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Space Topics: Cassini-Huygens

Cassini ISS Image Database

*NEW* Database has been entirely updated and corrected as of October 1, 2011 PDS release

To date, Cassini's Imaging Science Subsystem has acquired more than 270,000 images. When these data are made available via the Planetary Data System, the mission includes vast tables of metadata describing the timing, geometry, camera settings, and other features of the images. The metadata tables are split up, volume by volume. Imaging enthusiast Björn Jónsson has taken these metadata tables and created a Microsoft Access formatted database to all of Cassini's images, making it easier to search for images that match certain requirements. The database includes a few sample queries to help you get started. The Planetary Society is happy to host this database and make it available for download.

This database includes information on all images released as of October 1, 2011, and includes fixes to issues identified in the ERRATA.TXT files on each archive volume. Users who downloaded any previous version of this database are encouraged to begin again with this database. The database includes some useful sample queries that will produce lists of images of specific targets, with specific filters, and/or specific phase angles. "wget" queries will return lists of links to image files that can be used with the Gnu Wget program to batch download images of interest from the PDS.

Other useful links: Planetary Society browse pages to Cassini images of Saturn's moons; Björn Jónsson's index page to what's of interest on the Cassini image DVDs; the searchable Cassini raw images website; the PDS data can be downloaded from the PDS through the online DVD volumes or through the searchable Planetary Image Atlas.

What's in the Metadata?

Following are definitions of each of the column headers taken from the Cassini DVDs.

FILE_SPECIFICATION_NAME - Path name locating images in DATA directory on data set volumes.

VOLUME_ID - The volume on which the product is stored.

ANTIBLOOMING_STATE_FLAG - Indicator of whether antiblooming was used for this image.

BIAS_STRIP_MEAN - Mean value of the overclocked pixel values from all lines except the first and last. Not affected by light or dark current.

CALIBRATION_LAMP_STATE_FLAG - Indicates whether calibration lamp was used for this image. (ISSNA has none, so it's always 'N/A')

COMMAND_FILE_NAME - The name of the IOI file containing the observation description for this product - sent from the ISS Team Lead to IO.

COMMAND_SEQUENCE_NUMBER - Numeric identifier for a sequence of commands sent to the spacecraft. Also known as 'trigger number'. (Comes from the TRIGGER_NUMBER keyword in the IOI file.) Note that 1-12 are reserved for IO use and 8 is reserved for OpNav.

DARK_STRIP_MEAN - Mean value of the extended pixel values from all lines except the first and last. Not affected by light, but by dark current and Dark Band problem.

DATA_CONVERSION_TYPE - The method of conversion used to convert image from 12 to 8 bits selected for this image. '12BIT' = no conversion 'TABLE' = conversion by look-up table '8LSB' = keep only the 8 least significant bits

DATA_SET_ID - PDS/Cassini-supplied name for this data set.

DELAYED_READOUT_FLAG - Indicator of whether the image may have waited on the CCD while the other camera was performing a readout.

DESCRIPTION - Descriptive comment up to 255 characters. Populated by IO telemetry processing, validation and reconciliation software to describe known limitations of this product.

DETECTOR_TEMPERATURE - Temperature of CCD in Celsius degrees.

EARTH_RECEIVED_START_TIME - Earth Received time of the earliest record containing valid data for this image (UTC).

EARTH_RECEIVED_STOP_TIME - Earth Received time of the latest record containing valid data for this image (UTC).

ELECTRONICS_BIAS - Commanded electronics bias to ensure that all DN values are greater than zero. (Comes from the VIDEO_OFFSET keyword in the IOI file.)

EXPECTED_MAXIMUM - 2-valued array. First, represents the ratio of the expected maximum DN in the image to the VALID_MAXIMUM (full well DN). Second, represents the ratio of the expected maximum DN in the image to the VALID_MAXIMUM (maxDN).

