Cassini Radar Burst Ordered Data Products SIS
Table of Contents
1 INTRODUCTION .................................................................................................................... 1
1.1 Purpose and Scope ........................................................................................................... 1
1.2 Applicable Documents (References) .................................................................................. 1
1.3 Relationships with Other Interfaces ................................................................................... 2
2 DATA PRODUCT CHARACTERISTICS AND ENVIRONMENT ........................................... 2
2.1 Instrument Overview ......................................................................................................... PAGEREF _Toc202179734 \h 2
2.2 Instrument Description Summary ...................................................................................... 3
2.3 Data Products Description ................................................................................................. 3
2.3.1 Engineering Data Segment ......................................................................................... 5
2.3.2 Intermediate Level Data Segment ................................................................................ 6
2.3.3 Science Data Segment ............................................................................................. 10
2.3.4 Sampled Echo Data ................................................................................................. 15
2.3.5 Altimeter Profile ....................................................................................................... 15
2.4 Data Processing ............................................................................................................... 16
2.4.1 Data Product Generation ........................................................................................... 16
2.4.2 Science Processing and Calibration Algorithms .......................................................... 16
2.4.3 Data Flow ................................................................................................................ 16
2.4.4 Labeling and Identification ......................................................................................... 17
2.5 Standards Used in Generating Data Products .................................................................. 19
2.5.1 Coordinate Systems ................................................................................................. 19
2.5.2 PDS Standards ........................................................................................................ 19
2.5.3 Data Storage Conventions ......................................................................................... 20
2.6 Data Validation ................................................................................................................ 20
3 Applicable PDS Software Tools ............................................................................ 20
4 Appendix A Example LBDR PDS Label ...................................................................... 21
5 Appendix B.1: Partial Contents of SBDR.FMT .................................................... 23
6 Appendix B.2: Contents of LBDR.FMT .................................................................... 24
7 Appendix: B.3 Contents of ABDR.FMT .................................................................... 24
8 Appendix C: Detailed Description of Fields in SBDR record ................... 25
8.1 SBDR Start Byte Table ..................................................................................................... 25
8.2 List of SBDR Field Descriptions ....................................................................................... 32
8.2.1 Engineering Data Segment Fields .............................................................................. 32
8.2.2 Intermediate Level Data Segment Fields ..................................................................... 65
8.2.3 Science Data Segment Fields ................................................................................... 77
9 Appendix D: ABDR Summary File (ASCII CSV) ......................................................... 89
The purpose of this Data Product Software Interface Specification (SIS) is to provide users of the Cassini Burst Ordered Data Products (BODP) with a detailed description of the products and a description of how they were generated. Cassini Burst Ordered Data Products are data sets at various stages of processing which are organized as time-ordered records for each burst. The products described in this SIS are listed in Table 1, Cassini Burst Order Data Products.
Table 1: Cassini Radar Burst Ordered Data Products
This SIS is intended to provide enough information to enable users to read and understand the Cassini Burst Ordered Data Products. This SIS is intended for software developers, engineers, and scientists interested in accessing and using these products.
This Data Product SIS describes how Cassini Radar Burst Ordered Data Products were processed, formatted, labeled, and uniquely identified. The document discusses standards used in generating the product and software that may be used to access the product. The data product structure and organization is described in sufficient detail to enable a user to read the product.
A description of the BODP product formats and the data contained in them is provided in Section 2.3 -- Data Products Description. This description is at a level of detail, which we expect to be useful for the majority of users. For examples of PDS labels (headers) see Appendices A and B. For a detailed description of all the data fields in the BODP products and a table of their locations in the file see Appendix C. The length of records can also be found in Appendix C as well as in the attached PDS label of each BODP file.
This Data Product SIS is responsive to the following Cassini documents:
1) Project Data Management Plan, JPL D-12560, PD 699-061, Rev. B, April 1999, and Science Management Plan, JPL D-9178, PD 699-006, July 1999.
2) Cassini RADAR Basic Image Data Records SIS, JPL D-27889, Feb 2004, Version 1.0.
3) Cassini/Huygens Archive Plan for Science Data, JPL D-15976, 699-068.
