urn:nasa:pds:context:instrument:nirs.hay 1.0 1.7.0.0 Product_Context 2016-10-01 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model urn:nasa:pds:context:instrument_host:spacecraft.hay::1.0 instrument_to_instrument_host Abe, S., T. Mukai, N. Hirata, O.S. Barnouin-Jha, A.F. Cheng, and 11 others, Near-infrared spectral results of asteroid Itokawa from the Hayabusa spacecraft, Science 312, 1334-1338, 2006. reference.ABEETAL2006 Abe, S., T. Mukai, N. Hirata, O.S. Barnouin-Jha, A.F. Cheng, H. Demura, R.W. Gaskell, T. Hashimoto, K. Hiraoka, T. Honda, T. Kubota, M. Matsuoka, T. Mizuno, R. Nakamura, D.J. Scheeres, and M. Yoshikawa, Mass and Local Topography Measurements of Itokawa by Hayabusa, Science, 312, 1344-1347, 2006. reference.ABEETAL2006B Fujiwara, A., T. Mukai, J. Kawaguchi, and K.T. Uesugi, Sample Return Mission to NEA : MUSES-C. Advances in Space Research 25, 231-238, 2000. reference.FUJIWARAETAL2000 Kitazato, K., B.E. Clark, M. Abe, S. Abe, Y. Takagi, T. Hiroi, O.S. Barnouin-Jha, P.A. Abell, S.M. Lederer, F. Vilas, Near-infrared spectrophotometry of Asteroid 25143 ltokawa from NIRS on the Hayabusa spacecraft, Icarus 194, 137-145, 2008. reference.KITAZATOETAL2008 NEAR-INFRARED SPECTROMETER Spectrometer not applicable not applicable The following information is taken from Kitazato et al. (2008) and Abe et al. (2010) (Unpublished). Instrument Overview =================== The Hayabusa Near-Infrared Spectrometer (NIRS) is composed of a grating infrared spectrometer (N1RS-S), a spectrometer electronics (NIRS-E) and a data processing unit to control NIRS, which is also used to operate the Hayabusa XRS. The NIRS-S is mounted on -Y panel inside surface of the spacecraft chassis in such a way that the viewing is fixed in almost the spacecraft Z-axis, direction in which opposite the solar arrays and high-gain antenna (see Fujiwara et al., 2000). The NIRS optical design consists of an entrance aperture stop, a field stopslit, two mirrors, a diffraction grating, a camera lens assembly, a detector, and two calibration targets. The assembled spectrometer is covered with carbon-fiber reinforced plastic box case (300x150x100mm in size). After passing through the slit, incident light is dispersed by a grism transmission diffraction grating, combined with a cross disperser and re-imaged by camera optics. The first-order light falls on a 64-element indium-gallium-arsenide (1nGaAs) linear detector array that covers the range of 750-2250 nm in increments of 24 nm. The cross disperser prevents light other than first-order from reaching the detector. NIRS carries the two types of onboard calibration targets, an incandescent halogen lamp and a light-emitting-diode (LED), for periodic monitoring of detector stability. These targets are mounted on the aperture plate. The design was developed in accordance with the requirements of downsizing and weight saving. Table 1 lists key specifications and characteristics of the instrument. Note that the calibration LED is fixed outside of the aperture but the lamp is fixed on the inner edge of the aperture so that the effective aperture size drops off by 4 percent. The slit size was determined to provide an angular field-of-view (FOV) of 0.1 x 0.1 degrees, which corresponds to a spatial resolution of 17 x 17 meters at a distance of 10 km. A moveable shutter can be used to block the slit completely for dark current measurements. The signal in a dark spectrum represents the background electronic and other noise inherent in the instrument. A thermoelectric Peltier device actively cools the InGaAs detector arrays in order to achieve a sufficient signal-to-noise ratio (SNR). The detector has a built-in complementary metal oxide semiconductor (CMOS) image sensor, which is used to multiplex the outputs to a single analog to digital (A/D) converter. Table 1: NIRS Specifications ----------------------------------------------------- Characteristic Value ----------------------------------------------------- Spectral range 850 - 2100 nm Spectral resolution 24 nm/channel Detector element size 30 x 100 microns Number of detector elements 64 Grating ruling 75 grooves/mm Slit size 70 x 70 microns Field of view 0.1 x 0.1 degrees Aperture 27.2 mm Imaging interval 65.536 ms Integration time 0.256 - 57.344 ms Shutter driving 7.63 Hz (131.072 ms) Size (NIRS-S) 336 x 165 x 100 mm Mass (NIRS-S) 1.53 kg Power (NIRS-S) 9.50 W Power (NIRS-E) 0.45 W ------------------------------------------------------ Operating Modes and Data Acquisition ==================================== NIRS operation modes are implemented in the onboard software using instrument parameters that can be changed by