan platform to follow one point on the ground as the spacecraft went from horizon to horizon relative to this surface point. In actuality, this sequence was acquired using a small number of discrete scan platform moves, allowing the instrument to 'stare' across a short stripe centered on the target point between slews. Such 'phase function' observations typically yielded about 10 different viewing geometries within a single sequence. These observations were particularly useful in determining the influence of the atmosphere. In preparation of the IRTM data set, all observations which were more than 1 1/2 degrees apparent angle above the nearest limb of the planet were deleted. Geometry Errors Due to Uncertain Timing: Early and late during the Viking mission, orbital solutions based on the tracking telemetry were determined every few days. During VO-1 revolution 175-603 and VO-2 revolutions 118-521, orbital solutions were often separated by a week or more. Because there is significant irregularity in the Martian gravitional field, these irregularities could slowly influence the orbit of the Viking spacecraft in unpredictable ways. The primary influence was in the period of the orbit, resulting in uncertainty as to exactly where the spacecraft was along its orbit at any specific time. These uncertainties were as large as 75 seconds in the worst case. Far from periapsis, these timing uncertainties were not of major significance because the spacecraft velocities were low and the projected fields of views on the planet were large. However, near periapsis, the IRTM field of view could move across the surface equivalent to its full width in as little as one second. Thus, when there was a large timing error, the computed ground intercept locations could be in error by many fields of view. In the worst case, these positions may be in error by up to 200 km. When the magnitude of this problem was discovered, the SEDR (geometry calculations) for the imaging instrument was rerun with revised orbit solutions. However, it was impractical to regenerate the IRTM SEDR and these errors have not been corrected. There was an attempt by the navigational team to estimate the magnitude of the timing error for both Viking spacecraft for those revolutions through the affected part of the Viking mission. This is described in the 1980 April 14 memo by Frank Palluconi, which contains estimates of the magnitude of the error for each revolution. Hugh Kieffer has a copy (the sole surviving copy?) of this memo. A direct determination of the timing offset can be made from the IRTM data alone in those instances when thermal patterns can be unambiguously identified with surface features. Since the dominant geometric error is in time, maps of thermal patterns (typically as contours of observed temperature minus the calculated standard model temperature) can be slid across the cartographic map parallel to the subspacecraft track (if the instrument was in fixed planet mode, this is simply sliding the IRTM trace along its own path) until the thermal and cartographic features are aligned. Because there are small gaps in the IRTM coverage every 64 ICKs, the amount the IRTM pattern must be shifted to agree with the surface morphology can be scaled directly into a timing offset in seconds. This has been done for a variety of high resolution scans across Arsia Mons (by Jim Zimbelman) and for many scans across Valles Marineris (by David Paige and Hugh Kieffer). A set of known offsets is slowly accumulating. Hugh Kieffer has a copy (the sole surviving copy?) of the memo discussing this problem. Calibration Description ======================= Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the planet port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Telescope D channels were calibrated using a different method. The radiance source was a mercury-xenon lamp and narrowband filter centered at 0.896 micrometer with a bandwidth of 425 nm. The in-band radiance of the lamp was known by direct comparison with a standard lamp acquired from the National Bureau of Standards, using a silicon photodiode as a transfer standard. The relative spectral response measurements then allowed extension of the one-point absolute calibration to the entire passband. Gains for the D channels were set to give full scale for 75% of the diffuse reflection of solar irradiance at Mars average distance from the sun. Using integrals of the Planck function and the measured spectral response, the flux response of the IRTM is found to be close to linear in the thermal channels. The best fit quadratic functions, normalized to full scale, typically had constant and quadratic coefficients of 0.002 and 0.02, respectively. The solar band channels, which had much higher absolute flux levels at full scale, showed a decrease in response at high signal levels corresponding to a quadratic coefficient of 0.07. With the IRTM in the vacuum chamber, the instrument response was measured at four lamp currents. An additional series of wide band measurements utilizing a NBS standard lamp and a barium sulfate diffusing screen, in which only the lamp-screen distance was changed, was used to determine in detail the solar band nonlinearity. During spacecraft thermal-vacuum testing and in flight, a small drift of about 1-min duration was found to be induced when the scan mirror moved to the reference position in normal mode. This appears to be caused by the decrease in radiative heat loss from the instrument when the telescopes do not view space. The shape of this postreference drift was accurately determined during normal mode sequences when the spacecraft was well away from Mars, and this effect is removed in the data reduction. The change of the thermal state of the IRTM caused by large scan platform slew or planetary radiation near periapsis can introduce significant drifts of the zero-flux level. These shifts have a time constant