4) SIS for Cassini RADAR Digital Map Products, JPL D-xxxx, Version 1.0
This SIS is also consistent with the following Planetary Data System documents:
5) Planetary Data System Data Preparation Workbook, Version 3.1, February 17, 1995, JPL D‑7669, Part 1.
6) Planetary Data System Data Standards Reference, June 15, 2001, Version 3.4, JPL D‑7669, Part 2.
7) SIS for Cassini Radar Basic Image Data Records, JPL Document #D-27889
8) Volume SIS for Cassini Radar Digital Map Products, JPL Document #D-30412, USGS #IO‑AR‑014
9) SIS for Cassini Radar Digital Map Products, JPL Document #D-30411, USGS #IO‑AR‑015
10) Volume SIS for Cassini Radar Instrument Team Data Products, Document # D-27890
Finally, this SIS is meant to be consistent with the contract negotiated between the Cassini Project and the Cassini RADAR Experiment Principal Investigator (PI) in which data products and documentation are explicitly defined as deliverable products.
There are two other data product sets that contain data from the Cassini Radar instrument. These are:
the Basic Image Data Records (BIDR) and
the Digital Map Products (DMP).
Both of these product sets are downstream from the data products described in this document. The Cassini Radar Instrument team is responsible for developing and documenting the BIDR data. See SIS [7].
The document that describes the volume which contains BODP and BIDR data is [10].
Randolph Kirk of the US Geological Survey is responsible for developing and documenting the DMP data. The relevant SIS's are [8] and [9].
The Cassini RADAR is a facility instrument on the Cassini Orbiter. It is capable of passive (radiometer) and active (scatterometer, altimeter, SAR imaging) operation. During active mode operation interleaved passive measurements are also obtained.
The primary target for Cassini Radar observations is Titan, the largest Saturnian moon. Due to its thick hazy atmosphere, Titan's surface was not imaged successfully by the Pioneer or Voyager spacecraft, though atmospheric "windows" in the near infrared have been exploited by the Hubble Space Telescope and earth-based telescopes to produce low-resolution albedo maps of part of the surface. The Cassini radar instrument will obtain backscatter and altimeter sounding measurements of portions of Titan's surface. High resolution synthetic aperture radar (SAR) backscatter images of 15% of Titan's surface will be obtained. Radiometer measurements covering the entire surface of Titan will also be acquired.
Imaging (13.78 GHz; 0.425 MHz & 0.85 MHz bandwidth)
Altimeter (13.78 GHz; 4.25 MHz bandwidth)
Scatterometer (13.78 GHz; 0.1 MHz bandwidth)
Radiometer (13.78 GHz; 135 MHz bandwidth)
Number of nominal Operational Periods:
One (1) per selected flyby of Titan (approximately 12 to 22 flybys, total)
Duration of nominal Operational Period:
From 300 minutes before to 300 minutes after closest approach to Titan for prime operation.
30 kbps: Altimeter & Scatterometer / Radiometer
365 kbps: SAR Imaging / Radiometer
This document describes the data included in the Burst Ordered Data Products. Burst Ordered Data Products (BODP) are comprehensive data files that include engineering telemetry, radar operational parameters, raw echo data, instrument viewing geometry, and calibrated science data. The BODP files contain time-ordered fixed length records. Each record corresponds to the full set of relevant data for an individual radar burst. The Cassini Radar is operated in "burst mode", which means the radar transmits a number of pulses in sequence then waits to receive the return signals. "Burst" is a descriptive term for the train of pulses transmitted by the radar. We use the term "burst" (somewhat unconventionally) to refer to an entire measurement cycle including transmit, receipt of echo, and radiometric (passive) measurements of the naturally occurring radiation emitted from the surface. In fact, even when the transmitter is turned off and only passive measurements are made we still refer to the measurement cycle as a burst.
Burst Ordered Data Products are fixed header length, fixed record length files. The header is an attached PDS label. See Section 2.4.4 -- Labeling and Identification for a description of BODP attached PDS labels and Appendix A and B for examples. Records are rows in a table. Each data field is a column. All one needs to know to read a particular data value from a particular data field is the header length, the record size, and the byte offset of the data field within the record. Since a UTC time tag is included in each record, it is a simple matter to restrict the data one reads to a particular time interval. In order to further facilitate temporal segmentation of the data, we plan to provide a Cassini Radar Transition (CRT) file for each Titan pass. This file will maintain a temporally ordered list of the times and transition types for all scan start and end events, and radar mode transitions (e.g., radiometry to scatterometry mode switch). See the Volume SIS for more information about CRT file formats.
