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NIMS RADIANCE POINT SPECTRA OF GASPRA V1.0 (PDS)

NSSDCA ID: PSSB-00623

Availability: Archived at NSSDC, accessible from elsewhere

Description

This description was generated automatically using input from the Planetary Data System.

Data Set Overview

951 Gaspra radiance Near Infrared Mapping Spectrometer point spectra data description

1 - INTRODUCTION

This data volume contains a radiometrically corrected point spectra of asteroid 951 Gaspra as acquired by the Galileo spacecraft Near Infrared Mapping Spectrometer (NIMS, Carlson et al., 1992) on October 29, 1991 (Carlson et al., 1992B). These spectra record the observations of the NIMS sensor as the Galileo spacecraft approached the asteroid. These data are products of the calibration of the raw data number files gap015tn.qub, gap035tn.qub, gap036tn.qub, gap037tn.qub, and gap038tn.qub (DATA SET ID ='GO-A-NIMS-3-TUBE-V1.0') with calibration factors (DATA SET ID = 'GO-E-NIMS-4-MOSAIC-V1.0') acquired during the first Earth/Moon encounter of the Galileo mission. These raw data .qub files are archived in the Imaging Node of the NASA Planetary Data System (PDS). These calibrated spectra consist of radiance measurements for wavelengths between 0.7 - 5.2 micrometers. The data files are named by combining the name of the raw data source file and the data product type. For instance gap015radiance.tab is a combination of the first six characters of the source data file gap015tn.qub and the radiance data type. The .tab suffix indicates that the file is a PDS formatted text table file. The radiance data type refers to files that contain radiance spectra. The iof data type refers to files that with incidence over flux spectra.

2 - DATA OVERVIEW TABLE

File Bands Object Observation Target Start(UT) Distance(km) gap015radiance.tab 329 951 Gaspra 22:01:16 14820.1 gap015iof.tab 329 951 Gaspra 22:01:16 14820.1 gap035radiance.tab 17 951 Gaspra 21:38:18 26585.1 gap035iof.tab 17 951 Gaspra 21:38:18 26585.1 gap036radiance.tab 17 951 Gaspra 21:51:36 21024.7 gap036iof.tab 17 951 Gaspra 21:51:36 21024.7 gap037radiance.tab 100 951 Gaspra 21:54:29 17624.2 gap037iof.tab 100 951 Gaspra 21:54:29 17624.2 gap038radiance.tab 100 951 Gaspra 22:07:13 10391.9 gap038iof.tab 100 951 Gaspra 22:07:13 10391.9

3 - GALILEO MISSION DESCRIPTION

Galileo was a mission to Jupiter to perform long-term studies of the Jovian atmosphere and detailed studies of the Galilean satellites (Wolf, 1992). It consisted of a two part spacecraft, an orbiter and an atmospheric probe. Both components were launched from the space shuttle Atlantis on October 18, 1989. The orbiter contained remote sensing, particles, and wave sensors. The remote sensing instruments included the Solid State Imager and the Near Infrared Mapping Spectrometer. The atmospheric probe contained in-situ sensors to directly measure the atmosphere of Jupiter. The Galileo spacecraft encountered Venus (February 10, 1990), the Earth Moon system (December 8, 1990 and December 8, 1992), asteroid 951 Gaspra (October 29, 1991), asteroid 243 Ida (August 28, 1993) before entering the orbit of Jupiter on December 8, 1995. This data set is from the asteroid 243 Ida encounter. The Galileo mission investigated the Jovian system by deploying its atmospheric probe on July 13, 1995 and conducting observations until plunged into Jupiter on September 21, 2003.

4 - INSTRUMENT DESCRIPTION

The Near Infrared Mapping Spectrometer (Carlson et al., 1992) instrument was an imaging spectrometer covering the wavelength region 0.7 to 5.2 micrometers. Its spectral resolution is 0.025 micron beyond 1 micron, and 0.0125 microns below 1 micron, yielding 204 spectral elements in nominal mode. The nominal pixel size is a square 0.5 x 0.5 milliradians. The instrument acquires data in the order: (1) sampling of 17 detectors, (2) stepping of the scan mirror (20 elements in cross-cone), (3) stepping of the grating (nominally 12 steps per cycle). The nominal 204 wavelength cycle requires 4 1/3 seconds. The detectors (2 silicon, 15 indium antimonide) sample approximately uniformly across the spectrum. The stepping of the grating provided NIMS with a variety of spectral data collection modes that ranged from 17 channels (no grating step movements) to 408 channels (24 grating step movements).

