| DATA_SET_DESCRIPTION |
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_NOTE |
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.
|
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