of 1-2 min or longer, and their magnitude increases with inband wavelength and preamplifier gain. It is probably due primarily to very small temperature gradients induced in the detector packages as the general instrument temperature changes. A significant design feature of the IRTM is that the space DN level of each channel is measured immediately prior to and after the restore which occurs each minute in normal mode. A linear interpolation between these zero-flux DN levels is used in data decalibration. The remaining quadratic and higher order drift is generally negligible. Section 'IRTM' ============== Total Fovs : 7 Data Rate : 250.000000 Sample Bits : 10 'IRTM' Detectors ---------------- A 'IRTM' Electronics ------------------ IRTM 'IRTM' Filters -------------- SOLAR UV-22 T11 T15 T20 T7 T9 'IRTM' Section Optic IDs ------------------------ A B C D In modes -------- FIXED PLANET FIXED REFERENCE FIXED SPACE MODIFIED NORMAL NORMAL 'IRTM' Section FOV Shape 'CIRCULAR' ----------------------------------- Section Id : IRTM Fovs : 7 Horizontal Pixel Fov : 0.292000 Vertical Pixel Fov : 0.292000 Horizontal Fov : 2.402000 Vertical Fov : 1.347000 'IRTM' Section Parameter 'RADIANCE A' ------------------------------------- The A telescope measured wavelengths between 16 and 30 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE A Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.002030 Noise Level : 0.000001 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE B' ------------------------------------- The B telescope measured wavelengths between 10 and 13 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE B Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.003120 Noise Level : 0.000001 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE C1' -------------------------------------- The C1 set of 3 detectors (out of 7 in the C telescope) were limited by filtering to wavelengths between 6 and 8 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE C1 Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.003190 Noise Level : 0.000001 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE C2' -------------------------------------- The C2 set of 3 detectors (out of 7 in the C telescope) were limited by filtering to wavelengths between 8 and 10 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE C2 Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.001980 Noise Level : 0.000001 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE C3' -------------------------------------- The C3 detector/filter combination within the C telescope responded to wavelengths between 14.5 and 15.5 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE C3 Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.006340 Noise Level : 0.000003 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND 'IRTM' Section Parameter 'RADIANCE D' ------------------------------------- The D telescope measured wavelengths between 0.3 and 3.0 microns. This parameter is the radiance in that band. Instrument Parameter Name : RADIANCE D Sampling Parameter Name : TIME Instrument Parameter Unit : WATT_METER**-2_MICROMETER**-1 Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 135.840000 Noise Level : 0.030000 Sampling Parameter Interval : 1.120000 Sampling Parameter Resolution : 1.120000 Sampling Parameter Unit : SECOND Instrument Detector 'A' ======================= Detector Type : THERMOPILE ARRAY Detector Aspect Ratio : 1.000000 Minimum Wavelength : 0.300000 Maximum Wavelength : 100.000000 Nominal Operating Temperature : 275.000000 Description ----------- The seven-element thin-film antimony-bismuth thermopile array used in the IRTM is shown in Fig. 7 of CHASE_ETAL_1978. The chevron arrangement was based on the need for uniform coverage irrespective of scan platform orientation; it also allowed the detectors to all be approximately the same distance from the telescope optic axis. In this application thermopiles were found to be better than other thermal detectors because they operate to dc and exhibit no 1/f noise. Thus, no optical chopper is needed. Also, no bias supply, another potential source of 1/f noise, is needed. Cooled quantum detectors were not practical, considering the duration and weight constraints of the Viking Mission. The array was made by evaporating the various components onto a sapphire film using photoetched masks for dimensional control. The film, about 200 nm thick, is supported by a sapphire disk. The film was made by anodizing aluminum foil and etching away the aluminum. The black circular dots in the figure are the sensitive areas overlaid with bismuth oxide smoke which has good ir absorptivity but low thermal mass. Characteristics Active area 7.E-4 cm**2 Number of junctions 6 Resistance 13.E3 ohm Time constant 80-100 msec Responsivity 130 V/Watt Detectivity (D*) 2.E8 cm_Hz**0.5_W**-1 To obtain full sensitivity the detectors must be evacuated. Therefore, during ground testing the detector packages were pumped down through a permanently attached manifold. At other times the detector packages were backfilled with xenon to protect the detectors while still allowing gross sensitivity checks. To avoid exposure to moisture during the long period prior to launch when the IRTM was mounted on the spacecraft and could not be sealed, the manifold was kept at a slight positive pressure by a continuous flow of high purity nitrogen. The manifold was opened to space by launch vehicle separation. Sensitivity ----------- The detectivity is 2.E8 CM_HZ**0.5_W**-1 Instrument Electronics 'IRTM' ============================= Description ----------- The signal channels use a synchronous demodulation scheme to provide good stability and to avoid 1/f noise in the preamp. The input FET chopper is a full-wave type operating at 471 Hz. This and the center-tapped thermopile allow voltage doubling of the detector signal and noise and thus reduce the preamp noise contribution