Data Set Information
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| DATA_SET_NAME |
CASSINI ORBITER RADAR LONG BURST DATA RECORD
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| DATA_SET_ID |
CO-V/E/J/S-RADAR-3-LBDR-V1.0
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| NSSDC_DATA_SET_ID |
|
| DATA_SET_TERSE_DESCRIPTION |
|
| DATA_SET_DESCRIPTION |
* Data Set OverviewBurst Ordered Data Products (BODP) are comprehensive data files thatinclude engineering telemetry, radar operational parameters, raw echodata, instrument viewing geometry, and calibrated science data. TheBODP files contain time-ordered fixed length records. Each recordcorresponds to the full set of relevant data for an individual radarburst. The Cassini Radar is operated in 'burst mode,' which means theradar transmits a number of pulses in sequence then waits to receivethe return signals. 'Burst' is a descriptive term for the train ofpulses transmitted by the radar. The term 'burst' (somewhatunconventionally) refers to an entire measurement cycle includingtransmit, receipt of echo, and radiometric (passive) measurements ofthe naturally occurring radiation emitted from the surface. In fact,even when the transmitter is turned off and only passive measurementsare made Burst Ordered Data Products are still fixed header length,fixed record length files.The header is an attached PDS label. Records are rows in a table.Each data field is a column. All one needs to know to read aparticular data value from a particular data field is the headerlength, the record size, and the byte offset of the data field withinthe record. Since a UTC time tag is included in each record, it is asimple matter to restrict the data one reads to a particular timeinterval.The BODP comprise three separate data sets, including the Short BurstData Record (SBDR), the Long Burst Data Record (LBDR), and the AltimeterBurst Data Record (ABDR). The only difference between the three formatsis whether or not two data fields are included: the sampled echo dataand the altimeter profile. The altimeter profile is an intermediateprocessing result between sampled echo data and a final altitude estimate.LBDRs include the echo data but not the altimeter profile. ABDRs includethe range compressed altimeter pulse profiles but not the echo data.SBDRs include neither. These trivial differences necessitate differentdata sets because the two fields in question are much larger than allthe other data fields combined. The majority of the bursts in a typicalTitan pass are passive measurements. These bursts do not produce echodata or altimeter profiles. Of the active mode bursts most are not inaltimeter mode so no altimeter profiles are produced. Including thesetwo data fields when they are invalid would ridiculously increase the sizeof the archived data. The alternative of having variable length recordswas deemed to overly complicate data archiving and analysis procedures.Maintaining three data sets reduces data volume while allowing recordlengths to remain fixed.The descriptions of each field in the records canbe found in the LBDR.FMT, SBDR.FMT, and ABDR.FMT files. These files arelocated in the appropriate data directories (e.g., DATA/LBDR/LBDR.FMT ).They describe the size, type, and meaning of each field. The LBDR.FMTand ABDR.FMT files reference the SBDR.FMT files for all fields held incommon by the three data sets.In order to further facilitate temporal segmentation of the data,the structure and time sequence of the data is described in thesequence design memo for the observation found in the EXTRAS directory.Each record in a BODP file is comprehensive and contains the acquisitiontime, viewing geometry, quality flags, and radar mode of the burst,so that data segmentation can be easily automated without resorting tothe sequence design memo.An SBDR record is produced for every burst throughout the pass in anobservation. An LBDR file is produced only for bursts during whichthe transmitter was on. (Sometimes it is necessary to create multipleLBDR files in order to avoid file lengths > 2 Gbytes which areproblematic for older operating systems.) An ABDR file is producedonly for periods in which the radar is in altimeter mode. If desired,bursts can be easily matched across data sets. One data field in eachrecord is a burst identifier, which uniquely distinguishes a burstfrom all other bursts in the mission. Records in different data setsthat correspond to the same burst have the same burst ID.The SBDR data record is divided into three consecutive segments fromthree different levels of processing: 1) the engineering data segment,2) the intermediate level data segment (mostly spacecraft geometry),and 3) the science data segment (brightness temperature, backscatter,measurement geometry, etc.). The engineering data segment contains acomplete copy of the telemetry data downlinked from the spacecraft.It includes temperatures, instrument instructions, operationalparameters of the radar, and raw measurements (i.e., unnormalizedradiometer counts.)For more information about the format and content of the SBDR, LBDR, andABDR files, see the Cassini Radar Burst Ordered Data Product (BODP)Software Interface Specification, JPL D-27891. A copy of the documentis located on this volume as file BODPSIS.PDF in the DOCUMENT directory.