Description of the the Hi-Res Galileo NIMS Gaspra Spectral Image Cube bundle V1.0 ================================================================================= Note: This bundle was migrated to PDS4 from the PDS3 data set GO-A-NIMS-4-GASPRACUBE-V1.0. For PDS3 data sets migrated to PDS4, the following text is taken from the data set descriptions and other documents which have been consolidated and updated into this PDS4 bundle_description. Data Set Overview ================= This bundle contains a radiometrically calibrated and spatially rectified spectral image cube of the highest spatial resolution observation of asteroid 951 Gaspra as acquired by the Galileo spacescraft Near Infrared Mapping Spectrometer (NIMS) on October 29, 1991. It was generated by Science Application International Corporation for the contract NNH10DC54C for the NASA Planetary Mission Data Analysis Program. It is the product of the calibration of the raw data number file gap016tn.qub with calibration factors contained in the file e1wanta2.qub and projected in a point perspective geometry. Both files are contained within the NASA pds archive of Galileo NIMS data. This spectral image cube, gaspra_nims_hires_radiance.fit, combines data acquired during the asteroid 951 Gaspra encounter and the Earth encounters to produce a radiometrically calibrated product. The Near-Infrared Mapping Spectrometer (NIMS) instrument is an imaging spectrometer covering the wavelength region 0.7 to 5.2 micrometers measuring both reflected sunlight and emitted thermal radiation in a region incompletely studied by the Pioneer and Voyager spacecraft. Its spectral resolution is 0.025 micron beyond 1 micron, and 0.0125 microns below 1 micron, yielding 204 spectral elements in nominal mode. (It could produce spectra over as many as 408 wavelengths). 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 Antinomide) sample approximately uniformly across the spectrum. A detailed description of the instrument may be found in [CARLSONETAL1992] and in the document directory of this bundle. The natural form of imaging spectrometer data is the spectral image cube. It is normally in band sequential format, but has a dual nature. It is a series of 'images' of the target, each in a different wavelength. It is also a set of spectra, each at a particular line and sample, over the area observed. Each spectrum describes a small portion of the area. When transformed into cubes, the data may be analyzed spatially, an image at a time, or spectrally, a spectrum at a time, or in more complex spatial-spectral fashion. The gaspra_nims_hires_radiance data product is a spectral image cube of the highest spatial resolution NIMS observations of asteroid 951 Gaspra. It is derived from data archived in the NASA Planetary Data Systems file gap016tn.qub that consists of data in raw data number values stored as a spectral image cube in a band sequential integer array. These raw data numbers were converted into little endian floating point values using sensor sensitivity values contained in the NIMS Earth observation e1wanta2.qub also archived in the NASA Planetary Data System. The gaspra_nims_hires_radiance pixels were rectified by creating a point perspective instrument projection and limbfitting pixels to the corresponding 951 Gaspra Galileo spacecraft CCD (Solid State Imager). The result is a rectified band sequential radiance spectral image cube of 951 Gaspra that is stored in the gaspra_nims_hires_radiance FITS file. Parameters ========== A band in a NIMS tube is generated for each of the 17 detectors at each grating step. (The detectors cover the range 0.7 to 5.2 microns.) The motion of the grating is determined by the commanded instrument mode: Mode Grating Grating Bands Samples/RIM steps increment Fixed Map/Spectrometer 1 0 17 182 Short Map/Spectrometer 6 4 102 26 Full Map/Spectrometer 12 2 204 14 Long Map/Spectrometer 24 1 408 7 A secondary mirror moves through twenty cross-track positions in the map modes, or is fixed near the center of its scan in the spectrometer modes. The number of lines in each image of a tube is always twenty, whether or not the mirror is moving. The number of samples is determined by the mode and the duration of the observation. (In the mosaic dataset, the image dimensions are determined by the pattern created by the motions of the secondary mirror and the scan platform.) The approximate wavelengths of the bands are determined by the mode, and by offset and start grating positions. The true wavelengths are functions of the temperature of the grating and parameters determined from the ground calibration and frequent optical flight calibrations. Known absorptions on some targets are also useful in determining these parameters. The commanded gain state is one of four sets of gains for the 14 non-thermal detectors. The three thermal detectors have two gains, automatically switching to the lower one near the mid-point of their range. Raw data values of each detector and grating step are functions of the gain state and the temperature of the focal plane assembly (FPA). Radiances are determined from raw data values using sensitivities based on the original ground calibration corrected by frequent photometric and radiometric flight calibrations. I/F values are simply radiances divided by the solar absorption at the target's distance from the sun for the wavelength in question. Further details may be found in volinfo.txt in the document directory of the archive volume, and in the instrument paper instpub.txt [CARLSONETAL1992]. Processing ========== The