Data Set Overview : This data set has been generated by NASA's Galileo Project in order to distribute the images acquired by the Solid State Imaging (SSI) camera to the scientists and later to the Planetary Data System (PDS). The collection resides on volume GO_0016 and consists of all images acquired by the Galileo spacecraft during the period from the flyby of Ida through the Shoemaker-Levy 9 (SL9) comet impact on Jupiter. This includes data from SCLK 197327200 through 249221800 and contains the following targets: stars, Ida and Jupiter.   Ida Overview ------------ The Ida science data return plans and resulting spacecraft sequences were complex due to several factors including among others, uncertainty in the relative location of Ida and the spacecraft, uncertainty in spacecraft attitude and instrument pointing and downlink data rate constraints. At the outset, it was decided to return Ida data only when the telecommunications downlink supported 40 bps telemetry rate. Due to the limited time available for data playback at 40 bps, the intent was to identify and return only the highest priority data.  The playback of Ida data was accomplished by spacecraft stored sequence control. Sequences included a preview of the data on the tape recorder (Jailbar Search) so that the high priority data could be located for later return. On the basis of the jailbar search data, mini-sequences were developed to control the positioning of the tape within the tape recorder so that the desired data would be transferred from the tape recorder to the central computer and then to the ground.   SL9 Overview ------------ During Shoemaker-Levy 9 (SL9), multiple exposures of Jupiter were acquired on the CCD array by simultaneously slewing the scan platform and activating the shutter while suppressing CCD read-out. The resulting multiple exposure image is called an on-chip mosaic (OCM), and is referred to as the readout frame or playback image. Each of the single exposures within the OCM is called a shutter event.  The intent of the SL9 Data Return Strategy was to return a key subset of the acquired data based upon successive refinement of the comet fragment impact timing uncertainties. This goal was achieved through the use of two types of OCM observation patterns, diagonal scan and discrete shutter events, and the use of Jail Bar data playback techniques. These data acquisition approaches are described in the Parameters Section.   Parameters :  Ida Data -------- The Galileo SSI camera acquires data in a digital raster-format containing 800 scan lines and 800 samples per scan line. Each picture element (pixel) in the two dimensional image array is represented as an 8-bit value between 0 and 255, proportional to the amount of light detected at that point (with 0 being the least amount of light and 255 being the greatest amount of light). The camera is equipped with seven color filters and a clear filter such that images taken through complementary filters can be combined during ground processing to produce color images. To make full scientific use of the image collection, the radiometric and geometric properties of the camera system should be understood.  The ancillary disc, GO_0001, will provide calibration files and technical documentation necessary for the understanding of the images produced by the SSI camera. Presently, calibration files and software are available through the VICAR software system at MIPS and SPICE files are available through the Galileo Science Data Team.   SL9 Data Acquisition - Diagonal Scan ------------------------------------ Impacts K and N were observed with a pattern of 6 25-second diagonal scans, one scan per OCM shuttering, followed by CCD readout in the HCM mode. This pattern used the CCD as a tracing photometer, as the images of Jupiter were deliberately smeared across many pixels. Impact signatures can therefore be observed as brighter pixels in the smear, and at finer time resolution than the fastest 2-1/3 second shuttering mode. The pattern occupies approximately 1/3 of the SSI field of view. The SCLKs of the six playback images for the impact K OCMs are: 248806645, 248807000, 248807300, 248807700, 248808045 and 248808400. The SCLKs of the three playback images for the impact N OCMs are: 248949900, 248950200 and 248950600.   