EXPECTED_PACKETS - This keyword provides the total number of packets expected to be stored on the SSR for this image. To convert to volume in bits, multiply this value by 7616 bits/packet. (Comes from the EXPECTED_PACKETS keyword in the IOI file.)

EXPOSURE_DURATION - Exposure duration for the image in milliseconds. 63 distinct values from 0 to 1200000. (See table in AppendixA.) -999.0 if extended header is unavailable

FILTER_NAME - 2-valued array. First, filters used on filter wheel 1. Second, filters used on filter wheel 2.

FILTER_TEMPERATURE - Temperature of the filter wheels.

FLIGHT_SOFTWARE_VERSION_ID - Indicates version of instrument flight software used to acquire image.

GAIN_MODE_ID - The electronics gain setting selected for this image, given in units of electrons per DN. (This is an approximate value so both cameras can use the same set of values.)

IMAGE_MID_TIME - Exposure mid-time calculated from spacecraft clock using both the coarse (seconds) and fine (subRTI) counters (UTC). (A subRTI is approximately 4 msec (1/256 second)). This value is calculated from the SPACECRAFT_CLOCK_STOP_COUNT - (EXPOSURE_DURATION/2) then converted to UTC. When the shutter was inhibited (ie SHUTTER_STATE_ID='DISABLED'), the IMAGE_MID_TIME = START_TIME = STOP_TIME, and all three represent the start of the exposure window during the prepare cycle of the image.

IMAGE_NUMBER - The seconds portion of the spacecraft clock at shutter close.

IMAGE_OBSERVATION_TYPE - A multi-valued list describing the purpose(s) of this image, for example, OPNAV, science, calibration, engineering and/or support imaging. (Comes from the IMAGE_OBSERVATION_TYPE_* keywords in the IOI file parameter set description.) This list can contain up to five values where the purposes of the image are identified. More than one value may be specified.

IMAGE_TIME - Time of shutter close calculated from spacecraft clock using both the coarse (seconds) and fine (subRTI) counters (UTC). (A subRTI is approximately 4 msec (1/256 second)). When the shutter was inhibited (ie SHUTTER_STATE_ID='DISABLED'), the IMAGE_TIME = START_TIME = STOP_TIME, and all three represent the start of the exposure window during the prepare cycle of the image.

INSTRUMENT_DATA_RATE - The rate at which data was transferred out of instrument. -999.0 if channelized data and extended header are unavailable.

INSTRUMENT_HOST_NAME - Name of the spacecraft upon which this instrument resides.

INSTRUMENT_ID - Indicator of which camera took this image.

INSTRUMENT_MODE_ID - The summation mode used for this image.

INSTRUMENT_NAME - Name of the CASSINI Instrument which acquired the image data.

INST_CMPRS_PARAM - 4-valued array. First, the lossy compression MALGO (algorithm) parameter. MALGO. Second, the lossy compression TB (block type) parameter. TB. Third, the lossy compression group-of-blocks (number of blocks per group) parameter. GOB. Fouth, the lossy compression the compression rate parameter (quantization factor). QF.

INST_CMPRS_RATE - 2-valued array. First, the expected average number of bits and comes from the BITS_PER_PIXEL keyword in the IOI file. Second, the actual average number of bits and is calculated during telemetry processing.

INST_CMPRS_RATIO - Ratio of expected image size to size of image received. (Calculation of this value does not include data outages due to truncated readouts or data lost in transmission.)

INST_CMPRS_TYPE - Compression type used for the image.

LIGHT_FLOOD_STATE_FLAG - Indicator of whether Light Flood was used just prior to taking this image.

METHOD_DESC - This keyword describes the information and/or algorithm used to calculate the I/F value used by the ISS team to determine the EXPOSURE_DURATION. (Limited to char(75)). (Comes from the METHOD_DESC keyword in the IOI file.)

MISSING_LINES - For non-lossy compressed data only, number of missing or incomplete image lines. For all data, including lossy compressed images, when data is missing, the missing pixel values are replaced by 0. 'N/A' for lossy compressed data.