* ParametersA complete listing of the parameters can be found in the SIS.* ProcessingCassini RADAR telemetry packets are transmitted to earth along withother spacecraft and instrument telemetry at the conclusion of eachdata take. The radar data packets are queried from the telemetry datasystem (TDS) on a computer in the radar testbed which has access to TDS.These packets are placed sequentially into a raw data file. The raw fileis initially processed by radar software on the testbed computer whichidentifies radar science activity blocks (SAB) within the telemetry streamand reformats the data and provides some quick look displays and limitchecking.The reformatted data file (L0) is delivered to the radar processing groupfor processing by Radar Analysis Software (RAS) and then the SAR Processor(SP, if applicable). Temperature telemetry files from the spacecraftare also queried from TDS and delivered to the processing group for RASand SP to use. All other ancillary data is obtained from SPICE kernelfiles which are delivered by different elements of the project to an ftpsite. These files are separately archived in the PDS system. The RASpre-processor reads the radar L0 file, associated temperature telemetryfiles, and the SPICE kernel files and all relevant data are placed intothe SBDR/LBDR engineering and intermediate level data segments. Thescience processors for radiometery, scatterometry, and altimetry, as wellas SAR, ingest the SBDR/LBDR files and produce mode-specific science dataproducts (and modify science data segment fields).Note that measurement geometry will not be available and will be flaggedas invalid for cases in which there is no target body or the measurementextends beyond the limb of the target body. There is no plan to computethe science data segment for non-Titan bodies with the exception ofradiometric observations of Saturn and its rings. For other bodies thesefields will be flagged as invalid. For most non-Titan icy satelliteobservations, due to SNR effects, only a single brightness temperature orbackscatter measurement will be computable rather than values for eachburst. For these observations a single backscatter value and a singleantenna temperature value will be reported in the AAREADME.TXT file in theroot directory of the volume. Sometimes a short list of backscatter valueswill be reported as a function of frequency of the returned echo.* DataSee Parameters.* Ancillary DataThere are no ancillary data needed to use the LBDR.* Coordinate SystemData locations for each record are computed from Project SPICE kernels.Measurement geometry information is available for both the active andpassive mode measurements. Some of the active and passive mode quantitiesare likely to be identical (e.g., polarization orientation angle).However, separate data fields are reported, because the differences in thepassive and active mode measurement times can in principle cause the twocases to differ. Passive geometry is computed for the time correspondingto the midpoint of the passive receiver window (summed radiometer windows).Active mode geometry is computed for the time halfway between the midpointof the transmission and the midpoint of the active mode receiver window.The full set of measurement geometry for each case includes thepolarization orientation angle, emission/incidence angle, azimuth angle,the measurement centroid, and four points on the 3-dB gain contour of themeasurement. The centroid and contour points are specified in latitudeand longitude, using the standard west longitude positive geodetic(planetographic) coordinate system sanctioned by the IAU. The geodeticpart of the definition is moot since Titan is modeled by a sphere. Themeasurement geometry will not be available and will be flagged as invalidfor cases in which there is no target body or the measurement extendsbeyond the limb of the target body.* SoftwareNo software is provided within this volume.* Media/FormatThe data are provided on media as determined by PDS. The main datafiles are ZIPPED as described in the PDS standard. Detached labelsare provided for the ZIPPED files. The ZIPPED files also includetheir attached labels. Other formats are defined within the attachedlabels of the files.