SL9 Data Acquisition - Discrete Shutter Events ---------------------------------------------- Impact W was observed with a discrete 8x8 pattern of 2-1/3 second OCM shutterings, followed by CCD readout in the IM4 mode. This pattern leaves (nominally) 40 pixels between each 60 pixel image. Each discrete image of Jupiter represents one point in a 2-1/3 second time series of data points, with one readout (or playback image) providing up to 64 discrete data points. In this manner, the time domain is translated into the spatial domain in the image. Fifty-six of the shutter events are within the field of view (FOV) in each playback image. The SCLKs of the playback images for the four discrete OCMs are: 249220555 (40 shutter events within the FOV played back), 249221000, 249221400 and 249221800.   SL9 Data Acquisition - Jail Bar Data Playback --------------------------------------------- The Jail Bar Searches (MCLAUGHLIN1994) were used to locate the actual image shuttering and scanning pattern within each SSI FOV (the locations of which varied from the nominal due to scan platform pointing uncertainties) and also to provide a correspondence between the image data and locations on the spacecraft tape. The Jail Bar Searches guaranteed return of two image lines out of every 80 for the diagonal scans and two lines of 40 for the discrete images. The images returned during Jail Bar Searches were selected based upon ground observations and timing information available from other spacecraft instruments.  Based upon the results of the Jail Bar Searches, the discrete shuttering events were subjected to a Jail Bar Return of up to eight 40 to 50 line swaths per frame for the four frames returned. The Jail Bar Returns for the diagonal scan observations returned four lines (guaranteeing two) out of every eight. See Processing Section (SL9-Specific Processing) for information about additional data recovery of lines for the diagonal scans.   SL9 Signal to Noise Ratio ------------------------- In order to improve the quality of data returned, the Deep Space Network sometimes used Block V Receivers to capture the data. This improved the quality of data returned, but impacted the reliability of the signal to noise ratio value recorded in the binary line prefix of the REDR images.   Processing :  REDR Processing --------------- The Raw Experiment Data Records (REDRs) were produced by the Multimission Image Processing Subsystem (MIPS) at the Jet Propulsion Laboratory using several Video Image Communications and Retrieval (VICAR) programs. The processing included the following steps:  --The original telemetry data was processed into raster-formatted files (GLLTELEMPROC)  --Multiple versions of each data file obtained from separate downlinks or playbacks were merged together to create the best version of the data (SSIMERGE)  --The VICAR label was updated to reflect the most recent pointing information (CATLABEL)  --Bad data value information was then added to the Telemetry Header (BADLABELS)  --Missing line gaps of two lines or less were filled in, as specified by the SSI Team. (GLLFILLIN)  --The PDS Index table and detached PDS label files were generated. (CDGEN)  --The VICAR files and PDS files were premastered onto a WORM CD-ROM which was validated.  --The WORM CD-ROM was sent to a vendor and CD-ROM's were generated.  --A final CD-ROM was compared bit-by-bit with the original data to ensure the quality of the vendor product.   SL9 Special Processing ---------------------- To maximize the data return from the diagonal scan playbacks, the telemetry data was massaged so the MIPS Real-Time Subsystem would process embedded lines not normally recovered from HCM playbacks. As a result, the number of returned image lines doubled. A side-effect of this process introduced artifacts which appeared in the form of an entire (formerly blank) line of pixels set to DN value 255. These lines were nullified by setting the affected pixel DN values to 0. Nullified lines are identified in the VICAR label of the affected images.  Dominating Reed-Solomon errors also existed in the diagonal scan playback images. At the request of the SSI team, partial lines were nullified to minimize the distracting visual effects of these errors. These nullified partial lines are also recorded in the VICAR label.   