5 - 951 GASPRA ASTEROID ENCOUNTER NIMS OBS

The Galileo spacecraft performed a flyby encounter of asteroid 951 Gaspra with its closest approach occurring at 22:37:00 on October 29, 1991 UTC. The closest approach was at 951 Gaspra's dark side, 3.9 degrees north ecliptic latitude, at a 1600 kilometer range. NIMS conducted four types of science observations during the 951 Gaspra encounter. The highest priority observation was two scans of the asteroid in fixed map mode (17 spectral channels) at a time near the closest approach. The goal was to collect spatially resolved spectral data of 951 Gaspra. The second priority observation time was to collect short map mode (102 spectral channels) at broken intervals with low phase angles. The goal of these observations was to acquire the best spectral observations during the 951 Gaspra encounter. The third priority observation type was to collect full map mode (408 spectral channels) during every 90 degrees of asteroid rotation. This was to provide the highest spectral sampling of the asteroid as it rotated. The lowest priority observations for NIMS was to collect short map mode data every 30 degrees and fixed map mode data at every 15 degrees of asteroid rotation. Thirty two observations of all of these types were conducted by the NIMS sensor during this encounter. Radiometric and photometric calibration observations were conducted by NIMS after the completion of the science observation sequence. The products in this data volume are a subset of the NIMS observations of asteroid 951 Gaspra. They do not include the closest approach fix map mode data. That data has been calibrated and archived as the GO-A-NIMS-4-GASPRACUBE-V1.0 in the PDS Small Bodies Node. They do include five files containing two fixed map, two short map, and a full map mode observation that occurred just prior to the closest approach observations. Thirty seven files are archived the NIMS observations of 951 Gaspra in the PDS Imaging Node. The data set was reduced to five observations by calibrating only the data that had significant target signal and that did not include the closest approach data.

6 - DATA FILE FORMAT DESCRIPTION

The data files for the 951 Gaspra radiance Near Infrared Mapping Spectrometer point spectra are ASCII (American Standard Code for Information Interchange) text files. Each data file contains columns of floating point numeric values separated by spaces. The radiance files consist of columns of wavelength values (micrometers), radiance (microwatts*centimeters**-2*steradians** -1*micrometers**-1), and instrument radiance precision (microwatts*centimeters**-2*steradians** -1*micrometers**-1). The calibration files consist of columns of wavelength values (micrometers), sensitivity (micrometers*steradians*centimeters**2*microwatts**-1), and dark values (data number). The sol (short for solar) files consist of columns of wavelength values (micrometers) and radiance (microwatts*centimeters**-2*steradians** -1*micrometers**-1). The iof files consist of columns of wavelength values (micrometers), incidence over flux ratio values, and instrument incidence over flux ratio precision values.