gaspra_nims_hires_radiance data product is a spectral image cube of the highest spatial resolution NIMS observations of asteroid 951 Gaspra. It is derived from data archived in the NASA Planetary Data Systems file gap016tn.qub that consists of data in raw data number values stored as a spectral image cube in a band sequential integer array. These raw data numbers were converted into little endian floating point values using sensor sensitivity values contained in the NIMS Earth observation e1wanta2.qub also archived in the NASA Planetary Data System. These values were selected from the 1990 Galileo NIMS observation of Antarctica due to the fact that it was near the October 29, 1991 asteroid 951 Gaspra observations in time and that it produced values that agreed with the spectral image measurements of the same target with the Galileo Solid State Imager experiment. Values from other phases of the Galileo mission were tested (Earth Moon 2 encounter and the Jupiter Tour) and did not agree with values from the Solid State Imager experiment, ground based Eight Color Asteroid Survey data, or NASA Infrared Telescope Facility data. This is most likely due to changes in the Galileo NIMS silicon detectors (1 and 2) that transpired later in the mission. The gaspra_nims_hires_radiance pixels were rectified by creating a point perspective instrument projection and limbfitting pixels to the corresponding 951 Gaspra Galileo spacecraft CCD (Solid State Imager). The result is a rectified band sequential radiance spectral image cube of 951 Gaspra that is stored in the gaspra_nims_hires_radiance FITS file. Geometry Notes ============== The primary file geometry for the gaspra_nims_hires_radiance data product was calculated through the use of the NAIF Toolkit IDL tools. The projection of the NIMS pixel values was checked via a limbfit to the Galileo Solid State Imager highest resolution images acquired during the NIMS observation sequence that collected the data for the gaspra_nims_hires_radiance data product. Geometry files are not included in this bundle. The geometry calculated for the included data product were derived from the following SPICE files available from NAIF (http://naif.jpl.nasa.gov) using the NAIF toolkit: s970311a.bsp - spk file naif0008.tls - lsk file mips010314.tpc - pck file mk00062a.tsc - sdk file Kay Edwards' map of Galileo boom obscurations as a function of scan platform cone and clock angles is used to remove boom interference from NIMS products. Data structure ============== The gaspra_nims_hires_radiance.fit file is a FITS formatted file that contains three little endian floating point arrays with associated header data. The first array is a three dimensional that is a radiance spectral image cube of the asteroid 951 Gaspra in a band sequential format. The second array is another three dimensional array that contains the per pixel wavelength value of the pixels in the first array. The third array is a three dimensional array that contains the radiance precision of each pixel of the radiance spectral image cube. This FITS file has a detached PDS label file that describes the FITS data file structure, spacecraft mission, and the observation geometry. Directory Structure and Content =============================== Every file in the bundle has an accompanying .xml label (not explicitly mentioned below) top directory ------------- Bundle Information: bundle_galileo.ast-gaspra.nims.spectral-cubes.xml data directory -------------- Collection inventory: collection_galileo.ast-gaspra.nims.spectral-cube_data_inventory.csv Galileo NIMS spectral cube for Gaspra: gaspra_nims_hires_radiance.fit Calibration file with sensitivity and dark values: calib.tab browse directory ---------------- Collection inventory: collection_galileo.ast-gaspra.nims.spectral-cube_browse_inventory.csv Browse content information: browse_info.txt Radiance image for band 1: gaspra_nims_hires_radiance_band_1.tif Sample spectra: gaspra_nims_hires_radiance_sample_spectra.tif document directory ------------------ Collection inventory: collection_galileo.ast-gaspra.nims.spectral-cube_document_inventory.csv Document content information: AA_Document_Index.txt Detailed bundle description: bundle_description.txt NIMS instrument overview: nimsinst.txt NIMS instrument document in ASCII: instpub.txt Accompanying graphic figures for instpub.txt: instfg.pdf NIMS guide to the Gaspra encounter in ASCII: nimsgd.txt Accompanying graphic figures for nimsgd.txt: nimsgd.pdf References: ref.txt Ancillary Data ============== Guides (in text and pdf files) to the planned observations, including footprint plots on the target, instrument parameters, etc. are included in the data set, as are tables of parameters for each observation. A copy of the NIMS instrument paper instpub.txt [CARLSONETAL1992] is also included in text and accompanying figures in pdf formats. The calibration factors and dark current values used to create the radiance spectral image cube are included in the data directory as an ASCII formatted table file. These values were obtained from the E1WANTA2.QUB NIMS Earth observation that is archived in the NASA PDS Imaging node. Tagged Image File Format (TIFF) files containing sample images of the data in the gaspra_nims_hires_radiance can be found in the browse directory. Software ======== NIMS tubes were designed to be accessed by the ISIS system. No software is provided with the gaspra_nims_hires_radiance data volume. The FITS formatted file can be read with astronomical image software packages that can ingest the FITS file format. This