urn:nasa:pds:context:instrument:nis.near 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.near::1.0 instrument_to_instrument_host Acuna, M., C.T. Russell, L.J. Zanetti, and B.J. Anderson, The NEAR Magnetic Field Investigation: Science Objectives at Asteroid Eros 433 and Experimental Approach, Journal of Geophysical Research, Vol. 102(E10), pp. 23751-23760, 1997. reference.ACUNAETAL1997 unk reference.CHENG1997 Farquhar, R.W., D. Dunham, and J. McAdams, NEAR Mission Overview and Trajectory Design, Journal of Astronautical Science, Vol. 43, pp. 353-371, 1995. reference.FARQUHARETAL1995 Izenberg, N.R., K. Peacock, J. Warren, S.L. Murchie, and J.F. Bell III, In-flight calibration of NEAR's near infrared spectrometer, Proceedings of the 1998 SDL/USU Symposium on Infrared Radiometric Sensor Calibration, Space Dynamics Laboratory, Utah State University, Logan, UT, USA, 1998. reference.IZENBERGETAL1998 JHU/APL, NEAR Near Infrared Spectrograph/Magnetometer DPU Software Requirement Specification, JHU/APL pub. 7357-9001 Rev. A, JHU/APL Space Department, Laurel, MD, 1995. reference.NISAPLSRS1995 Peacock, K., Calibration of the Near Infrared Spectrograph, Proceedings of the 1997 SDL/USU Symposium on Infrared Radiometric Sensor Calibration, Space Dynamics Laboratory, Utah State University, Logan, UT, USA, 1997. reference.PEACOCK1997 Trombka, J.I., W.V. Boynton, J. Bruckner, S.W. Squyres, P.E. Clark, R. Starr, L.G. Evans, S.R. Floyd, E. Fiore, R.E. Gold, J.O. Goldsten, R.L. McNutt, Jr., and S.H. Bailey, Journal of Geophysical Research 102, 23729, 1997. reference.TROMBKAETAL1997B Veverka, J., J.F. Bell III, P. Thomas, A. Harch, S.L. Murchie, S.E. Hawkins III, J. Warren, E.H. Darlington, K. Peacock, C. Chapman, L. McFadden, M. Malin, and M. Robinson, An Overview Of The Near Multispectral Imager - Near-infrared Spectrometer Investigation, J. Geophys. Res., Vol. 102, pp. 23709-23727, 1997. reference.VEVERKAETAL1997A Veverka, J., P. Thomas, A. Harch, B. Clark, J.F. Bell III, B. Carcich, J. Joseph, C. Chapman, W. Merline, M. Robinson, M. Malin, L. McFadden, S.L. Murchie, S.E. Hawkins III, R. Farquhar, N.R. Izenberg, and A. Cheng, Near's Flyby Of 253 Mathilde: Images of a C Asteroid, Science, Vol. 278, pp. 2109-2114, 1997. reference.VEVERKAETAL1997B unk reference.VEVERKAETAL1999 Veverka, J., P.C. Thomas, J.F. Bell III, M. Bell, B. Carcich, B. Clark, A. Harch, J. Joseph, P. Martin, M. Robinson, S. Murchie, N. Izenberg, E. Hawkins, J. Warren, R. Farquhar, A. Cheng, D. Dunham, C. Chapman, W.J. Merline, L. McFadden, D. Wellnitz, M. Malin, W.M. Owen Jr., J.K. Miller, B.G. Williams, and D.K. Yeomans, Imaging Of Asteroid 433 Eros During Near's Flyby Reconnaissance, Science, Vol. 285, pp. 562-564, 1999. reference.VEVERKAETAL1999A Warren, J., K. Peacock, E.H. Darlington, S.L. Murchie, S. Oden, J. Hayes, J.F. Bell III, S. Krein, and A. Mastandrea, Near-infrared spectrometer for the Near Earth Asteroid Rendezvous mission, Space Science Review, Vol. 82, pp. 101-167, 1997. reference.WARRENETAL1997 Yeomans, D., A.S. Konopliv, and J.-P. Barriot, The NEAR Radio Science Investigations, Journal of Geophysical Research, 102(E10), 23775, 1997. reference.YEOMANSETAL1997 Yeomans, D.K., P.G. Antreasian, A. Cheng, D.W. Dunham, R.W. Farquhar, R.W. Gaskell, J.D. Giorgini, C.E. Helfrich, A.S. Konopliv, J.V. McAdams, J.K. Miller, W.M. Owen, Jr., P.C. Thomas, J. Veverka, and B.G. Williams, Estimating the mass of asteroid 433 Eros during the NEAR spacecraft flyby, Science, 285, pp. 560-561, 1999. reference.YEOMANSETAL1999 Zuber, M., D.E. Smith, A.F. Cheng, and T.D. Cole, The NEAR Laser Ranging Investigation, Journal of Geophysical Research, Vol. 102, pp. 23761-23773, 1997. reference.ZUBERETAL1997 NEAR INFRARED SPECTROMETER Spectrometer not applicable not applicable Instrument Overview =================== Launched on February 17, 1996, the Near Earth Asteroid Rendezvous (NEAR) spacecraft will go into orbit around the asteroid 433 Eros on February 14, 2000. The first launch of the Discovery class missions, NEAR will study this S-class asteroid up close, determining its geological characteristics, physical properties and composition [CHENG1997]. The reflected-light spectral data gathered by the Near Infrared Spectrometer (NIS) is a key component of an integrated strategy for the study of Eros. This strategy also includes high resolution imaging from the multispectral imager (MSI) [VEVERKAETAL1997A], elemental abundance measurements from the X-ray/gamma-ray spectrometer (XGRS) [TROMBKAETAL1997B], magnetic field data from the magnetometer (MAG) [ACUNAETAL1997], topographic data from the NEAR laser rangefinder (NLR) [ZUBERETAL1997], and mass and gravity data from the on-board