|
Instrument Information |
|
| IDENTIFIER | urn:nasa:pds:context:instrument:mawd.vo1::1.0 |
| NAME |
MARS ATMOSPHERIC WATER DETECTOR |
| TYPE |
SPECTROMETER |
| DESCRIPTION |
INSTRUMENT: MARS ATMOSPHERIC WATER DETECTOR
SPACECRAFT: VIKING ORBITER 1
Instrument Information
======================
Instrument Id : MAWD
Instrument Host Id : VO1
Pi Pds User Id : CBFARMER
Instrument Name : MARS ATMOSPHERIC WATER
DETECTOR
Instrument Type : UNK
Build Date : UNK
Instrument Mass : UNK
Instrument Length : UNK
Instrument Width : UNK
Instrument Height : UNK
Instrument Serial Number : UNK
Instrument Manufacturer Name : JET PROPULSION LABORATORY
Instrument Description
======================
This experiment was designed to measure the absorption of solar
radiation by the strong lines at the center of the 1.4
micrometer (7200 cm**-1) combination vibration-rotation bands
of water vapor. The MAWD instrument is a fixed grating
spectrometer having five channels centered on three absorption
lines and two continuum regions between these lines. All
channels utilize PbS detectors; the spectral resolution of each
is about 1.2 cm**-1. The instantaneous field of view (IFOV) of
the detectors is 0.96 by 0.12 degree. The IFOV can be
step-scanned perpendicular to its long dimension through
fifteen positions by a raster mirror incorporated in the
optical train. The time spent at each step (approximately the
signal integration time) is 280 milliseconds, and the duration
of the raster is 4.48 seconds. The combination of the motions
of the raster mirror, the orbiter scan platform, and the
orbital ground track generates sets of slew patterns over the
planet's surface. A basic description of the instrument, its
observational modes and its derived data products is given in
FARMER_ETAL_1977.
Science Objectives
==================
There are two major objectives of the Viking MAWD experiments.
The first of these is to map, during the far encounter and
preliminary orbital phases, the distribution of water vapor
over the planet, and in this way perform the vital initial
function of investigating prospective lading sites with respect
to this particular characteristic. The second objective is
concerned with the nature of the water vapor cycle itself and
the relationship between the martian atmospheric and surface or
subsurface water. To this end, the observations are designed
to investigate spatial, diurnal, and seasonal variations of
water vapor with high spatial and temporal resolutions. A
basic description of the instrument, its observational modes
and its derived data products is given in FARMER_ETAL_1977.
Operational Considerations
==========================
The MAWD instrument on Viking Orbiter 1 operated normally
throughout the mission.
Calibration Description
=======================
The precise frequency location of the various channels is
maintained against possible shifts due to thermal distortion of
the instrument's optical alignment by a monochromatic neon
reference system, using a set of silicon photodiodes as
detectors. Motion of the neon lamp exit plane image with
respect to the silicon reference detectors is sensed and used
to drive a cam which repositions the grating to preserve the
correct wavelength alignment. The channel responses are
corrected by means of periodic calibrations made by inserting a
mirror into the input beam so that the detectors view a
sunlight-illuminated diffusely reflecting plate mounted on a
structural member of the spacecraft.
Section 'MAWD'
==============
Total Fovs : 15
Data Rate : 280.000000
Sample Bits : 10
'MAWD' Detectors
----------------
CH1
CH2
CH3
CH4
CH5
'MAWD' Electronics
------------------
MAWD
'MAWD' Section Optic IDs
------------------------
MAWD
In modes
--------
NORMAL
WAVELENGTH SCANNING
'MAWD' Section FOV Shape 'RECTANGULAR'
--------------------------------------
Section Id : MAWD
Fovs : 15
Horizontal Pixel Fov : 0.120000
Vertical Pixel Fov : 0.960000
Horizontal Fov : 1.800000
Vertical Fov : 0.960000
'MAWD' Section Parameter 'RADIANCE CHANNEL 1'
---------------------------------------------
MAWD Channel 1 measured radiance per wave number at a
frequency of 7223.13 cm**-1.
Instrument Parameter Name : RADIANCE CHANNEL 1
Sampling Parameter Name : TIME
Instrument Parameter Unit : 10**-6 WATT / CM**-2 /
STERADIAN / W
Minimum Instrument Parameter : UNK
Maximum Instrument Parameter : UNK
Noise Level : UNK
Sampling Parameter Interval : 0.280000
Sampling Parameter Resolution : 0.280000
Sampling Parameter Unit : SECOND
'MAWD' Section Parameter 'RADIANCE CHANNEL 2'
---------------------------------------------
MAWD Channel 2 measured radiance per wave number at a
frequency of 7224.50 cm**-1.