which otherwise would be significant. The differential input connection, while suffering a square root (2) noise disadvantage compared to single-ended input, provides excellent common mode rejection of chopper spikes and other input noise. Temperature dependence of the thermopile, about -0.5%/degree C., is compensated by a thermister network external to the hybrid package. Preamp gain is adjustable with an external resistor. Following the half-wave synchronous demodulator is an integrate, hold, and reset circuit with an integrate time of 981 msec. The integrator serves as a low pass filter while the hold feature ensures spatial simultaneity of corresponding detectors in each telescope. After completion of sampling by the multiplexer, all channel hold circuits are reset to ensure independence of data samples. The IRTM analog signals, which have a range of +/- 6V, are digitized by the analog-to-pulse width converter and flight data subsystem (FDS) counter into +/- 2**9 levels, yielding 1023 data numbers (DN) which are nearly linear with radiance in each channel. The IRTM multiplexer consists of sixty-eight FET switches and a buffer signal amplifier. In addition to thirty-two data channels (twenty-eight active and four spare), thirty-two channels of engineering data are also sample. These include eight temperature measurements from thermisters located at four locations on the reference plate, the electronics module, and each of the three ir detector packages (telescopes A, B, C). Three power supply voltages and the pre-dc restore voltage of twenty-one channels (telescopes A, B, and C) are monitored. The pre-dc restore monitors are diagnostic to determine the presence of large thermal or detector offsets. The scan mirror is driven by a four-position stepper motor through a 50/1 gear reduction. A motor drive pulse duration of 40 msec allows a 90 degree mirror rotation in 2 sec. The mirror position is sensed by a two-bit encoder on the motor shaft; the contacts at the three desired positions are about half of the width of 1.8 degree mirror step. The motor stepping is controlled by the FDS using a comparison of the encoder readout with the desired position originating either from the FDS normal mode clock or direct ground command; the motor cannot be directly commanded. In addition to the restore which occurs automatically in the normal model when the mirror reaches the space position, restores can be ground commanded when the IRTM is in the fixed planet or fixed space mode; in either case housekeeping data are multiplexed into the data stream during the 1-sec restore period. Whenever the mirror reaches the reference position, the calibration lamp is turned on for the next two integration periods. The lamp is at full radiance throughout the second integration period, which is used for gain determination of the D telescope channels. In the fixed reference mode, science and housekeeping data are sampled alternatively. Instrument Filter 'A - T20' =========================== Filter Name : T20 Filter Type : RESTSTRAHLEN Minimum Wavelength : 17.700000 Maximum Wavelength : 30.000000 Center Filter Wavelength : 21.000000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'B - T11' =========================== Filter Name : T11 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 9.800000 Maximum Wavelength : 12.500000 Center Filter Wavelength : 11.200000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'C1 - T7' =========================== Filter Name : T7 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 6.100000 Maximum Wavelength : 8.300000 Center Filter Wavelength : 7.200000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'C2 - T9' =========================== Filter Name : T9 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 8.300000 Maximum Wavelength : 9.800000 Center Filter Wavelength : 9.000000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'C3 - T15' ============================ Filter Name : T15 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 14.560000 Maximum Wavelength : 15.410000 Center Filter Wavelength : 15.000000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the plant port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Filter 'D - SOLAR UV-22' =================================== Filter Name : SOLAR UV-22 Filter Type : MULTILAYER INTERFERENCE Minimum Wavelength : 0.300000 Maximum Wavelength : 3.000000 Center Filter Wavelength : 1.600000 Description ----------- Relative spectral response of all channels was measured end to end using a Perkin-Elmer 16 U monochrometer with appropriate gratings and order filters. A globar at 1400 K was used in the 2-25 micrometer range; shortward of 2.0 micrometers a tungsten source at 2700 K was used. The reference detector was a thermocouple for all but the 0.4-1.1 micrometer range, where a calibrated silicon photodiode was used. Out-of-band measurements were made by replacing the spectrometer grating with a plane mirror and ir materials having known cutoff and cuton wavelengths. Flux calibration of the IRTM was performed under a simulated space environment using a vacuum chamber operated typically at a pressure of 1.E-6 Torr. The IRTM was operated by means of a console which simulated the interfaces and functions of the spacecraft FDS. A minicomputer was used to provide all operational sequences and modes. Data were recorded on magnetic tape for subsequent computer processing. The calibration fixture consisted of two identical blackbodies, one located in front of the space port and maintained at liquid nitrogen temperature and the other in front of the planet port and adjustable in temperature from 77 K to 350K; eleven settings from 140 K to 330 K were used. Blackbody temperatures were measured with platinum resistance thermometers having an absolute accuracy of +/- 0.1 degrees C. traceable to the National Bureau of Standards. The digitizer used in the test console