7 - DATA PROCESSING HISTORY

The radiance data in this data volume are derived from archived NIMS spectral images files available from the NASA PDS Imaging Node. The 951 Gaspra NIMS observations are archived in the Imaging Node as spectral image files of data number or instrument count values (DATA SET ID ='GO-A-NIMS-3-TUBE-V1.0'). These data number values were converted into radiance using the following equation: radiance value = (data number value - dark value)/sensitivity value. The dark value was determined through an average of background sky pixels for the observation. The sensitivity value was obtained from recorded values used to process the NIMS observations of the Earth and Moon (DATA SET ID = 'GO-E-NIMS-4-MOSAIC-V1.0') that employed the same instrument collection modes and gains as the 951 Gaspra observations. Full map and short map mode data were subjected to a running box filter average to compensate for spacecraft/scan platform motion (jitter) while the NIMS sensor cycled through multiple grating positions. This small (jitter) motion causes unresolved observations to have small variations in their optical path through the sensor as a multiple grating step spectrum is being collected. If the motion is of sufficient scale, it can impart a periodic variation in radiance in wavelength space. The box filter sample size was determined when a repetition of saw teeth like radiance values were no longer present in the spectral data. The solar radiance spectra were modeled from NIMS solar radiance spectra archived in observations of the Earth and Moon DATA SET ID = 'GO-E-NIMS-4-MOSAIC-V1.0') and the 951 Gaspra, Galileo spacecraft, and Sun geometry data stored in the Galileo mission SPICE kernels. The inverse square law was used to scale the values from the Earth/Moon observation data set to the appropriate values for the 951 Gaspra observations. The incidence over flux spectra were created by ratioing the radiance spectra with the modeled solar radiance spectra. File specific processing information can be found in the following paragraphs of this section. The file gap015radiance.tab is derived from DN values from line 9 sample 11 in PDS file GAP015TN.QUB (DATA SET ID GO-A-NIMS-3-TUBE-V1.0) and calibrated with values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-E-NIMS-4-MOSAIC-V1.0). Radiance data was subjected to a running box average filter of 21 samples. Channels with no signal are not included in this data file. The file gap015calibration.tab contains the calibration values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-E-NIMS-4-MOSAIC-V1.0) used to create gap015radiance.tab. The calibration coefficients include the sensitivity offset calculated by the running box average filter. The gap015sol.tab contains the modeled radiance solar spectrum that illuminated asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 22:01:16 UT on October 29, 1991. It was modeled using solar radiance data archived in the NASA PDS Imaging Node file E1WANTA2CI.QUB from the GO-E-NIMS-4-MOSAIC-V1.0 data set. The gap015iof.tab contains the incidence over flux spectrum of asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 22:01:16 UT on October 29, 1991. It was created by a ratio of gap015radiance.tab by gap015sol.tab with a 50% pixel fill factor. The file gap035radiance.tab is derived from DN values from line 69 sample 4 in PDS file GAP035TN.QUB(DATA SET ID =GO-A-NIMS-3-TUBE-V1.0) and calibrated with values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-E-NIMS-4-MOSAIC-V1.0). The file gap035calibration.tab contains the calibration values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-E-NIMS-4-MOSAIC-V1.0) used to create gap035radiance.tab. The gap035sol.tab contains the modeled radiance solar spectrum that illuminated asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 21:38:18 UT on October 29, 1991. It was modeled using solar radiance data archived in the NASA PDS Imaging Node file E1WANTA2CI.QUB from the GO-E-NIMS-4-MOSAIC-V1.0 data set. The gap035iof.tab contains the incidence over flux spectrum of asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 21:38:18 UT on October 29, 1991. It was created by a ratio of gap035radiance.tab by gap035sol.tab with a 33% pixel fill factor. The file gap036radiance.tab is derived from DN values from line 252 sample 18 in PDS file GAP036TN.QUB (DATA SET ID GO-A-NIMS-3-TUBE-V1.0) and calibrated with values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-E-NIMS-4-MOSAIC-V1.0). The file gap036calibration.tab contains the calibration values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-J-NIMS-4-MOSAIC-V1.0) used to create gap036radiance.tab. The gap036sol.tab contains the modeled radiance solar spectrum that illuminated asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 21:51:36 UT on October 29, 1991. It was modeled using solar radiance data archived in the NASA PDS Imaging Node file E1WANTA2CI.QUB from the GO-E-NIMS-4-MOSAIC-V1.0 data set. The gap036iof.tab contains the incidence over flux spectrum of asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 21:51:26 UT on October 29, 1991. It was created by a ratio of gap036radiance.tab by gap036sol.tab with a 33% pixel fill factor. The file gap037radiance.tab is derived from DN values from line 34 sample 18 in PDS file GAP037TN.QUB (DATA SET ID GO-A-NIMS-3-TUBE-V1.0) and calibrated with values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-E-NIMS-4-MOSAIC-V1.0). Radiance data was subjected to a running box average filter of 9 samples. The file gap037calibration.tab contains the calibration values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-E-NIMS-4-MOSAIC-V1.0) used to create gap037radiance.tab. The calibration coefficients include the sensitivity offset calculated by the running box average filter. The gap037sol.tab contains the modeled radiance solar spectrum that illuminated asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 21:54:29 UT on October 29, 1991. It was modeled using solar radiance data archived in the NASA PDS Imaging Node file E1WANTA2CI.QUB from the GO-E-NIMS-4-MOSAIC-V1.0 data set. The gap037iof.tab contains the incidence over flux spectrum of asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 21:54:29 UT on October 29, 1991. It was created by a ratio of gap037radiance.tab by gap037sol.tab with a 33% pixel fill factor. The file gap038radiance.tab is derived from DN values from line 49 sample 17 in PDS file GAP038TN.QUB (DATA SET ID GO-A-NIMS-3-TUBE-V1.0) and calibrated with values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-E-NIMS-4-MOSAIC-V1.0). Radiance data was subjected to a running box average filter of 7 samples. The file gap038calibration.tab contains the calibration values from the PDS file E1WANTA2CI.QUB (DATA SET ID GO-E-NIMS-4-MOSAIC-V1.0) used to create gap038radiance.tab. The calibration coefficients include the sensitivity offset calculated by the running box average filter. The gap038sol.tab contains the modeled radiance solar spectrum that illuminated asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 22:07:13 UT on October 29, 1991. It was modeled using solar radiance data archived in the NASA PDS Imaging Node file E1WANTA2CI.QUB from the GO-E-NIMS-4-MOSAIC-V1.0 data set. The gap038iof.tab contains the incidence over flux spectrum of asteroid 951 Gaspra as observed by the Galileo spacecraft Near Infrared Mapping Spectrometer at 22:01:13 UT on October 29, 1991. It was created by a ratio of gap038radiance.tab by gap038sol.tab with a 66% pixel fill factor.