Instrument Parameter Name : RADIANCE CHANNEL 2
Sampling Parameter Name : TIME
Instrument Parameter Unit : 10**-6 WATT / CM**-2 /
STERADIAN / W
Minimum Instrument Parameter : UNK
Maximum Instrument Parameter : UNK
Noise Level : UNK
Sampling Parameter Interval : 0.280000
Sampling Parameter Resolution : 0.280000
Sampling Parameter Unit : SECOND
'MAWD' Section Parameter 'RADIANCE CHANNEL 3'
---------------------------------------------
MAWD Channel 3 measured radiance per wave number at a
frequency of 7232.20 cm**-1.
Instrument Parameter Name : RADIANCE CHANNEL 3
Sampling Parameter Name : TIME
Instrument Parameter Unit : 10**-6 WATT / CM**-2 /
STERADIAN / W
Minimum Instrument Parameter : UNK
Maximum Instrument Parameter : UNK
Noise Level : UNK
Sampling Parameter Interval : 0.280000
Sampling Parameter Resolution : 0.280000
Sampling Parameter Unit : SECOND
'MAWD' Section Parameter 'RADIANCE CHANNEL 4'
---------------------------------------------
MAWD Channel 4 measured radiance per wave number at a
frequency of 7238.50 cm**-1.
Instrument Parameter Name : RADIANCE CHANNEL 4
Sampling Parameter Name : TIME
Instrument Parameter Unit : 10**-6 WATT / CM**-2 /
STERADIAN / W
Minimum Instrument Parameter : UNK
Maximum Instrument Parameter : UNK
Noise Level : UNK
Sampling Parameter Interval : 0.280000
Sampling Parameter Resolution : 0.280000
Sampling Parameter Unit : SECOND
'MAWD' Section Parameter 'RADIANCE CHANNEL 5'
---------------------------------------------
MAWD Channel 5 measured radiance per wave number at a
frequency of 7242.74 cm**-1.
Instrument Parameter Name : RADIANCE CHANNEL 5
Sampling Parameter Name : TIME
Instrument Parameter Unit : 10**-6 WATT / CM**-2 /
STERADIAN / W
Minimum Instrument Parameter : UNK
Maximum Instrument Parameter : UNK
Noise Level : UNK
Sampling Parameter Interval : 0.280000
Sampling Parameter Resolution : 0.280000
Sampling Parameter Unit : SECOND
Instrument Detector 'CH1'
=========================
Detector Type : PBS
Detector Aspect Ratio : 0.125000
Minimum Wavelength : 7215.130000
Maximum Wavelength : 7231.130000
Nominal Operating Temperature : 200.000000
Description
-----------
The PbS detectors are cooled to operating temperature by
being connected via a flexible copper strap to a plate
radiating to space. The normal operating frequency for
channel 1 (CH1) is 7223.13 cm**-1, with a frequency
resolution of 1.25 cm**-1.
Sensitivity
-----------
The PbS detector NEP (Noise Equivalent Power) is
approximately 3 x 10**-13 watt hz**-2. The D* (Detectivity)
is approximately 2.6 x 10**11 hz**-2 cm / watt. The SN
(signal to noise ratio) is 50 at a spectral irradiance of 3.5
x 10**-7 watt / wavenumber/ cm**2 / steradian.
Instrument Detector 'CH2'
=========================
Detector Type : PBS
Detector Aspect Ratio : 0.125000
Minimum Wavelength : 7216.500000
Maximum Wavelength : 7232.500000
Nominal Operating Temperature : 200.000000
Description
-----------
The PbS detectors are cooled to operating temperature by
being connected via a flexible copper strap to a plate
radiating to space. The normal operating frequency for
channel 2 (CH2) is 7224.50 cm**-1, with a frequency
resolution of 1.25 cm**-1.
Sensitivity
-----------
The PbS detector NEP (Noise Equivalent Power) is
approximately 3 x 10**-13 watt hz**-2. The D* (Detectivity)
is approximately 2.6 x 10**11 hz**-2 cm / watt. The SN
(signal to noise ratio) is 50 at a spectral irradiance of 3.5
x 10**-7 watt / wavenumber/ cm**2 / steradian.
Instrument Detector 'CH3'
=========================
Detector Type : PBS
Detector Aspect Ratio : 0.125000
Minimum Wavelength : 7224.200000
Maximum Wavelength : 7240.200000
Nominal Operating Temperature : 200.000000
Description
-----------
The PbS detectors are cooled to operating temperature by
being connected via a flexible copper strap to a plate
radiating to space. The normal operating frequency for
channel 3 (CH3) is 7232.20 cm**-1, with a frequency
resolution of 1.25 cm**-1.
Sensitivity
-----------
The PbS detector NEP (Noise Equivalent Power) is
approximately 3 x 10**-13 watt hz**-2. The D* (Detectivity)
is approximately 2.6 x 10**11 hz**-2 cm / watt. The SN
(signal to noise ratio) is 50 at a spectral irradiance of 3.5
x 10**-7 watt / wavenumber/ cm**2 / steradian.