provided ten times the resolution of the FDS digitizer, thus making the digitizing uncertainty during calibration insignificant compared to the noise. The calibration data thus produced are IRTM output in digitization level (DN) as a function of blackbody temperature. Radiometrically measured internal reference surface temperatures showed close agreement (+/- 0.5 degrees C.) with those measured independently with a thermister. The IRTM temperature was controlled by regulating the temperature of a mounting base plate and the thermal shield inside the vacuum chamber. Calibration was performed at 10 degrees C. spacing across the range of operating temperatures expected during flight. Typical IRTM channel response to scene brightness temperatures is shown in Fig. 8 of CHASE_ETAL_1978. The one-sample noise on the thermal channels is less than 1 DN except for the 15 micrometer channel where it is about 2.5 DN. The dynamic ranges of the surface thermal bands are based on temperatures expected for the Martian surface. The 300 K maximum chosen for the A telescope might be exceeded by midday summer temperatures, but temperatures above the 310-K limit of the B telescope should not be exceeded unless active volcanic areas were found; temperatures to 320 K and 330 K could be measured by the 9 micrometer and 7 micrometer bands. The 15 micrometer band dynamic range was set quite large as its resolution is noise limited rather than digitization limited. Instrument Optics 'A' ===================== Telescope Diameter : 0.058000 Telescope F Number : 3.500000 Telescope Focal Length : 0.203000 Telescope Resolution : 0.005100 Telescope T Number : UNK Telescope Transmittance : UNK Description ----------- The A telescope (17.7-24 micrometer) is shown schematically in Fig. 3 of CHASE_ETAL_1978. It is an f/3.5, 20.3-cm focal length Cassegrainian design with an aperture diameter of 5.8-cm., spherical surfaces, and, except for mirror materials, is identical to the B and C telescopes. By using relatively slow fore optics, degradation of filter sharpness normally caused by operating an interference filter in a low f-number beam is negligible. The focal plane contains a field-defining aperture plate with seven 0.107-cm diameter holes arranged in a chevron pattern. The fields of view thus defined are nested with those of the MAWD and imaging systems (Fig. 4 of CHASE_ETAL_1978). Behind each hole in the field stop plate is a lens which produces a 0.0254-cm diam image of the telescope aperture on the detector, which itself is about the same size. The final optical speed at the detector is f/1. Optical materials used in the four telescopes are shown in Table II, and the resulting spectral response is shown in Fig. 5 of CHASE_ETAL_1978. Mirrors are made of hot-pressed uncoated zinc oxide for both primary and secondary mirrors. The reststrahlen reflection properties of ZnO are the major factors in the A telescope spectral response. Minimizing extrafield sensitivity (EFS) was an important aspect of the optical design since on previous Mariner radiometers EFS contribution seriously compromised observations of scenes near large temperature contrasts (points near the planetary limb and polar caps). During instrumentation development, IRTM image quality was determined in two angular regions. In the near-field region, a laboratory collimator and ir source were used to measure the 2-D spatial response out to 16-mrad diam (three fields of view). Point source field of view measurements in this region are shown in Fig. 6 of CHASE_ETAL_1978. For far field measurements, sensitivity constraints dictated an approach in which the fraction of energy within a given angular annulus is measured. A 30.5-cm diam, concentric grooved, blackbody plate with a series of restricting apertures was used at several distances (30.5-cm, 140-cm, and 610-cm) to define angular response regions from about one field of view out to 1-rad diam. That is, with the telescope focused at 610-cm, a disk 3.17-cm in diameter at that distance defines one half-response field of view (5.2 mrad). The source was held at 95 degrees C. by a heater/regulator and integral water jacket. To prevent difficulties with atmospheric transmission, the entire apparatus was contained in a polyethylene bag flushed with dry N2. The EFS problem was more severe for the longer wavelength A telescope than the others, possibly owing to the higher reflectance at longer wavelengths of the black paint used inside the telescope. Tests using this apparatus led to several telescope modifications designed to reduce EFS (see Fig. 3 of CHASE_ETAL_1978): (1) A postfocal baffle was placed between the field lens and the detectors to confine energy to the sensitive area of the detectors. (2) A spider baffle, added to the outer edges of the secondary mirror support spider, was designed to reduce reflection off the sides of the spider legs. (3) A cone baffle coated with CTL 15 black paint was placed on the central dead spot of the secondary mirror. This was designed to prevent focal plane reflections from falling on the detectors. Of these three modifications, only the cone baffle gave significant improvement, although all three were incorporated in the design. These results of the final EFS measurements are shown in Fig. 6 of CHASE_ETAL_1978. The calculated response due to diffraction and the measured values are shown. The integrated EFS response between 12 mrad and 1-rad diam was about 4%. Of this, about 1/2 is due to diffraction effects. The effect of response outside of the nominal field of view can be estimated directly from data obtained on scans across the hot (subsolar) planetary limb. Assuming that the response is circularly symmetric, and all evidence indicates this to be closely followed, the signature of a half space would also be symmetric. A plot of fractional energy derived from a Viking 1 IRTM scan across the sunlit limb of Mars is shown in Fig. 