PDS_VERSION_ID = PDS3 /* GO_1104: sl9ds.cat */ LABEL_REVISION_NOTE = " 1999 Aug 13 - Original by R Mehlman, UCLA/IGPP, based on material by R W Carlson, NIMS P.I., JPL" RECORD_TYPE = STREAM OBJECT = DATA_SET DATA_SET_ID = "GO-J-NIMS-4-ADR-SL9IMPACT-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = " GALILEO NIMS ANALYSIS OF SL-9 IMPACT WITH JUPITER" DATA_SET_COLLECTION_MEMBER_FLG = "Y" START_TIME = 1994-195T08:09:03Z STOP_TIME = 1994-202T05:14:48Z DATA_SET_RELEASE_DATE = 1995-11-19 DATA_OBJECT_TYPE = TABLE PRODUCER_FULL_NAME = "DR. ROBERT W. CARLSON" DETAILED_CATALOG_FLAG = "N" DATA_SET_DESC = " Data Set Overview ================= In July of 1994, the Galileo Near Infrared Mapping Spectrometer (NIMS) acquired unique data during the collision of Comet Shoemaker-Levy 9 (SL9) with Jupiter. The spacecraft, enroute to Jupiter, was situated 240 million kilometers from that planet with a spacecraft-Jupiter-Sun phase angle of 51 degrees. This geometry allowed a direct view of the impacts, which occurred on the nightside of Jupiter, not viewable from the Earth, and provided an opportunity to investigate the early temporal evolution of the impact events. Much of the radiation occurs in the infrared region, and time-resolved infrared spectral observations, obtained over a broad wavelength range, are ideal for studying these phenomena. The NIMS instrument [CARLSONETAL1992] observed the C, F, G, and R events, simultaneously with the Photopolarimeter (PPR) and Ultraviolet Spectrometer (UVS) instruments, but only data for the G and R events were returned to Earth. In order to ensure successful observations of the impacts, given uncertainties in the absolute spacecraft pointing, a 'checkerboard' scan pattern was used, covering Jupiter and the immediate vicinity. One dimension of scanning was provided by the NIMS mapping capability, giving a 10 mrad column of 20 pixels. Each pixel is acquired in 1/63 sec and is 0.5 mrad by 0.5 mrad in size. (Jupiter's diameter as seen from Galileo was 0.6 mrad). The spacecraft scan platform provided the second dimension, scanning back and forth by 3 mrad at 0.92 mrad/sec and a period of 10 2/3 sec. Jupiter was in the field-of-view for only a fraction of each scan, giving a net time resolution of 5 1/3 seconds. The instrument was operated in the 'Fixed Map' mode in which, for each spatial pixel, 17 spectral bands are simultaneously monitored. The wavelength setting was chosen to include continuum bands, where the atmospheric gases are transparent, and bands with differing absorption strengths so as to perform vertical sounding of the fireball in the atmosphere. It also included a band for possible H3+ emissions. For short wavelengths, the intense reflected sunlight signal precludes ready identification of fireball emission while Jovian thermal emission obscures the fireball signature in the 5 micron region Between these limits, in the 1.8 to 4.4 micron region, the reflected sunlight signal is weak and little atmospheric thermal emission occurs. Consequently, we employed this region for our preliminary analysis. The corresponding wavelengths and atmospheric absorption properties are listed in Table 1. The spectral resolution for each wavelength channel is 0.025 microns. --------------------------------------------------------------------- Table 1. Wavelengths and Jovian Atmospheric Absorption Properties Det. No. Wavelength Wavenumber Absorber, Emitter (microns) (cm-1) ======== ========== ========== ========================== 6 1.84 5430 Continuum 7 2.12 4710 Molecular hydrogen, pressure induced 8 2.40 4160 Methane (stratosphere) 9 2.69 3720 Continuum 10 2.97 3370 Ammonia (troposphere) 11 3.25 3075 Methane (stratosphere) 12 3.53 2830 '' '' , H3+ 13 3.82 2620 '' '' 14 4.10 2440 Continuum 15 4.38 2280 Phosphine (troposphere) -------------------------------------------------------------------- The data provided for the G and R events are of three types: calibration data, raw and averaged data numbers, and processed data, giving source intensities in physical units. The raw data are extracted from NIMS Experiment Data Records (EDRs), archived separately on the CD-ROM volume GO_1004. Preliminary results were published in [CARLSONETAL1995A] and [CARLSONETAL1995B]. A comprehensive paper on the G fireball was published in [CARLSONETAL1997], and an analysis of the G and R splash spectra is currently underway. Parameters ========== The NIMS instrument was operating in a very specific mode during the SL9 encounter, so a detailed description of its capabilities is not given here. The instrument was in 'Fixed Map' mode, in which 17 detectors are sampled while a secondary mirror moves through twenty cross-track positions. NIMS was in its highest gain state. The approximate wavelengths of the 17 bands are determined by the offset and start grating positions. The true wavelengths are functions of the temperature of the grating and parameters determined from the ground calibration and optical flight calibrations. Raw data values of each detector are functions of 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 photometric and radiometric flight calibrations. Processing ========== Jupiter, during the SL-9 impact, was only slightly more than a single NIMS pixel (.5 mrad) across. So in the EDRs, non-dark NIMS DNs (from Jupiter) are pretty much restricted to a 2x2 array of pixels in each of the 17 detectors, each time the secondary mirror scans cross the planet. (The spacecraft scan platform was moving back and forth, from side to side, across Jupiter's expected position.) Therefore the usual method of organizing NIMS data, as spectral image cubes generated from the time-ordered EDRs, was not applicable. Fragments G and R were observed for some time, but it was possible to return only about 20 of the 2x2 arrays, in each detector, per fragment. These data are buried in the EDRs for this period, which