MISSING_PACKET_FLAG - Indicator of whether consecutive packets were received. If set to 'YES', this flag indicates that packets needed to construct a complete image were missing. If set to 'NO', all consecutive packets were received. However, data may be missing at the beginning or end of the image. In this case, missing data would be reflected in the MISSING_LINES keyword for non-lossy data, and through visual inspection for lossy compressed data.

MISSION_NAME - Mission name associated with this image.

MISSION_PHASE_NAME - Mission phase of which this image is a part.

OBSERVATION_ID - Name of observation of which this image is a part.

OPTICS_TEMPERATURE - 2-valued array. First, temperature of front optics in Celsius degrees. Note that there is no rear optics temperature for the WAC camera, so when INSTRUMENT_ID = ISSWA, the second element of the array will always be -999.0. (-999.0, -999.0) if the extended header is unavailable. Second, temperature of rear optics in Celsius degrees. Note that there is no rear optics temperature for the WAC camera, so when INSTRUMENT_ID = ISSWA, the second element of the array will always be -999.0. (-999.0, -999.0) if the extended header is unavailable.

ORDER_NUMBER - Identifier provided by Team Lead for this image which is unique within the IOI file. This value will not be unique for parameter sets described in the IOI file with ITERATION_COUNT > 1 or with LOOP_COUNT > 1

PARALLEL_CLOCK_VOLTAGE_INDEX - Commanded parallel clock voltage index. Controls clocking frequency. (Comes from the PC_VOLTAGE keyword in the IOI file.)

PREPARE_CYCLE_INDEX - The element number within the Prepare Cycle table selected for this image. (see Appendix B tables)

PRODUCT_CREATION_TIME - Time of creation of this image on the ground (Pacific local time).

PRODUCT_ID - Unique identifier for each image commanded. Required by PDS/Cassini. The PRODUCT_ID will be constructed: SPACECRAFT_CLOCK_CNT_PARTITION'_'ISPACECRAFT_CLOCK_STOP_COUNT, where I is 'N' if the INSTRUMENT_ID is 'ISSNA', and I is 'W' if the INSTRUMENT_ID is 'ISSWA'.

PRODUCT_VERSION_TYPE - Identifies the version of an individual data product. Always 'FINAL' for products archived with PDS/Cassini. 'PRELIMINARY' indicates additional processing is underway at IO/MIPL, for instance, to recover additional telemetry if possible.

READOUT_CYCLE_INDEX - The element number within the Readout Cycle table selected for this image. (see Appendix B tables)

RECEIVED_PACKETS - This keyword provides the actual number of packets received from the SSR for this image. To convert to volume in bits, multiply this value by 7616 bits/packet. This value reflects data received. In the event the image is incomplete due to an outage in the transmission, this field will not be an accurate indicator of actual volume on the SSR.

SENSOR_HEAD_ELEC_TEMPERATURE - Temperature of the sensor head electronics.

SEQUENCE_ID - Identifies the segment associated with this image. Note that this keyword does not come from the IOI file. Ex: 'C22', 'S19'

SEQUENCE_NUMBER - Indicates the order in which this image was expected to be taken within the given observation (OBSERVATION_ID).

SEQUENCE_TITLE - The name assigned by the Team Lead for the activity of which this image is a part. Comes from the SEQUENCE_TITLE keyword in the IOI file. Limited to 30 characters. Example = ???.

SHUTTER_MODE_ID - Indicator of whether this exposure was part of a joint observation with the other ISS camera.

SHUTTER_STATE_ID - Indicator of whether the shutter was enabled during the exposure.

SOFTWARE_VERSION_ID - Ground software version used to generate this image.

SPACECRAFT_CLOCK_CNT_PARTITION - Indicates the clock partition active for the SPACECRAFT_CLOCK_START_COUNT and SPACECRAFT_CLOCK_STOP_COUNT elements. Remains at '1' unless the spacecraft clock rolls over or is reset.