6 of CHASE_ETAL_1978. The alignment was determined using a 20.3-cm (8-in.) collimator to illuminate all four telescopes with a small source of high temperature blackbody radiation. Measurements were taken simultaneously in twenty-eight channels over a 1.5-mrad square grid pattern. For each channel, a parabolic ellipsoid was fit to data where the measured intensity was more than 10% of the peak intensity in that channel. The alignment of each telescope was ascertained by combining the center of response so determined for the seven channels in the telescope. This procedure allowed for the alignment of the four telescopes to be determined with an estimated precision of 0.1 mrad. The back of the secondary mirror of the B telescope was aluminized and used as the alignment reference for this procedure and for instrument alignment on the spacecraft. The instrument pointing direction was verified in the same manner just prior to planetary encounter using Mars as a 5-mrad diam source and using the science platform motion to generate a 5-mrad spaced grid. The in-flight alignment is shown in Fig. 4 of CHASE_ETAL_1978. Instrument Optics 'B' ===================== Telescope Diameter : 0.058000 Telescope F Number : 3.500000 Telescope Focal Length : 0.203000 Telescope Resolution : 0.005100 Telescope T Number : UNK Telescope Transmittance : UNK Description ----------- The A telescope (17.7-24 micrometer) is shown schematically in Fig. 3 of CHASE_ETAL_1978. It is an f/3.5, 20.3-cm focal length Cassegrainian design with an aperture diameter of 5.8-cm., spherical surfaces, and, except for mirror materials, is identical to the B and C telescopes. By using relatively slow fore optics, degradation of filter sharpness normally caused by operating an interference filter in a low f-number beam is negligible. The focal plane contains a field-defining aperture plate with seven 0.107-cm diameter holes arranged in a chevron pattern. The fields of view thus defined are nested with those of the MAWD and imaging systems (Fig. 4 of CHASE_ETAL_1978). Behind each hole in the field stop plate is a lens which produces a 0.0254-cm diam image of the telescope aperture on the detector, which itself is about the same size. The final optical speed at the detector is f/1. Optical materials used in the four telescopes are shown in Table II, and the resulting spectral response is shown in Fig. 5 of CHASE_ETAL_1978. The B mirror is made of aluminized and SiO overcoated fused silica. The spectral bandpass of the ir channel is determined by interference bandpass filter and an AR coated detector lense. The out-of-band response for the B telescope is less than 0.1% of full scale for an object of 1.E-6 the radiance of a 5800-K blackbody, the level expected for reflectance from the subsolar region of Mars. Minimizing extrafield sensitivity (EFS) was an important aspect of the optical design since on previous Mariner radiometers EFS contribution seriously compromised observations of scenes near large temperature contrasts (points near the planetary limb and polar caps). During instrumentation development, IRTM image quality was determined in two angular regions. In the near-field region, a laboratory collimator and ir source were used to measure the 2-D spatial response out to 16-mrad diam (three fields of view). Point source field of view measurements in this region are shown in Fig. 6 of CHASE_ETAL_1978. For far field measurements, sensitivity constraints dictated an approach in which the fraction of energy within a given angular annulus is measured. A 30.5-cm diam, concentric grooved, blackbody plate with a series of restricting apertures was used at several distances (30.5-cm, 140-cm, and 610-cm) to define angular response regions from about one field of view out to 1-rad diam. That is, with the telescope focused at 610-cm, a disk 3.17-cm in diameter at that distance defines one half-response field of view (5.2 mrad). The source was held at 95 degrees C. by a heater/regulator and integral water jacket. To prevent difficulties with atmospheric transmission, the entire apparatus was contained in a polyethylene bag flushed with dry N2. Tests using this apparatus led to several telescope modifications designed to reduce EFS (see Fig. 3 of CHASE_ETAL_1978): (1) A postfocal baffle was placed between the field lens and the detectors to confine energy to the sensitive area of the detectors. (2) A spider baffle, added to the outer edges of the secondary mirror support spider, was designed to reduce reflection off the sides of the spider legs. (3) A cone baffle coated with CTL 15 black paint was placed on the central dead spot of the secondary mirror. This was designed to prevent focal plane reflections from falling on the detectors. Of these three modifications, only the cone baffle gave significant improvement, although all three were incorporated in the design. These results of the final EFS measurements are shown in Fig. 6 of CHASE_ETAL_1978. The calculated response due to diffraction and the measured values are shown. The integrated EFS response between 12 mrad and 1-rad diam was about 4%. Of this, about 1/2 is due to diffraction effects. The effect of response outside of the nominal field of view can be estimated directly from data obtained on scans across the hot (subsolar) planetary limb. Assuming that the response is circularly symmetric, and all evidence indicates this to be closely followed, the signature of a half space would also be symmetric. A plot of fractional energy derived from a Viking 1 IRTM scan across the sunlit limb of Mars is shown in Fig. 6 of CHASE_ETAL_1978. The alignment was determined using a 20.3-cm (8-in.) collimator to illuminate all four telescopes with a small source of high temperature blackbody radiation. Measurements were taken simultaneously in twenty-eight channels over a 1.5-mrad square grid pattern. For each channel, a parabolic ellipsoid was fit to data