consist mostly of dark sky DNs. But they have been extracted from the EDRs and organized into two tables, one per fragment, of sets of 17 detector DNs -- containing at least one non-dark DN -- as functions of time. Additional tables contain calibration parameters and pre-impact reference spectra for Jupiter. Source intensities of the impact site versus time were computed by (1) dark-correcting and summing sensor values from the two successive mirror positions containing the signal and multiplying by the instrumental sensitivity, (2) similarly dark-correcting the weighted mean Jupiter reference spectrum and normalizing it to detector 1, (3) subtracting the appropriate fraction (eta) of the Jupiter reference from the sensed results, (4) correcting the results for cloud reflection and (5) putting them into source intensity units. Several methods were used to compute eta. (Details may be found in the table labels.) These tables comprise the 'science' derived from the NIMS data for the impact. The NIMS team believes the complete set of tables is the most useful NIMS product for the final SL9 archive. Data structure ============== This submission consists of nine (9) data tables, each accompanied by a detached PDS label. The tables are in PDS ASCII format, with extension .TAB. The corresponding labels have the same names, with extension .LBL, and describe the individual columns. The tables are: CAL_DATA.TAB: A file of calibration data and related information useful for interpretation. JREF_DNS.TAB: Reference spectra for the undisturbed full disc Jupiter, in data numbers (DNs). JREF_GAM.TAB: Reference spectra for Jupiter's morning hemisphere, just prior to the G fireball event, in DNs. JREF_RAM.TAB: Reference spectra for Jupiter's morning hemisphere, just prior to the R fireball event, in DNs. G_DATA.TAB: Raw DNs versus time for pixels containing the G impact site. R_DATA.TAB: Raw DNs versus time for pixels containing the R impact site. SI_G_1.TAB: Source intensities versus time for the G event using chi squared minimization for the fireball period, which finds the fraction (eta) of reflected light to subtract to obtain the best fit of a blackbody spectrum. A regression fit of eta to detector 1 was developed from the fireball period and applied to the pre- and post-fireball periods. SI_G_2.TAB: Same as above, but the regression algorithm found in the chi squared minimization was used for all data, including the fireball period. This is to test the sensitivity of the results to the analysis procedure. SI_R_2.TAB: Same as above, but for the R event. Ancillary Data ============== A Postscript-format Guide to the planned observations, including footprint plots on the target, instrument parameters, etc. is included in the data set, as are tables of parameters for each observation. A preprint of the NIMS instrument paper [CARLSONETAL1992] is also included. (These may be found under the DOCUMENT directory on the volume.) Calibration files, average dark value files and certain SPICE files (spacecraft positions, planetary positions and constants, processed pointing geometry, spacecraft clock versus universal time, etc.) were used in processing the NIMS data but are not included in the dataset. (They will be published in a separate volume at a later time.) However calibration information is present in one of the tables. Software ======== The tables are formatted for easy ingestion by PDS table tools, by most database software, or by simple user-written programs. Media/Format ============ The SL-9 tables are archived on CD-ROM for distribution by the Planetary Data System (PDS). Formats are based on standards for such products established by PDS. Specifically, the discs are formatted according to the ISO 9660 level 1 Interchange Standard, and file attributes are specified by Extended Attribute Records (XARs)." CONFIDENCE_LEVEL_NOTE = " Confidence Level Overview ========================= The usual discussion of confidence levels of NIMS data does not apply to this limited and unusual dataset. Pointing geometry is irrelevant, since Jupiter subtends only a single NIMS field-of-view, and all nonzero pixels are included in the analysis according to the theoretical portion of Jupiter they arise from. There is no noticeable noise in the data. However the detector sensitivities, determined from ground calibration as corrected by flight calibrations at Gaspra and Ida, have the usual uncertainties. Review ====== Data received from the SL9 encounter was so limited it could be reviewed by the NIMS team datum by datum. Format and documentation of the archived dataset was reviewed by several NIMS team members, then by MIPS personnel, who formatted the ancillary files according to ISO 9660 standards and wrote the CDWO, and finally by PDS before mastering. Data Coverage and Quality ========================= Information about the SL9 observations, and the data returned, are collected in a NIMS Guide to the encounter, included on the CD-ROM. Limitations =========== The calculated best estimate source intensities of Jupiter after the impact, in tables SI_G_1.TAB, SI_G_2.TAB and SI_R_2.TAB, are accompanied by lower and upper limit intensities, based on the intrinsic noise of the instrument and pointing-induced variations within a spectrum. See the labels of these tables for details." END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = JUPITER END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_TARGET TARGET_NAME = SKY END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = GO INSTRUMENT_ID = NIMS END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "CARLSONETAL1992" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "CARLSONETAL1995A" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "CARLSONETAL1995B" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "CARLSONETAL1997" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END