ground operation commands. There are a total of five modes available to NIRS; NORMAL, RAW, HIST, LIDAR, and FLASH. In the NORMAL mode, each observation consists of certain sequential sets of alternate light and dark frames. That is accomplished by the chopping motion of the shutter, allowing the dark current level of the detector to be subtracted on a channel-by-channel basis every time. The CMOS image sensor serves to read differences of outputs on each detector element between light and dark frames. The NIRS frame length is 65.536 ms, which corresponds to half of the shutter driving cycle, and exposure time can be changed at 256-stage from 0.256 ms to 57.344 ms. In addition, the number of stacked light-dark frames can be also changed from 1 to 2 to the 255th power as the n-th power of two. Most of NIRS data were taken in this mode. The basic unit of spectral data for any given NIRS channel is digital number (DN) showing the integrated photon counts during a setting exposure-time interval. The raw data are originally sampled with 14 bits per channel (0-16383 DNs). A DN has a value of approximately 0.565 mV output from the detector pre-amplifiers when at gain 1.08x. In the NORMAL mode, the data averaging of light frames subtracted dark spectrum are operated with onboard software, and only the mean, standard deviation, maximum and minimum of the DNs at individual channels were downloaded in instrument telemetry. The RAW mode prohibits the data averaging on board the spacecraft. The HIST mode provides a sequential output of the housekeeping (HK) data for NIRS. However, the RAW and HIST modes have not been used in reality until the completion of the asteroid observation. The LIDAR and FLASH modes were supposed to be used in the descent and touchdown phase during the Hayabusa rendezvous with ltokawa. In the LIDAR mode, NIRS carries out the frame difference readout in sync with the periodic laser pulse of LIDAR (a laser ranging instrument on Hayabusa) so as to observe the reflected laser light of the LIDAR from the asteroid surface. The shutter stays open during this observation mode. On the other hand, the FLASH mode was designed to remove the frame contaminated by flashlights to irradiate target markers for autonomous navigation of sampling. This mode is identical to the NORMAL mode, excluding the removal of the synchronized frame with flashlights. Pre-launch Calibration and Characterization =========================================== The NIRS instrument was tested and calibrated extensively at the piece-part and instrument levels to verify its performance and to define its operational characteristics to levels required to meet the science objectives. The tests and calibrations were carried out at ambient and vacuum chamber conditions. Also the instrument underwent extensive vibrational and thermal vacuum testing. The ground testing and calibrations of NIRS were conducted primarily at the Institute of Space and Astronautical Science (ISAS), Japan. The tests at the piece-part level included measurements of detector linearity, responsivity as functions of wavelength and temperature, dark current characteristics and spectral transmission properties of the grating. Instrument-level calibrations of NIRS included measurements of the responsivity as a function of wavelength and FOV of each detector element (to verify detector linearity and alignment and to yield spectral resolution, spatial resolution, and flux calibration data), characterization of dark current levelsfor each detector element as a function of temperature, characterization of the level of spectral crosstalk on detector channels, and electronic performance characteristics of the detector arrays. Finally, measurements of the calibration targets and some of mineral and rock samples were made with the assembled NIRS instrument. The NIRS calibrations show that the detectors are linear and well aligned and that the instrument operates at very close to its design parameters for spatial and spectral resolution. Spectral Calibration -------------------- Spectral calibration was conducted in order to establish the wavelengths sensed by a detector for each of the 64 possible grating positions. That was performed by illuminating the instrument aperture with the monochromator, which is used in conjunction with an incandescent source and an integrating sphere. The signals from the detector arrays were recorded with the monochromator wavelength scanned in 100 nm increments over the first-order wavelength range. The spectral calibration was performed under the ambient temperature of 2 degrees C. The central wavelength in nm of each of the detector