SPACECRAFT_CLOCK_START_COUNT - The seconds and subRTI portions of the spacecraft clock at shutter open. Calculated from spacecraft clock of shutter close less the exposure duration. When the shutter was inhibited (ie SHUTTER_STATE_ID='DISABLED'), the SPACECRAFT_CLOCK_START_COUNT = SPACECRAFT_CLOCK_STOP_COUNT, and both represent the start of the exposure window during the prepare cycle of the image. EX: '832898283.123'

SPACECRAFT_CLOCK_STOP_COUNT - The seconds and subRTI portions of the spacecraft clock at shutter close. (A subRTI is approximately 4 msec (1/256 second)). When the shutter was inhibited (ie SHUTTER_STATE_ID='DISABLED'), the SPACECRAFT_CLOCK_START_COUNT = SPACECRAFT_CLOCK_STOP_COUNT, and both represent the start of the exposure window during the prepare cycle of the image. EX: '832898284.456'

START_TIME - Time of shutter open. Calculated from spacecraft clock of shutter close less the exposure duration. Expressed in UTC format, and includes subRTI resolution. (A subRTI is approximately 4 msec (1/256 second)). When the shutter was inhibited (ie SHUTTER_STATE_ID='DISABLED'), the START_TIME = STOP_TIME, and both represent the start of the exposure window during the prepare cycle of the image. EX: 1996-158T05:53:34.000Z

STOP_TIME - Time of shutter close from spacecraft clock (UTC). Identical to IMAGE_TIME. Includes subRTI resolution. (A subRTI is approximately 4 msec (1/256 second)). When the shutter was inhibited (ie SHUTTER_STATE_ID='DISABLED'), the START_TIME = STOP_TIME, and both represent the start of the exposure window during the prepare cycle of the image. EX: 1996-158T05:53:34.000Z

TARGET_DESC - The name of the intended target for which the exposure was calculated/selected in the given image. May include calibration type information. Limited to 75 characters. (Comes from the TARGET_DESC keyword in the IOI file.)

TARGET_NAME - Identifies a target. The target may be a planet, satellite, ring, region, feature, asteroid or comet.

TELEMETRY_FORMAT_ID - The telemetry mode in effect when sending data from the instrument to the spacecraft computer.

VALID_MAXIMUM - 2-valued array. First, indicates the minimum full well saturation level of the instrument, which is a function of INSTRUMENT_MODE_ID, INSTRUMENT_ID, and GAIN_MODE_ID, expressed as a DN value. This may exceed 4095. Second, indicates the maximum DN saturation level for the signal returned by the A/D converter. Valid values are 255 and 4095. See Appendix B tables

CENTRAL_BODY_DISTANCE - Distance from spacecraft to center of primary body.

COORDINATE_SYSTEM_NAME - The full name of the coordinate system to which the state vectors are referenced.

DECLINATION - Declination of camera optic axis.

EMISSION_ANGLE - Emission angle at aimpoint on target.

INCIDENCE_ANGLE - Incidence angle at aimpoint on target.

LOWER_LEFT_LATITUDE - Planetocentric latitude of lower-left pixel.

LOWER_LEFT_LONGITUDE - West longitude of lower-left pixel.

LOWER_RIGHT_LATITUDE - Planetocentric latitude of lower-right pixel.

LOWER_RIGHT_LONGITUDE - West longitude of lower-right pixel.

MAXIMUM_RING_RADIUS - Maximum ringplane radius in image.

MINIMUM_RING_RADIUS - Minimum ringplane radius in image.

NORTH_AZIMUTH_CLOCK_ANGLE - Direction of the northward-pointing azimuth at the aimpoint on the target body, measured clock- wise.

PHASE_ANGLE - Phase angle at subspacecraft point on target.

PIXEL_SCALE - Size of one pixel at subspacecraft point on target body.

PLANET_CENTER - 2-valued array. First, Line of target body center. Second, Sample of target body center.