where the measured intensity was more than 10% of the peak intensity in that channel. The alignment of each telescope was ascertained by combining the center of response so determined for the seven channels in the telescope. This procedure allowed by the alignment of the four telescopes to be determined with an estimated precision of 0.1 mrad. The back of the secondary mirror of the B telescope was aluminized and used as the alignment reference for this procedure and for instrument alignment on the spacecraft. The instrument pointing direction was verified in the same manner just prior to planetary encounter using Mars as a 5-mrad diam source and using the science platform motion to generate a 5-mrad spaced grid. The in-flight alignment is shown in Fig. 4 of CHASE_ETAL_1978. Instrument Optics 'C' ===================== Telescope Diameter : 0.058000 Telescope F Number : 3.500000 Telescope Focal Length : 0.203000 Telescope Resolution : 0.005100 Telescope T Number : UNK Telescope Transmittance : UNK Description ----------- The A telescope (17.7-24 micrometer) is shown schematically in Fig. 3 of CHASE_ETAL_1978. It is an f/3.5, 20.3-cm focal length Cassegrainian design with an aperture diameter of 5.8-cm., spherical surfaces, and, except for mirror materials, is identical to the B and C telescopes. The focal plane contains a field-defining aperture plate with seven 0.107-cm diameter holes arranged in a chevron pattern. The fields of view thus defined are nested with those of the MAWD and imaging systems (Fig. 4 of CHASE_ETAL_1978). Behind each hole in the field stop plate is a lens which produces a 0.0254-cm diam image of the telescope aperture on the detector, which itself is about the same size. The final optical speed at the detector is f/1. Optical materials used in the four telescopes are shown in Table II, and the resulting spectral response is shown in Fig. 5 of CHASE_ETAL_1978. Mirrors are made of aluminized and SiO overcoated fused silica except for the A telescope, which uses hot-pressed uncoated zinc oxide for both primary and secondary mirrors. The spectral bandpass of the other ir channels is determined by interference bandpass filters and AR coated detector lenses. The out-of-band response for the B and C telescopes is less than 0.1% of full scale for an object of 1.E-6 the radiance of a 5800-K blackbody, the level expected for reflectance from the subsolar region of Mars. The A band has less than 0.1% response for wavelengths less than 16 micrometer, and wavelengths longer than 30 micrometer are limited by the Irtran 6 field lens. Minimizing extrafield sensitivity (EFS) was an important aspect of the optical design since on previous Mariner radiometers EFS contribution seriously compromised observations of scenes near large temperature contrasts (points near the planetary limb and polar caps). During instrumentation development, IRTM image quality was determined in two angular regions. In the near-field region, a laboratory collimator and ir source were used to measure the 2-D spatial response out to 16-mrad diam (three fields of view). Point source field of view measurements in this region are shown in Fig. 6 of CHASE_ETAL_1978. For far field measurements, sensitivity constraints dictated an approach in which the fraction of energy within a given angular annulus is measured. A 30.5-cm diam, concentric grooved, blackbody plate with a series of restricting apertures was used at several distances (30.5-cm, 140-cm, and 610-cm) to define angular response regions from about one field of view out to 1-rad diam. That is, with the telescope focused at 610-cm, a disk 3.17-cm in diameter at that distance defines one half-response field of view (5.2 mrad). The source was held at 95 degrees C. by a heater/regulator and integral water jacket. To prevent difficulties with atmospheric transmission, the entire apparatus was contained in a polyethylene bag flushed with dry N2. Tests using this apparatus led to several telescope modifications designed to reduce EFS (see Fig. 3 of CHASE_ETAL_1978): (1) A postfocal baffle was placed between the field lens and the detectors to confine energy to the sensitive area of the detectors. (2) A spider baffle, added to the outer edges of the secondary mirror support spider, was designed to reduce reflection off the sides of the spider legs. (3) A cone baffle coated with CTL 15 black paint was placed on the central dead spot of the secondary mirror. This was designed to prevent focal plane reflections from falling on the detectors. Of these three modifications, only the cone baffle gave significant improvement, although all three were incorporated in the design. These results of the final EFS measurements are shown in Fig. 6 of CHASE_ETAL_1978. The calculated response due to diffraction and the measured values are shown. The integrated EFS response between 12 mrad and 1-rad diam was about 4%. Of this, about 1/2 is due to diffraction effects. The effect of response outside of the nominal field of view can be estimated directly from data obtained on scans across the hot (subsolar) planetary limb. Assuming that the response is circularly symmetric, and all evidence indicates this to be closely followed, the signature of a half space would also be symmetric. A plot of fractional energy derived from a Viking 1 IRTM scan across the sunlit limb of Mars is shown in Fig. 6 of CHASE_ETAL_1978. The alignment was determined using a 20.3-cm (8-in.) collimator to illuminate all four telescopes with a small source of high temperature blackbody radiation. Measurements were taken simultaneously in twenty-eight channels over a 1.5-mrad square grid pattern. For each channel, a parabolic ellipsoid was fit to data where the measured intensity was more than 10% of the peak intensity in that channel. The alignment of each telescope was ascertained by combining the center of response so determined for the seven channels in the