arrays and the channel-to-wavelength relationship is expressed by lambda = -23.56n + 2271.44 where n is the channel nuniber between 1 to 64. The accuracy of this equation for linear fitting is approximately 2 nm. Although the full range of the N1RS detector array is 751.8 to 2259.7 nm, it is further limited, however, to 850 to 2100 nm (channels 7-60). The lower six channels (channels 1-6, at 2248-2130 nm) are near or in the detector cutoff, making the effective upper bound for good signal-to-noise ratio (SNR) around 2100 nm for the signal level expected at Itokawa. The upper four channels of the InGaAs detector (channels 61-64, at 834-763 nm) register very low signal due to fall-off in detector responsivity and grism efficiency. Radiometric Calibration ----------------------- Tilt radiometric response of the NIRS was determined in a number of tests by recording the detector response while viewing a laboratory calibrated field with a halogen lamp and a Spectralon reflectance target. The measurements used a 1 kW filament lamp with a quartz envelope containing halogen gas. The spectral radiance of this source has been calibrated by the Oriel Instruments and this calibration is directly traceable to the National Institute of Standards and Technology (NIST). The lamp was powered by regulated direct current at the prescribed amperage, measured using NIST-traceable instruments. In order to produce an extended source of known radiance, a Labsphere Spectralon standard, calibrated with traceability to NIST, was used. The response of the instrument was found to be linear and uncertainties of the NIRS absolute radiometric calibration of were estimated to be approximately 10 percent in the effective wavelength range. Though the calibration was performed under the ambient condition, we applied the correction of atmospheric water vapor using the MODTRAN software. The NIRS radiometric calibrations showed that for radiances expected at Itokawa, a signal-to-noise ratio (SNR) in excess of 100 is easily attainable in 57 InGaAs channels (from 2 to 58) with nominal detector temperature of -15 degrees C. Since the detector temperature was maintained in an almost constant value in flight, except for caltarget observations, no temperature correction is required for the radiometric calibration. Spatial Calibration ------------------- Alignment of the boresights of the Hayabusa scientific instruments relative to each other and to the nominal common boresight, the spacecraft -Z axis (the Z axis is perpendicular to the plane of Hayabusa's solar panels, and +Z direction on the spacecraft points toward the Sun with the spacecraft in its nominal orientation), were measured on ground, after spacecraft integration, using the reference optical cubes on each instrument For NIRS, the accurate boresight vector was found to be inclined toward the spacecraft -Z axis with the Euler angles (-0.1140, -0.0012, 0.0 degrees) and the co-alignment with LIDAR was verified. The FOV has rectangular shape with its sides along the X and Y axes of the instrument's frame and the angular size of 0.1 degrees. As these measurements were done under conditions of 1 gravity and room temperature, conditions experienced by Hayabusa in space will distort the coalipment between instruments slightly. Coalignment between the instruments was re-measured in flight and during the asteroid rendezvous. In-flight Calibration ===================== After launch, NIRS performed a comprehensive series of in-flight tests to validate and supplement ground calibration data, and to characterize instrument stability, pointing, and co-alignment with other instruments under flight conditions. The in-flight observations of astronomical targets took place during the cruise phase before the arriving at Itokawa, with NIRS obtaining spatially resolved spectra of the Earth and Moon, and disk-integrated spectra of the Mars, Jupiter, and Saturn, including three bright stars. Long-term Stability ------------------- The periodic onboard calibration-target observations in space assessed the long-term stability of radiometric and spectral characteristics. The onboard calibrated LED generates a narrow spectrum centered at the specific wavelength of 1.8 microns. Under a constant temperature condition, its peak wavelength does not shift beyond the NIRS spectral resolution. Without short-term general increases as in Earth swingby and the arrival, the calibration measurements show the gradual changes in NIRS channel responses up to +/- 3 percent. The reason for this behavior is probably related to spectral alignment of the detector. Using the data of detector wavelength drift, we