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| DATA_SET_RELEASE_DATE |
2018-03-15T00:00:00.000Z
|
| START_TIME |
1999-08-18T03:37:24.327Z
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| STOP_TIME |
N/A (ongoing)
|
| MISSION_NAME |
CASSINI-HUYGENS
|
| MISSION_START_DATE |
1997-10-15T12:00:00.000Z
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| MISSION_STOP_DATE |
2017-09-15T12:00:00.000Z
|
| TARGET_NAME |
EARTH
DIONE
RHEA
TETHYS
ENCELADUS
HYPERION
IAPETUS
MIMAS
SUN
PHOEBE
TITAN
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| TARGET_TYPE |
PLANET
SATELLITE
SUN
|
| INSTRUMENT_HOST_ID |
CO
|
| INSTRUMENT_NAME |
RADAR
|
| INSTRUMENT_ID |
RADAR
|
| INSTRUMENT_TYPE |
RADAR
|
| NODE_NAME |
Imaging
|
| ARCHIVE_STATUS |
ARCHIVED - ACCUMULATING
|
| CONFIDENCE_LEVEL_NOTE |
* Confidence Level OverviewThe burst ordered data products (SBDR, LBDR, and ABDR) contain all sciencedata obtained by the Cassini RADAR instrument during the mission. A datarecord is obtained for each measurement cycle. This data is calibratedwhenever a calibrated value obtained from a single measurement cycle isphysically justified. This is always the case for close Titan flybys andseldom the case for other observations.* ReviewThe data will be validated internally by the Cassini Radar Team prior toeach release of data to the PDS. The overall data set organization willalso be peer reviewed once by the PDS prior to the release of the firstvolume.* Data Coverage and QualityThe following observations will be included in the SBDR and LBDR archives:1) Close (1000-200000 km) Titan flyby observations2) Distant Titan observations3) Observations of Saturn and its rings4) Observations of icy satellites5) Radiometer observation of Jupiter6) Sun scan observations used to calibrate antenna patterns7) Earth swingby observationThe SBDR contains one record for each active or passive measurement cyclebut does not contain the sampled radar echo data or altimeter profiles.The LBDR includes only active mode measurement cycles. It contains sampledradar echo data but no altimeter profiles.The ABDR includes only altimeter measurement cycles. It contains altimeterprofiles but no radar echo data.The ABDR-SUMMARY file is derived from the ABDR. It contains the estimatedsurface height and related measurements derived from the average of allpulses in a burst when the radar is in altimeter mode.SBDRs will be produced for all the observations mentioned above.LBDRs will be produced for close Titan flybys, the Earth swingby, and alsosome distant Titan and icy satellite observations whenever active modemeasurements are obtained.ABDRs and ABDR-SUMMARY files will only be produced for close Titan flybysbecause this is the only time altimeter mode is employed.Three types of calibrated measurements are obtained: backscatter(scatterometer), antenna temperature (radiometer), and surface height(altimeter).The calibrated scatterometer values are normalized radar cross-section, aunitless quantity related to the slope, roughness, and composition of theobserved surface. We currently estimate the accuracy of this quantity tobe + or - 3 dB absolute and + or - 2 dB relative. We estimate the accuracyof the antenna temperature to be + or - 5 percent absolute and + or - 0.2 Krelative.We estimate the accuracy of the surface height to be approximately + or -100-200 m.Location error of the measurements is dominated by ephemeris and pointingknowledge errors and is expected to be less than 2 km throughout themission.* LimitationsEphemeris error is expected to improve throughout the mission. Since thereis no plan to recompute the ephemeris of previous observations as newmeasurements are obtained, however, earlier observations may have poorerlocation accuracy.The dominant backscatter calibration error term is error in our knowledgeof the gain of the attenuators in the receiver. Engineering tests arecurrently planned to improve our knowledge of the attenuator gains.Besides ephemeris error, the main errors in the altimeter surface heightdetermination come from off-nadir pointing and actual surface heightvariation with the altimeter footprint of diameter typically 25-50 km.
|
| CITATION_DESCRIPTION |
N/A
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| ABSTRACT_TEXT |
N/A
|
| PRODUCER_FULL_NAME |
Philip S. Callahan
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| SEARCH/ACCESS DATA |
Imaging Online Data Volumes
Imaging Planetary Image Atlas
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