telescope. This procedure allowed by the alignment of the four telescopes to be determined with an estimated precision of 0.1 mrad. The back of the secondary mirror of the B telescope was aluminized and used as the alignment reference for this procedure and for instrument alignment on the spacecraft. The instrument pointing direction was verified in the same manner just prior to planetary encounter using Mars as a 5-mrad diam source and using the science platform motion to generate a 5-mrad spaced grid. The in-flight alignment is shown in Fig. 4 of CHASE_ETAL_1978. Instrument Optics 'D' ===================== Telescope Diameter : 0.037000 Telescope F Number : 5.500000 Telescope Focal Length : 0.203000 Telescope Resolution : UNK Telescope T Number : UNK Telescope Transmittance : UNK Description ----------- The D telescope has a reduced aperture of 3.7 cm and a focal length of f/5.5. By using relatively slow fore optics, degradation of filter sharpness normally caused by operating an interference filter in a low f-number beam is negligible. The focal plane contains a field-defining aperture plate with seven 0.107-cm diam holes arranged in a chevron pattern. The fields of view thus defined are nested with those of the MAWD and imaging systems (Fig. 4 of CHASE_ETAL_1978). Behind each hole in the field stop plate is a lens which produces a 0.0254-cm diam image of the telescope aperture on the detector, which itself is about the same size. The final optical speed at the detector is f/1. Optical materials used in the four telescopes are shown in Table II, and the resulting spectral response is shown in Fig. 5 of CHASE_ETAL_1978. Mirrors are made of aluminized and SiO overcoated fused silica except for the A telescope, which uses hot-pressed uncoated zinc oxide for both primary and secondary mirrors. The spectral bandpass of the other ir channels is determined by interference bandpass filters and AR coated detector lenses. The transmission elements of the D telescope insure that it is thermally blind. Special coatings on the D telescope mirrors were used to obtain a reasonably gray response to solar radiation. Minimizing extrafield sensitivity (EFS) was an important aspect of the optical design since on previous Mariner radiometers EFS contribution seriously compromised observations of scenes near large temperature contrasts (points near the planetary limb and polar caps). During instrumentation development, IRTM image quality was determined in two angular regions. In the near-field region, a laboratory collimator and ir source were used to measure the 2-D spatial response out to 16-mrad diam (three fields of view). Point source field of view measurements in this region are shown in Fig. 6 of CHASE_ETAL_1978. For far field measurements, sensitivity constraints dictated an approach in which the fraction of energy within a given angular annulus is measured. A 30.5-cm diam, concentric grooved, blackbody plate with a series of restricting apertures was used at several distances (30.5-cm, 140-cm, and 610-cm) to define angular response regions from about one field of view out to 1-rad diam. That is, with the telescope focused at 610-cm, a disk 3.17-cm in diameter at that distance defines one half-response field of view (5.2 mrad). The source was held at 95 degrees C. by a heater/regulator and integral water jacket. To prevent difficulties with atmospheric transmission, the entire apparatus was contained in a polyethylene bag flushed with dry N2. The EFS problem was more severe for the longer wavelength A telescope than the others, possibly owing to the higher reflectance at longer wavelengths of the black paint used inside the telescope. Tests using this apparatus led to several telescope modifications designed to reduce EFS (see Fig. 3 of CHASE_ETAL_1978): (1) A postfocal baffle was placed between the field lens and the detectors to confine energy to the sensitive area of the detectors. (2) A spider baffle, added to the outer edges of the secondary mirror support spider, was designed to reduce reflection off the sides of the spider legs. (3) A cone baffle coated with CTL 15 black paint was placed on the central dead spot of the secondary mirror. This was designed to prevent focal plane reflections from falling on the detectors. Of these three modifications, only the cone baffle gave significant improvement, although all three were incorporated in the design. These results of the final EFS measurements are shown in Fig. 6 of CHASE_ETAL_1978. The calculated response due to diffraction and the measured values are shown. The integrated EFS response between 12 mrad and 1-rad diam was about 4%. Of this, about 1/2 is due to diffraction effects. The effect of response outside of the nominal field of view can be estimated directly from data obtained on scans across the hot (subsolar) planetary limb. Assuming that the response is circularly symmetric, and all evidence indicates this to be closely followed, the signature of a half space would also be symmetric. A plot of fractional energy derived from a Viking 1 IRTM scan across the sunlit limb of Mars is shown in Fig. 6 of CHASE_ETAL_1978. The alignment was determined using a 20.3-cm (8-in.) collimator to illuminate all four telescopes with a small source of high temperature blackbody radiation. Measurements were taken simultaneously in twenty-eight channels over a 1.5-mrad square grid pattern. For each channel, a parabolic ellipsoid was fit to data where the measured intensity was more than 10% of the peak intensity in that channel. The alignment of each telescope was ascertained by combining the center of response so determined for the seven channels in the telescope. This procedure allowed by the alignment of the four telescopes to be determined with an estimated precision of 0.1 mrad. The instrument pointing direction was verified in the same manner just prior to planetary encounter using Mars as a 5-mrad diam