includes IDL, a product of ITTVIS (http://www.ittvis.com) with the IDL Astronomy User's Library at NASA Goddard Space Flight Center at http://idlastro.gsfc.nasa.gov . ISIS (Integrated Software for Imagers and Spectrometers) 3.0 may also be used to ingest the FITS file for analysis and is available from the USGS via http://isis.astrogeology.usgs.gov/. Confidence Level Overview ========================= The radiance values contained in the gaspra_nims_hires_radiance data set were checked against corresponding values obtained by the Galileo Solid State Imager (SSI) multi-spectral imagery, NASA Infrared Telescope Facility spectra, and Eight Color Asteroid Survey data for asteroid 951 Gaspra. This permitted the selection of the best calibration factors that represented the NIMS instrument at the time of the 951 Gaspra. The shape of the limb of asteroid 951 Gaspra as observed by SSI was also used as a constraint for the position of the NIMS pixels in the data set. Each NIMS scan line was aligned into the SSI imaged asteroid limb during the time of the observation. The updated alignment was used to position the NIMS pixels in the gaspra_nims_hires_radiance data product. Data Coverage and Quality ========================= The gaspra_nims_hires_radiance data product contains only the highest spatial resolution NIMS observations of asteroid 951 Gaspra. It contains data from the NIMS observation that is of a high signal to noise. Lower signal to noise scans (near limb) of the asteroid were omitted from this data set. Galileo Mission Overview ======================== Galileo was a mission to Jupiter to perform long-term studies of the Jovian atmosphere and detailed studies of the Galilean satellites. The mission is divided into a launch/cruise phase and an orbital phase. The spacecraft trajectory required a deltaV Venus-Earth-Earth gravity assist (VEEGA). The cruise is divided into Earth-Venus (EV), Venus-Earth (VE), Earth-Earth (EE) and Earth-Jupiter segments -- with the initials used to associate observations with time. These cruise segments are further divided by spacecraft command loads, which are numbered, but not completely contiguously since some planned loads were later combined or eliminated. Important segments include VE6 (Venus encounter), EV9 and 11 (Earth 1 encounter), EE3 (Gaspra encounter), EE9 and 11 (Earth 2 encounter), EJ2 and EJ3 (Ida encounter) and EJ7 (Shoemaker-Levy 9 impact with Jupiter). Jupiter operations are divided into encounters, named for the satellite which is the principal target. The primary missions consist of the Jupiter Orbit Insertion (JOI) phase and Io encounter (I0) followed by encounters with Ganymede (G), Callisto (C) and Europa (E) designated by principal target and orbit number: G1, G2, C3, E4, E6, G7, G8, C9, C10 and E11. Data is not collected during the fifth encounter (J5) because Jupiter is behind the sun. [The Galileo Europa Mission (GEM) follows the Primary Mission. It will continue data collection in the Jupiter system, though primarily data from Europa and Io. There will be eight close encounters of Europa (E12, E14, E15, E16, E17, E18 and E19), four of Callisto (C20, C21, C22 and C23) and two of Io (I24 and I25) over a period of two years. Jupiter is behind the sun during the 13th encounter (E13).] The spacecraft was a dual-spinner, with the fundamental coordinate system in EME-1950 (Right Ascension, Declination, and Twist) and a hardware coordinate system in cone and clock. The associated spacecraft geometry is available as SPICE kernels generated by the NAIF group at JPL. The fundamental unit of the spacecraft clock is the RIM (Realtime IMaging count, 60 2/3 seconds). This is subdivided into 91 minor frames (2/3 seconds each) numbered from 0 to 90. Each minor frame is in turn subdivided into 10 RTIs (RealTime Interrupts), numbered 0 to 9. The spacecraft clock time is usually represented in the notation RIM:MF:RTI, where MF denotes the minor frame. Planned spacecraft events are described in the SSDF (Standard Sequence Data File). It is the source of several other files, including the ORPLN (ORbit PLaNning) file, the SEF (Spacecraft Event File) and the ISOE (Integrated Sequence Of Events) file. These are available through the Galileo Science Catalog. Contributions by ================= James Granahan, Bob Mehlman, Frank Leader, Bob Carlson, Bill Smythe, Lucas Kamp, Ashley Davies, Valerie Henderson, Tyler Brown, Eric Eliason, Chris Isbell. Acknowledgments =============== The gaspra_nims_hires_radiance data product was created for the National Aeronautics and Space Administration Planetary Data System with support from contract NNH10CD54C with Science Application International Corporation through the Planetary Mission Data Analysis Program. Format guidance for the data product was provided by Carol Neese of the Planetary Science Institute. A special thanks also goes to NASA and the Galileo NIMS team (led by Dr. Robert Carlson of Jet Propulsion Laboratory) for flying the Galileo mission to asteroid 951 Gaspra, conducting the spectral observations, and archiving the data to the NASA PDS system. This work is also indebted to NASA Goddard Space Flight Center that maintains the Flexible Image Transportation System (FITS) file format and the IDL user's astronomical libary, the Navigation and Ancillary Information Facility (NAIF) at JPL, and the software team at the United States Geological Survey that maintains the Imaging Software for Imagers and Spectrometers (ISIS). All of these parties contributed in the creation of the gaspra_nims_hires_radiance data product.