Data : The volume contains approximately 800 images stored as VICAR files. A detached PDS label has been included for each image. Documentation files have been provided which inform the user about the organization and contents of the disc, and the definition of the labels. An index files have also been provided which contain information about the images in the data set.  The REDR data are generated by MIPS using procedures specifically developed or adapted for Galileo. The files are generated on a VAX and are written in VAX compatible (LSByte first) format.   REDR File Format ---------------- The Galileo REDR format (WHITE1993) was originally reserved for SSI calibration data or data which should not be radiometrically corrected. The SSI Team recently decided that the REDR format will be used to archive all raw SSI data.  Each REDR file consists of a VICAR label, the telemetry header, the bad-data value header records (if there are any), and the Image Data which is preceded by a Binary Prefix. There are 800 line records of image data. All records are fixed length. The line record length is 1000 bytes; 200 bytes of a binary line prefix and 800 bytes of 8 bit pixel data. (Note, for the AI8 format or summation mode, the record length is still 1000, but the data is placed in the first 400 pixel samples and 400 lines only.) There will be a one-to-one correspondence between line records and image lines. Data not received will be zero-filled.  The BINARY HEADER is composed of a Telemetry header and a Bad-Data Value Header containing ancillary information specific to the image. The TELEMETRY HEADER is split into two physical records. The first 1000 bytes are placed in the first physical record after the VICAR label, and the last 800 bytes are placed in the next physical record. The last 200 bytes are zero filled. The BAD-DATA VALUE HEADER is composed of records describing several types of bad data values. Each record describes only one type and depending on the number of bad pixels, they may span over several physical records. Each record is identified by the Record IDS field which is located at byte 0.   Ancillary Data : All document files and detached label files contain a carriage return character (ASCII 13) and a line feed character (ASCII 10) at the end of each record. This allows the files to be read by the MacOS, DOS, Unix, and VMS operating systems. Tabular files are also described by a detached PDS label. The PDS label file has the same name as the data file it describes, with the extension .LBL; for example, the file IMGINDEX.TAB is accompanied by the detached label file IMGINDEX.LBL in the same directory. The detached PDS labels for REDR images contain information pertaining to the image.  Tabular files are formatted so that they may be read directly into many database management systems on various computers. All fields are separated by commas, and character fields are enclosed in double quotation marks. Character fields are left justified, and numeric fields are right justified. The start byte and bytes values listed in the labels do not include the commas between fields or the quotation marks surrounding character fields. The records are of fixed length, and the last two bytes of each record contain the ASCII carriage return and line feed characters. This allows a table to be treated as a fixed length record file on computers that support this file type and as a normal text file on other computers.   SL9 Special Handling of Ancillary Information --------------------------------------------- Due to the OCM images in the SL9 data set ancillary information required special handling.  In the past, the telemetry format for the SSI instrument data matched the telemetry format for the spacecraft, so the spacecraft telemetry format was automatically recorded in the data labels. During the OCM process, the camera operated independently and under a different telemetry format than the spacecraft. In the PDS and VICAR labels for the SL9 data set, the SSI telemetry format is provided.  