radio science experiment [YEOMANSETAL1997]. NIS will conduct spectral mapping of Eros by measuring reflected sunlight in the wavelength range from 800 to 2600 nm. Reflectance spectra of Eros will be used to identify the surface mineral assemblages, to constrain the origin and evolution of the surface, and, in combination with other NEAR data, to explore the links between asteroids and meteorites. NEAR has traveled a circuitous path on its way to its orbital encounter with Eros [FARQUHARETAL1995], including a swing through the inner main asteroid belt that allowed a flyby of the C-type asteroid 253 Mathilde, a gravity-assist swingby of Earth, and an unplanned initial flyby of Eros itself following an aborted orbit-insertion burn [YEOMANSETAL1999], [VEVERKAETAL1999]. Due to inadequate power margins at the relatively large heliocentric distance during the target-of-opportunity encounter with Mathilde on June 27, 1997, NIS was not turned on at that time [VEVERKAETAL1997B]. The NIS instrument's protective cover was not opened until later in 1997, allowing observations of the on-board calibration target (caltarget) and of the Earth and Moon during the January 23, 1998 swingby maneuver. NIS first observed Eros in late December 1998 [VEVERKAETAL1999A]. Data from the Eros flyby provided a valuable opportunity to evaluate instrument performance. Observations of Eros will resume on final approach in early 2000 and continue throughout the mission as the orbit is changed in steps from 500 to 35 km radius. NIS was designed to fulfill four key NEAR measurement requirements [VEVERKAETAL1997A]: 1) Map the mineralogical composition of Eros using reflected sunlight 1) Map the distribution and abundance of minerals at scales as small as 300 meters 1) Complement high resolution MSI images and low resolution XGRS elemental distribution maps for definitive identification of rock types composing Eros' surface 1) Provide information on the physical and textural properties of these surface materials In order to fulfill these requirements, the instrument's behavior must be characterized both from rigorous preflight calibration and testing and from in-flight observations over the mission lifetime. This paper reviews the data and techniques used to calibrate the NIS, and discusses initial in-flight results for observations by NIS during the cruise, Earth swingby, and Eros flyby phases of the NEAR mission. The calibration of the instrument will be refined throughout the mission. Table two in the NIS calibration paper contains the science rationale for the phases and can be found in the NIS/DOCUMENT/INSTRUMENT/CALPAPER directory. Instrument Description ======================== NIS is composed of a grating infrared spectrometer, a scan mirror, two passively cooled detector modules, a mounting bracket, spectrometer electronics, and a data processing unit (DPU) that controls both the NIS and the NEAR magnetometer. NIS has a one-time deployable opaque cover, which was opened on September 24, 1997, three months after the Mathilde flyby [VEVERKAETAL1997B]. Hardware -------- The NIS design (Fig. 1) is copied from an earlier Applied Physics Laboratory (APL) spectrometer - the Defense Meteorological Satellite Special Sensor Ultraviolet Spectrographic Imager (SSUSI) - and modified for an infrared wavelength range. [WARRENETAL1997] detail the design characteristics, engineering, and construction of the instrument. A gold-coated scan mirror controls the direction of viewing over a range of 140 degrees. Light reflected from the scan mirror passes through a 20 x 25-mm aperture stop and is imaged by a telescope mirror at a slit. The field of view is selectable at the slit to 'narrow' (0.38 degrees x 0.76 degrees) or 'wide' (0.76 degrees x 0.76 degrees) settings. A shutter actuates the narrow slit, with the smaller slit opening coming down over the fixed wide slit. The two slits provide field-of-view sizes of 0.65 x 1.3 km or 1.3 x 1.3 km from 100 km distance. A second shutter can be actuated to completely block the slit for dark current measurements. After passing through the slit, light is dispersed and re- imaged off a gold toroidal diffraction grating (a Rowland circle configuration spectrometer) and hits a dichroic beamsplitter mounted at 45 degrees to the beam which transmits or reflects the energy to fall on two 32- element linear detector arrays. Reflected 2nd order wavelengths (804-1506 nm) fall on a germanium (Ge) array. Each Ge channel has a bandwidth of 21.6 nm. The germanium detector has a selectable gain of 1x or 10x. Transmitted 1st order wavelengths (1348-2732 nm) go to an indium-gallium-arsenide (InGaAs) array with 43.1 nm channel bandwidth. [WARRENETAL1997] calibrated