source and using the science platform motion to generate a 5-mrad spaced grid. The in-flight alignment is shown in Fig. 4 of CHASE_ETAL_1978. Instrument Mode 'FIXED PLANET' ============================== Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperatureand a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. In the FIXED PLANET mode, the first 0,2, or 4 ICKs could be housekeeping data while the mirror was in motion to the planet position. Thereafter the instrument reported planet data untill the next command was received. Instrument Mode 'FIXED REFERENCE' ================================= Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperatureand a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. In the FIXED REFERENCE mode, the mirror was commanded to the reference position; 0 to 5 ICKS of housekeeping data were possible while the mirror was in motion. Thereafter, the instrument reported radiance readings or housekeeping data on alternate ICKs untill the next command was received. Instrument Mode 'FIXED SPACE' ============================= Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperatureand a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. In the FIXED SPACE mode, the mirror was commanded to the space position from wherever it had been, with 2 ICKs of housekeeping data if the mirror was not already in the space position. Thereafter the instrument reported space data until another command was received. Instrument Mode 'MODIFIED NORMAL' ================================= Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperatureand a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. A MODIFIED normal mode was also available, in which the only space view was the first of the cycle, followed by 243 ICKs of planet data. In NORMAL mode, ICKs 1 and 2 were housekeeping data while the mirror moved to space. ICK 3 was the space level before reset. During ICK 4, the electronics for all channels were reset so that the sensed radiance (meant to be the cosmic background level of essentially zero radiance) yielded a data number (DN) of a few. There was a filter on the reset so that the voltage change was only about 2/3 of the way to the space radiance level; this smoothed out the zero setting, but also meant that several cycles were required to recover from a serious drift. ICK 5 was still in the space position and yielded the DN response to space. Ick 6 and 7 were housekeeping data while the mirror moved to the reference position. ICK 8 and 9 were the DN response to the reference surface; only the second reading was used in calibration of the solar channel to allow the lamp filament to warm up completely. ICKs 10 through 13 were housekeeping data while the mirror moved to the planet position. The 57 ICKs 14-64 were planet data. The 7 ICK cycle to space, with reset of the zero-radiance DN level in all channels, was repeated each 64 ICKs, beginning on ICKs 65, 129, and 193, with motion directly back to the planet position for another 57 ICKs of planet data. Instrument Mode 'NORMAL' ======================== Instrument Power Consumption : 6.000000 In sections ----------- IRTM Description ----------- Other than power on or power off, the only command options for the IRTM controlled the motion of the scan mirror. This mirror could be commanded to 3 positions, separated by 90 degrees; PLANET, SPACE, and REFERENCE. In the PLANET position, data were acquired in all 28 channels. In SPACE, the zero-radiance level was reset to near the bottom of the dynamic range. In the REFERENCE position, gain calibration data was obtained using both a grooved blackbody at ambient instrument temperature and a small lamp and hemispherical diffuser for the solar telescope. The REFERENCE position was also the 'safe' position, used when the instrument was turned off. The NORMAL mode sequenced the pointing to PLANET most of the time, with pointing to SPACE at intervals of 64 ICKs, and to REFERENCE at intervals of 256 ICKs. ICK is a one syllable acronym for 'incremental counter keeper' and represents 1.12 second duration, the basic time interval of IRTM operation. It required 2 ICKs for the mirror to move 90 degrees and settle; whenever the mirror was in motion the downlink data contained housekeeping information about instrument status and detector voltage levels. In NORMAL mode, ICKs 1 and 2 were housekeeping data while the mirror moved to space. ICK 3 was the space level before reset. During ICK 4, the electronics for all channels were reset so that the sensed radiance (meant to be the cosmic background level of essentially zero radiance) yielded a data number (DN) of a few. There was a filter on the reset so that the voltage change was only about 2/3 of the way to the space radiance level; this smoothed out the zero setting, but also meant that several cycles were required to recover from a serious drift. ICK 5 was still in the space position and yielded the DN response to space. Ick 6 and 7 were housekeeping data while the mirror moved to the reference position. ICK 8 and 9 were the DN response to the reference surface; only the second reading was used in calibration of the solar channel to allow the lamp filament to warm up completely. ICKs 10 through 13 were housekeeping data while the mirror moved to the planet position. The 57 ICKs 14-64 were planet data. The 7 ICK cycle to space, with reset of the zero-radiance DN level in all channels, was repeated each 64 ICKs, beginning on ICKs 65, 129, and 193, with motion directly back to the planet position for another 57 ICKs of planet data. Mounted On Platform 'SCAN PLATFORM' =================================== Cone Offset Angle : 0.040000 Cross Cone Offset Angle : -0.060000 Description ----------- OFFSET ANGLE SCALED FROM FIGURE 4 OF CHASE_ETAL_1978; these were determined by scans across Mars during approach, when the angular diameter of the planet was 1.93 and 4.79 milliradians (VO-1)