The imaging mode provided by the NAIF mini-e kernel for the first shutter event included in each of the discrete playback images had the value of the imaging mode of the playback image (8-2/3), not the shutter event. This value was manually modified to reflect the shutter events' imaging mode (2-1/3).  In theory, the exposure duration of the playback images should be 0, but this would hinder subsequent image processing, such as radiometric correction. Therefore the EXPOS_TIME for the playback images has been set to match the exposure time of the shutter events.   SL9 Graphics Files ------------------ A graphics file corresponding to each playback image has been generated to simplify the identification of shutter event PICNOs within playbacks. The graphics files were generated by contrast enhancing a copy of the playback image to make the target more visible, then overlaying the text information onto the image. Due to the quantity of shutter events within the playbacks, in order to make the graphics file readable, only the last four digits of the PICNOs are used in the graphics file to identify shutter events. Although the files have been called graphics files they are still VICAR files with the same data format as the REDR.   Each graphics file and its detached PDS label is located in the same directory as the corresponding playback image, and will have essentially the same filename as the playback, except the last character will be a G instead of an R.   SL9 Index File -------------- An additional text file, SL9INDEX.TXT (also located in the INDEX directory) has been generated which provides the spacecraft clock rim and mod91, Earth Observation Time (EOT), playback image filename, graphics filename, and a (line,sample) location of each shutter event. The EOT is the time (UTC) that an Earth observer would have witnessed an event on Jupiter that was observed by the spacecraft during the specified shutter event. The EOT is calculated by starting with the time at shutter midpoint, subtracting one-way light time to the subspacecraft point on Jupiter, and adding one-way light time from Jupiter to the Earth. For the diagonal scans, the (line,sample) is a point roughly in the center of the slew, and for the discrete shutter events, the (line,sample) is a point on Jupiter.   Software : The following CD-ROM copy, display and processing software has been successfully tested using the Galileo SSI data:   Copy Software ------------- --DCL COPY (VMS) - available with VMS --VICAR Copy (VMS and UNIX) - Available with VICAR package from COSMIC.   Display Software ---------------- --VICAR JDISP (VMS and UNIX) - Available with VICAR package from COSMIC.  --PIXEL PUSHER (Apple Macintosh) - Available from COSMIC.  --NIH IMAGE (Apple Macintosh) - A public domain program available from the National Institute of Health.  --CDBROWSE (UNIX/Motif) - Software may be obtained from richard@ben.jpl.nasa.gov on the internet.  --IMDISP (IBM PC) - Program and information about this program are available from PDS.   Processing Software ------------------- --VICAR (VMS and UNIX) - Available from COSMIC --ISIS (VMS and UNIX) - Available through the USGS in Flagstaff   Media/Format : Each CD-ROM disc has been formatted such that a variety of computer systems may access the data. Specifically, the discs are formatted according to the ISO 9660 level 1 Interchange Standard, and file attributes are specified by Extended Attribute Records (XARs). Formats are based on standards for archive EDR CD-ROM products established by PDS.

Confidence Level Overview : The SSI REDRs contain raw data as received from Galileo telemetry. All 120 of the images received were processed and are contained on this volume. Included in the limitations section are explanations of the VICAR and PDS keywords and values, as well as a description of a problem found with one frame in the data set. This data set contains all of the data acquired during the Ida and Shoemaker-Levy 9 period, the processing has been verified, and is currently in use by science team members in their analysis   Review : The SSI REDRs are reviewed prior to archiving by the SSI team. Data received is compared with data expected, and replays of missing data is requested. The status and validity information on the REDRs themselves is examined. Format and documentation of the CD-ROM archive volume is reviewed by PDS and is documented in WAINIO1992. The mastered and replicated CD-ROM volumes received from the vendor are compared bit-by-bit with the original data to ensure the quality of the product.   