RIGHT_ASCENSION - Right ascension of camera optic axis.

RING_CENTER_LATITUDE - Planetocentric latitude at aimpoint on ring

RING_CENTER_LONGITUDE - West longitude at aimpoint on ring

RING_EMISSION_ANGLE - Emission angle relative to target ring northward- pointing normal at aimpoint.

RING_INCIDENCE_ANGLE - Incidence angle relative to target ring northward- pointing normal at aimpoint.

RINGS_FLAG - If any part of the A, B, C, D, E, F, or G ring is visible in the image, this quantity is 'YES'; 'NO' otherwise.

SC_PLANET_POSITION_VECTOR - 3-valued array. X, Y, Z components of the position vector from spacecraft to primary planet center, corrected for light-travel time and stellar aberration.

SC_PLANET_VELOCITY_VECTOR - 3-valued array. X, Y, Z components of the velocity vector of primary planet relative to spacecraft, corrected for light-travel time.

SC_SUN_POSITION_VECTOR - 3-valued array. X, Y, Z components of the position vector from spacecraft to sun center, corrected for light-travel time and stellar aberration.

SC_SUN_VELOCITY_VECTOR - 3-valued array. X, Y, Z components of the velocity vector of sun relative to spacecraft, corrected for light-travel time.

SC_TARGET_POSITION_VECTOR - 3-valued array. X, Y, Z components of the position vector from spacecraft to target center, corrected for light-travel time and stellar aberration.

SC_TARGET_VELOCITY_VECTOR - 3-valued array. X, Y, Z components of the velocity vector of the target relative to spacecraft, corrected for light-travel time.

SPICE_PRODUCT_ID - The names of the SPICE files used in processing the data.

SUB_SOLAR_LATITUDE - Planetocentric latitude of subsolar point on target; Ring_Subsolar_Latitude if target is a ring.

SUB_SOLAR_LONGITUDE - West longitude of subsolar point on target; Ring_Subsolar _Longitude if target is a ring.

SUB_SPACECRAFT_LATITUDE - Planetocentric latitude of subspacecraft point on target; Ring_Subspacecraft_Latitude if target is a ring.

SUB_SPACECRAFT_LONGITUDE - West longitude of subspacecraft point on target; Ring_Subspacecraft_Longitude if target is a ring.

CENTER_LATITUDE - Planetocentric latitude at aimpoint on target (or Ring_Aimpoint_Latitude if target is a ring).

CENTER_LONGITUDE - West longitude at aimpoint on target (or Ring_Aimpoint_Lo ngitude if target is a ring).

TARGET_DISTANCE - Distance from the spacecraft to the center of the target.

TARGET_EASTERNMOST_LONGITUDE - Easternmost longitude visible on target body.

TARGET_NORTHERNMOST_LATITUDE - Northernmost latitude visible on target body.

TARGET_SOUTHERNMOST_LATITUDE - Southernmost latitude visible on target body.

TARGET_WESTERNMOST_LONGITUDE - Westernmost longitude visible on target body.

TWIST_ANGLE - Twist angle of optic axis.

TARGET_LIST - Name of each body visible in the image. A body is included if any part of its limb is not hidden by another body. Bodies may be obscured by rings.

UPPER_LEFT_LATITUDE - Planetocentric latitude of upper-left pixel.

UPPER_LEFT_LONGITUDE - West longitude of upper-left pixel.

UPPER_RIGHT_LATITUDE - Planetocentric latitude of upper-right pixel.

UPPER_RIGHT_LONGITUDE - West longitude of upper-right pixel.

DATA_SET_NAME - The name given to the Cassini ISS EDR image data set.

INSTRUMENT_HOST_ID - Unique identifier for the host where the instrument is located.

PRODUCT_TYPE - Identifies the type of a data product within the data set.

STANDARD_DATA_PRODUCT_ID - Used to link a data product (file) to a standard data product (collection of similar files) described within software interface specification document for a particular data set.