Instrument Detector 'CH4'
=========================
Detector Type : PBS
Detector Aspect Ratio : 0.125000
Minimum Wavelength : 7230.500000
Maximum Wavelength : 7246.500000
Nominal Operating Temperature : 200.000000
Description
-----------
The PbS detectors are cooled to operating temperature by
being connected via a flexible copper strap to a plate
radiating to space. The normal operating frequency for
channel 4 (CH4) is 7238.50 cm**-1, with a frequency
resolution of 1.25 cm**-1.
Sensitivity
-----------
The PbS detector NEP (Noise Equivalent Power) is
approximately 3 x 10**-13 watt hz**-2. The D* (Detectivity)
is approximately 2.6 x 10**11 hz**-2 cm / watt. The SN
(signal to noise ratio) is 50 at a spectral irradiance of 3.5
x 10**-7 watt / wavenumber/ cm**2 / steradian.
Instrument Detector 'CH5'
=========================
Detector Type : PBS
Detector Aspect Ratio : 0.125000
Minimum Wavelength : 7236.740000
Maximum Wavelength : 7250.740000
Nominal Operating Temperature : 200.000000
Description
-----------
The PbS detectors are cooled to operating temperature by
being connected via a flexible copper strap to a plate
radiating to space. The normal operating frequency for
channel 5 (CH5) is 7242.74 cm**-1, with a frequency
resolution of 1.25 cm**-1.
Sensitivity
-----------
The PbS detector NEP (Noise Equivalent Power) is
approximately 3 x 10**-13 watt hz**-2. The D* (Detectivity)
is approximately 2.6 x 10**11 hz**-2 cm / watt. The SN
(signal to noise ratio) is 50 at a spectral irradiance of 3.5
x 10**-7 watt / wavenumber/ cm**2 / steradian.
Instrument Electronics 'MAWD'
=============================
Description
-----------
The signals from the five detectors are individually and
simultaneously amplified, synchronously demodulated, and
integrated for 280 milliseconds. After integration is
complete, the channels are sampled by the spacecraft data
system and digitized to 10-bit serial digital words for
transmission to Earth.
Instrument Optics 'MAWD'
========================
Telescope Diameter : 0.025000
Telescope F Number : 5.000000
Telescope Focal Length : UNK
Telescope Resolution : UNK
Telescope Serial Number : UNK
Telescope T Number : UNK
Telescope T Number Error : UNK
Telescope Transmittance : UNK
Description
-----------
Radiation from the planet is focused through a tuning fork
chopper onto the input slit of the instrument by a small (2.5
cm, f/5) input telescope which views the surface via an
external scanning mirror. The radiation is collimated by a
50 cm focal length parabolic mirror, then falls on a 12000
line per cm grating. The dispersed radiation is reimaged by
the collimating mirror onto the detectors, which are in the
same plane as the entrance slit. For a schematic, see Fig.
1 in FARMER_ETAL_1977.
Instrument Mode 'NORMAL'
========================
Data Path Type : UNK
Gain Mode Id : UNK
Instrument Power Consumption : UNK
In sections
-----------
MAWD
Description
-----------
In the normal data gathering mode, the grating is locked and
the channels are fixed at the desired wavelength locations.
The raster mirror steps through fifteen positions, scanning
the field of view of each detector across the planet's
surface.
Instrument Mode 'WAVELENGTH SCANNING'
=====================================
Data Path Type : UNK
Gain Mode Id : UNK
Instrument Power Consumption : UNK
In sections
-----------
MAWD
Description
-----------
In the wavelength scanning data gathering mode, the grating
is scanned through a small angular range to record the
continuous spectrum of the atmosphere. A range of 8 cm**-1
on either side of the normal (locked) position of each
channel is covered, giving a total composite spectrum
covering approximately 40 cm**-1. This mode was rarely used.
Mounted On Platform 'SCAN PLATFORM'
===================================
Cone Offset Angle : UNK
Cross Cone Offset Angle : UNK
Twist Offset Angle : UNK
Description
-----------
MAWD was mounted on the orbiter's scan platform, along with
the Infrared Thermal Mapper (IRTM) instrument and the Visual
Imaging Subsystem (VIS) cameras. The fields of view of all
three instruments overlap (see Fig. 1 in SNYDER_1977).
|
| MODEL IDENTIFIER | |
| NAIF INSTRUMENT IDENTIFIER |
not applicable |
| SERIAL NUMBER |
not applicable |
| REFERENCES |
Farmer, C.B., D.W. Davies, P.E. Doms, A.L. Holland,
and D.D. Laporte, Mars: Water Vapor Observations From
the Viking Orbiters, Journal of Geophysical Research,
82, 4225-4248, 1977. Snyder, C.W., The Missions of the Viking Orbiters, Journal of Geophysical Research, 82, 3971-3983, 1977. |
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