Data Coverage And Quality : Sequences and Objectives:  The SSI team correlates sequences of images with imaging and science objectives through the use of Activity Ids. Below are the SSI Activity Ids and their objectives for the Shoemaker-Levy 9 data set..  OPNAV_02_XCAL optical navigation during Ida approach OPNAV_04_XCAL optical navigation during Ida approach OPNAV_05_XCAL optical navigation during Ida approach IDUSROTATI01003IDAB Ida rotation movie 1 IDUSROTATI02018IDAC Ida rotation movie 2 IDUSFINROT01100IDAC Ida rotation movie IDUS6COLOR01111IDA6 Ida target for 6-color 1X1 and 4-color 2X2 IDUNIDACHM01115IDAS Ida composition at 102 wavelength IDUSHIRES_01120IDAH Ida HiRes 95% confidence observation SLJIMPCTK01 SL9 impact K, diagonal slew SLJIMPCTN01 SL9 impact N, diagonal slew SLIMPCTW01 SL9 impact W, discrete shutter events   Limitations : General Information:  This section documents the currently known bad images, saturated frames and any problems which have currently been identified in the Ida and Shoemaker-Levy 9 data sets. For the purpose of this memo CD refers to the SSI REDR CD-ROM GO_0016. There were 120 frames received and processed.  The following datasets are included on the CD. The starting and ending SCLK's have been identified, as well as any general information that might be needed to document the dataset.   IDA OPNAV --------- SCLKs 197327200 thru 201554000 - VICAR/PDS labels incomplete due to lack of SPICE info. - Activity id not in standard format   IDA --- SCLKs 202530700 thru 202562800 - SPICE info available   SHOEMAKER-LEVY 9 ---------------- SCLKs 248806645 thru 249221800 - SPICE available  It should be noted that the processing for this dataset was identical for each file; (only bad data values were identified).   VICAR Labels ------------ Definitions for VICAR field names can be found in WHITE1993.  A) The RAD field (ring radius at frame center) within the VICAR label was not applicable and is equal to 0.0, for the CD.  B) The following fields in the VICAR label were not implemented for the entire CD. The current values are listed below.  HRA : -999.0 SMEAR : -999.0 SMRAZ : 0.0 SOLRANGE (Calib. frames only) : 7.779091  C) For targets other than a planetary body or asteroid (e.g. black sky, stars, calibration etc.) most pointing information is not available. A listing of the missing fields is provided below. More detailed information can be found in the CATSTAT.TXT file which located in the DOCUMENTS directory on all of the CD's. These fields are also missing if no corresponding SPICE SP information is available for an image. The current values are listed below.  EMA : -999.0 PHA : 0.0 INA : -999.0 LAT : 0.0 LON : 0.0 TCA : 'closest time' HSCL : -999.0 VSCL : 0.0 PLRANGE : 0.0 SLRANGE : 0.0 SUNAZ : 0.0 NORAZ : 0.0 SCAZ :0.0 SOLRANGE : 7.779091  D) PLRANGE is now always equivalent to the spacecraft central body range.   PDS Labels ---------- Definitions for PDS field name can be found in CRIBBS1992.  A) The following PDS fields were not applicable for the entire CD. The current values are listed below.  BLEMISH_FILE_NAME : 'N/A' CENTER_RING_RADIUS : 0.0 DARK_CURRENT_FILE_NAME :' N/A' EDR_FILE_NUMBER :' N/A' EDR_TAPE_ID : 'N/A' MEAN_RADIANCE : 'N/A' MEAN_REFLECTANCE : 'N/A' ORBIT_NUMBER : 'null' or 20559 or 17481 RADIANCE_SCALING_FACTOR : 'N/A' REFLECTANCE_SCALING_FACTOR : 'N/A' SHUTTER_OFFSET_FILE_NAME : 'N/A' SLOPE_FILE_NAME : 'N/A' UNEVEN_BIT_WEIGHT_CORR_Flag : 'N/A'  B) SPICE_FILE_NAME was changed to SOURCE_PRODUCT_ID. If the kernel was not available, it was identified as NULL.  C) The following PDS fields were not implemented for the entire CD. The current values are listed below.  LOCAL_HOUR_ANGLE : 'unk' SMEAR_AZIMUTH : 0.000 SMEAR_MAGNITUDE : 'unk' SOLAR_DISTANCE Calibration Only : 7.779091  D) For targets other than a planetary body or asteroid (e.g. black sky, stars, calibration etc.) or if the SPICE SP information is missing, the following pointing information is not available in the PDS labels .  