the central wavelengths of all NIS channels at three operational temperatures (-7 degrees C, -17 degrees C, and -23 degrees C) and found best-fit Ge spectral calibration given by: lambda (nm) = 794.6 + 21.61*n (Equation 1) where n is Ge element number 1-32. The uncertainty of the wavelength calibration over the range of temperatures examined is +/-0.5 nm. InGaAs element center wavelengths are given by: lambda (nm) = 43.11*n - 50.8 (Equation 2) where n is InGaAs element number 33-64. The temperature-dependent wavelength uncertainty is approximately +/-3.5 nm. The lower two channels of the InGaAs detector (channels 33 and 34, at 1372 and 1315 nm respectively) are below the transition wavelength of the dichroic beamsplitter, and therefore always register very low signal. The upper 3 channels (channels 62-64 at 2622, 2665, and 2708 nm) are near or in detector cutoff, making the effective upper bound for good signal-to-noise ratio (SNR) around 2500 nm for the signal level expected at Eros. Additionally, two InGaAs channels (47 and 57, at 1975 nm and 2406 nm) have been extremely noisy since manufacture and do not produce easily usable data. Default operations for NIS utilize the narrow slit, providing a critically sampled spectral resolution of 22 nm in the Ge detector, and 44 nm in the InGaAs detector. The wide slit configuration provides half the spectral resolution (44 nm and 88 nm respectively), but passes twice the light and therefore has a higher SNR. The NIS scan mirror can rotate the line of sight over 350 steps in 0.4-degree increments in the spacecraft Z-X' plane. The +Z axis is perpendicular to the plane of NEAR's solar panels, and +X' is the boresight of the instruments. Mirror position 0 (nominal caltarget observation geometry) is 30 degrees towards the Z-axis from the boresight. The boresight is aligned with mirror position 75. Position 300 points in the -Z (anti-Sun) direction. For optimum performance the detectors are operated near -35 degrees C, maintained by passive cooling or active heaters, depending on the thermal environment. A solar-illuminated gold calibration plaque (caltarget) is mounted to the instrument for radiometric stability calibration. Table I summarizes the NIS specifications. More detailed descriptions of the NIS instrument design are presented in [PEACOCK1997] and [WARRENETAL1997]. Flight Software --------------- In-flight NIS data are acquired through the use of command sequences to the instrument that specify ten instrument parameters [NISAPLSRS1995], [IZENBERGETAL1998] as follows: 1. Spectrometer sequence ID (0-15). Sixteen sequences can be uploaded and stored while the instrument is powered. Sequences 0, 1, and 2 are hard-coded, but can be redefined. 2. Repeats: the number of times the commanded observations will repeat. 3. Seconds between repeats. 4. Number of observations. This is the number taken during a single repeat of the sequence. 5. Calibration interval (1-65535). Number of observations before acquisition of dark spectra. This is used to interleave shutter-closed dark observations with data observations. 6. Number of seconds to co-add spectral data in each observation (0-63). 7. Number of rest spectra (0-63). Used when interleaved darks are taken, between spectra acquisition and dark acquisition. 8. Number of co-added seconds of dark signal for interleaved dark spectrum. 9. Number of scan mirror steps between observations (sign indicates direction). 10. Seconds between observations. For the purposes of the software discussion, a 'spectrum' is the result of a one-second integration of the instrument as it gathers data. An 'observation' is 0-63 consecutive one-second spectra summed together. The example sequence ( 15 3 5 10 5 16 2 4 2 2 ) is interpreted as follows: Sequence ID is 15. The sequence will repeat three times, each iteration to contain 10 observations consisting of 16 co-added spectra of accumulated data. The calibration interval of five means that every 5th observation (numbers 5 and 10 in each repeat) will instead co-add 10 spectra of the target, then rest 2 seconds while the shutter closes, then take four co-added spectra of dark signal. After each accumulated observation, the scan mirror will move +2 steps and the instrument will rest two seconds. During each repeat, the mirror will move 20 steps. Each repeat is separated by five seconds to allow the mirror to return to the start position. This example sequence would generate 30 NIS observations of the target, and 6 dark observations. Choice of the wide or narrow NIS slit, the high or low Ge detector gain, and the starting NIS scan mirror position are specified through separate commands to the instrument.