found that displacement of detector channels can generate such changes in the detector responses. The general high responsivity seen in Earth swingby may be occurred by the lamp brightening due to the NIRS continuous operation. The rest of the overall time series corresponds to a gradual decay of the instrument primarily due to solar and cosmic ray radiation damage to the detectors and electronics. In addition, a general loss of 3-4 percent of NIRS response in the detector resulted from the launch. The slight changes in instrument sensitivity over two years of in-flight operations were found, but the radiometric response had been highly stable on time scale of a few months. The linearities of NIRS detector response also were verified from the various exposure-time frames on the calibration-target observation. Thus, we found that differences in instrument sensitivity of NIRS for the rendezvous phase fall within ~1 percent for overall effective detector channels. Validation of Calibration Coefficients -------------------------------------- Validation of the absolute calibration was performed through observations of the astronomical targets during the cruise. The spectra show an overall close match between the NIRS data and ground-based observations. Stray light from outside of the FOV was not a major issue with NIRS since it was not identified in the pre-launch test with a blackbody cavity. However, significant stray reflections were found when NIRS had observed across the limb of Moon. This may be due to the scattered light by the calibration lamp mounted on the aperture stop. The effect was dominant in the shorter wavelengths and required correction for proper calibration of the instrument. NIRS calibration did not incorporate a scattered light correction from pre-launch tests. The magnitude of out-of-field signal was quantified by acquiring swaths of spectra across the limb of Moon and Itokawa, during different orbits as the source of stray light changes in its size and illumination. These results will also be augmented by the results of the more controlled investigations of stray and scattered light conducted during pre-flight calibrations. The magnitude of the scattered light is less than ~7% as shown in Figure 8 of Abe et al. (2010), but its correction for the Itokawa spectral data has not been performed yet. At wavelengths > 1 micron, the effect of the scattered light is small compared with reflected light from Itokawa's surface. As for NIRS alignment and pointing, the co-alignment of NIRS with the AM1CA and with respect to the spacecraft was determined from the simultaneous observations of bright stars as point sources. The other observation was attained during the Itokawa rendezvous phase. The NIRS had detected the reflected laser light of the LIDAR from the asteroid surface during the spacecraft descent (Abe et al. 2006). The LIDAR generates a 1064-nm yttrium-aluminus-garnet-Nd (YAG-Nd) laser beam to measure distance by determining the time of flight for laser light to travel from the spacecraft to asteroid and return. The detected LIDAR spectra have shown the peak wavelength same as that obtained in prelaunch. Therefore, we found that there is no alteration of the NIRS spectral alignment from the prelaunch to final stage of the rendezvous phase. Moreover, L1DAR has a beam width of 0.04 degrees x 0.097 degrees, and such detection means that LIDAR boresight has been coaligned with NIRS as expected. References ========== Abe, M., Y. Takagi, K. Kitazato, S. Abe, T. Hiroi, F. Vilas, B.E. Clark, P.A. Abell, S.M. Lederer, K.S. Jarvis, T. Nimura, Y. Ueda, A. Fujiwara, Near-Infrared Spectral Results of Asteroid Itokawa from the Hayabusa Spacecraft, Science 312, 1334-1338, 2006. Abe, S., T. Mukai, N. Hirata, O.S. Barnouin-Jha, A.F. Cheng, H. Demura, R.W. Gaskell, T. Hashimoto, K. Hiraoka, T. Honda, T. Kubota, M. Matsuoka, T. Mizuno, R. Nakamura, D.J. Scheeres, M. Yoshikawa, Mass and Local Topography Measurements of Itokawa by Hayabusa. Science 312, 1344-1349, 2006. Abe, M., Y. Takagi, S. Abe, and K. Kitazato, Instrument calibration of the Hayabusa near-infrared spectrometer, Unpublished, 2010. (A copy of this paper may be found in the document directory of the NIRS calibrated data set, HAY-A-NIRS-3-NIRSCAL-V1.0.) Fujiwara, A., T. Mukai, J. Kawaguchi, and K.T. Uesugi, Sample Return Mission to NEA : MUSES-C. Advances in Space Research 25, 231-238, 2000. Kitazato, K., B.E. Clark, M. Abe, S. Abe, Y. Takagi, T. Hiroi, O.S. Barnouin-Jha, P.A. Abell, S.M. Lederer, F. Vilas, Near-infrared spectrophotometry of Asteroid 25143 ltokawa from NIRS on the Hayabusa spacecraft, Icarus 194, 137-145, 2008.