A_AXIS_RADIUS : 'unk' B_AXIS_RADIUS : 'unk' CENTER_LONGITUDE : 0.00000 CENTRAL_BODY_DISTANCE : 0.00000 EMISSION_ANGLE : 'unk' HORIZONTAL_PIXEL_SCALE : 0.00000 INCIDENCE_ANGLE : 'unk' NORTH_AZIMUTH : 0.000 PHASE_ANGLE : 'unk' SATELLITE_TIME_FROM_CLST_APR : 'unk' SLANT_DISTANCE : 0.00000 SUB_SOLAR_AZIMUTH : 0.000 SUB_SOLAR_LONGITUDE : 'unk' SUB_SPACECRAFT_AZIMUTH : 0.000 SUB_SPACECRAFT_LATITUDE : 'unk' SUB_SPACECRAFT_LINE : 'unk' SUB_SPACECRAFT_LINE_SAMPLE : 'unk' SUB_SPACECRAFT_LONGITUDE : 'unk' TARGET_CENTER_DISTANCE : 'unk' TIME_FROM_CLOSEST_APPROACH : 'unk' VERTICAL_PIXEL_SCALE : 0.00000  E) ORBIT_NUMBER for frames between 197327200 through 202562800 incorrectly reads 20559 or 17481 instead of UNK.  F) A few new keywords were added. They are POSITIVE_LONGITUDE_ DIRECTION, ^LINE_PREFIX_TABLE, INTERCHANGE_FORMAT in the Vicar Image Header Object, and TYPE in the Bad Data Value Header Object   PDS Index Table --------------- A) The following fields in the PDS Index table were not applicable for the entire. The current values are listed.  CENTER_RING_RADIUS : 0.0 MEAN_RADIANCE : 'N/A' MEAN_REFLECTANCE : 'N/A' ORBIT_NUMBER : 'unk' or 205 or 174 RADIANCE_SCALING_FACTOR : 'N/A' REFLECTANCE _SCALING_FACTOR : 'N/A'  B) The following fields in the PDS Index table were not implemented for the entire. The current values are listed here.  LOCAL_HOUR_ANGLE :'unk' SMEAR_AZIMUTH : 0.000 SMEAR_MAGNITUDE : 'unk' SOLAR_DISTANCE Calibration only : 7.779091  C) For targets other than a planetary body or asteroid (e.g. black sky, stars, calibration etc.) or the corresponding SPICE SP information is missing, some pointing information is not available. A listing of the missing fields is provided below.  CENTER_LATITUDE : 0.00000 CENTER_LONGITUDE : 0.00000 CENTRAL_BODY_DISTANCE : 0.00000 EMISSION_ANGLE : 'unk' HORIZONTAL_PIXEL_SCALE : 0.00000 INCIDENCE_ANGLE : 'unk' NORTH_AZIMUTH : 0.000 PHASE_ANGLE : 'unk' SATELLITE_TIME_FROM_CLST_APR : ' unk' SLANT_DISTANCE : 0.00000 SUB_SOLAR_AZIMUTH : 0.000 SUB_SOLAR_LATITUDE : 'unk' SUB_SOLAR_LONGITUDE : 'unk' SUB_SPACECRAFT_LATITUDE : 'unk' SUB_SPACECRAFT_LINE : 'unk' SUB_SPACECRAFT_LINE_SAMPLE : 'unk' SUB_SPACECRAFT_LONGITUDE : 'unk' TARGET_CENTER_DISTANCE : 'unk' TIME_FROM_CLOSEST_APPROACH : 'unk' VERTICAL_PIXEL_SCALE : 0.00000  D) In the TARGET field of the index file, there is a limitation to 10 characters which caused NON_SCIENCE to appear as NON_SCIENCE. The PDS labels contain the full target name.   Reed-Solomon Overflow --------------------- Reed-Solomon overflows were not removed in this dataset via processing. Most of the overflows have been identified within this dataset in the Binary Line Prefix of the VICAR label. Due to a known anomaly, a small percentage of the Reed-Solomon errors may have failed to be flagged in the Binary Prefix.  The Reed-Solomon overflow may occur in images which were Reed-Solomon encoded by the Galileo spacecraft. If the data was received on the ground and the Reed-Solomon decoder was unable to completely decode the data, this overflow feature is present in the data.  The Reed-Solomon overflow feature may be identified by the following criteria. It is present on a single line or series of lines. It starts about midway through a line and always continues through sample 800. The data numbers (dn's) can shift between white, black or shades of gray. In some cases, the dn's may be just a few dn brighter or darker than the surrounding lines. Reed-Solomon overflows should not be confused with the data gaps caused by the decompression of data. Decompression gaps are usually at the extreme right of an image, they always have a dn:0 (black) and they are clearly identified in the VICAR Binary Prefix.   Additional Failures Discovered in the Data Set ---------------------------------------------- A) TIME_FROM_CLOSEST_APPROACH and SATELLITE_TIME_FROM_CLST_APR are not in the standard DATE/TIME format. Since they are not a date and only a time, PDS is in the process of defining a new data type for these keywords. PDS software is being modified to handle this.  B) The REDR file GO_0016:[ida.C020256]1945R.IMG contains extraneous data on lines 378 and 379, which should be dark sky. A redo of this image will be published on the next REDR CD.