8 - POINT SPECTRA SUPPORT INFORMATION

The point spectra support data information can be found in the table file science_index.tab. This information includes the name of the data file, the name of the source file archived in the Imaging Node of the PDS, the instrument spacecraft mission name, the instrument name, the spacecraft mission phase name, the target of the observation, the instrument observation type/mode, the observation identifier, the observation start and stop time (Universal Time), the observation start and stop time in Julian date, the observation start and stop time as recorded by the spacecraft clock, the instrument to target center distance (kilometers), the target to Sun distance (kilometers), the spacecraft to Sun position vector in the J2000 reference frame (kilometers), the target to Sun position vector in the J2000 reference frame (kilometers), the target to Earth distance (kilometers), the spacecraft to Earth position vector in the J2000 reference frame (kilometers), the Earth to target position vector in the J2000 reference frame (kilometers), the horizontal pixel scale (kilometers), the vertical pixel scale (kilometers), the observation phase angle (degrees), the Earth to spacecraft state vector in the J2000 reference frame (position in kilometers, velocity in kilometers/second), and the Earth to target state vector in the J2000 reference frame (position in kilometers, velocity in kilometers/second). These geometry values were calculated using the SPICE Tool kit and the following SPICE data files: s970311a.bsp, naif0008.tls, mips010314.tpc, and mk00062a.tsc. 9 -

9 - REFERENCES

Carlson, R. W., P. R. Weissman, W. D. Smythe, J. C. Mahoney, NIMS-Science-Team, and NIMS-Engineering-Team (1992), Near-Infrared Mapping Spectrometer Experiment on Galileo, Space Science Reviews, 60, 457-502. Carlson, R. W., P. R. P.R. Weissman, W. D. Smythe, L. C. Byrne, A. C. Ocampo, L. A. Soderblom, H. H. Kieffer, F. Fanale, J. Granahan, and T. B. McCord (1992B), Gaspra: Spatially resolved infrared spectra from Galileo, Bulletin of the American Astronomical Society, 24, 932. Wolf, A. A. (1992), Jet Propulsion Laboratory Interoffice Memorandum GLL-NAV-92-90, Satellite Tour 92-14A Data Package, May 12, 1992.

These data are available on-line from the Planetary Data System (PDS) at:

http://sbn.psi.edu/pds/asteroid/GO_A_NIMS_3_GASPRASPEC_V1_0/

Alternate Names

  • GO-A-NIMS-3-GASPRASPEC-V1.0

Discipline

  • Planetary Science: Small Bodies

Additional Information

Spacecraft

Experiments

Questions and comments about this data collection can be directed to: Dr. Edwin V. Bell, II

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Robert W. CarlsonData ProviderNASA Jet Propulsion Laboratoryrcarlson@issac.jpl.nasa.gov
Mr. James C. GranahanGeneral ContactUniversity of Hawaiigranahan@uhpgvax.pgd.hawaii.edu
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