The BODP comprise three separate similar data sets, including the Short Burst Data Record (SBDR) the Long Burst Data Record (LBDR) and the Altimeter Burst Data Record (ABDR) plus the ABDR Summary file. The only difference among the first three formats is whether or not two data fields are included: the sampled echo data, and the altimeter profile. The altimeter profile is an intermediate processing result between sampled echo data and a final surface height estimate. LBDRs include the echo data but not the altimeter profile. ABDRs include the altimeter profile but not the echo data. SBDRs include neither. Note that the ABDR and ABDR Summary files only cover time periods when the instrument is in altimetry mode (e.g., bandwidth). These trivial differences necessitate different data sets because the two fields in question are much larger than all the other data fields combined. The majority of the bursts in a typical Titan pass are passive measurements. These bursts do not produce echo data or altimeter profiles. Of the active mode bursts most are not in altimeter mode so no altimeter profiles are produced. Including these two data fields when they are invalid would ridiculously increase the size of the archived data. The alternative of having variable length records was deemed to overly complicate data archiving and analysis procedures. Maintaining three data sets reduces data volume while allowing record lengths to remain fixed. The ABDR Summary file is an ASCII comma-separated value file that provides additional information derived from the altimeter profile. The ABDR Summary file is an addition to Version 2 of the data and is described in Appendix D.
Consider a typical Titan pass. When approaching Titan, first only radiometer measurements are obtained. Then the transmitter is turned on and scatterometer measurements are added. When Titan is close enough for useful altimetry, the radar goes into altimeter mode. Finally, about 15 minutes prior to closest approach SAR observation begins. On the outbound portion of the pass these transitions occur in reverse. When the data from a pass is received on the ground, it is processed in the following manner: An SBDR record is produced for every burst throughout the pass. An LBDR file is produced which only contains records for the middle portion of the pass during which the transmitter was on. (Sometimes it is necessary to create multiple LBDR files in order to avoid file lengths > 2Gbytes which are problematic for older operating systems.) An ABDR file is produced which contains records for only the periods (typically one inbound, one outbound) in which the radar is in altimeter mode. If desired, bursts can be easily matched across data sets. One data field in each record is a burst identifier, which uniquely distinguishes a burst from all other bursts in the mission. Records in different data sets that correspond to the same burst have the same burst ID.
Excepting unitless quantities and raw telemetry, all data fields are stored in standard units:
9 velocity in kilometers per second
10 angular velocity in degrees per second
The SBDR data record is divided into three consecutive segments from three different levels of processing: 1) the engineering data segment, 2) the intermediate level data segment (mostly spacecraft geometry), and 3) the science data segment (antenna temperature, backscatter, measurement geometry, etc.). Below, in Sections 2.3.1 -- 2.3.3, we describe a subset of the fields in each of these data segments which is likely to be of interest to the average user. The engineering data segment contains a complete copy of the telemetry data downlinked from the spacecraft and thus has the most fields by far. It includes temperatures, instrument instructions, operational parameters of the radar, and raw measurements (i.e., unnormalized radiometer counts.) For the sake of conciseness, we avoid discussing many of these fields here. For a full description of all SBDR fields see Appendix C. In Section 2.3.4 we describe the raw active mode data, and in Section 2.3.5 we describe the altimeter profile.
The engineering data segment includes a copy of the radar telemetry contained in the Engineering Ground Support Equipment (EGSE) files obtained from the spacecraft data downlinks. This data is stored to allow investigators to access as much of the information obtained by the spacecraft as possible. Telemetry data is decoded and converted to standard units. The most important fields in this segment are the radar operational parameters and the raw radiometer data. The following table documents each of these fields. Each field in the table is 4 bytes long.
Table 2: Fields of Interest in the Engineering Data Segment
|
An integer which uniquely identifies each burst throughout the mission. |
||
|
The receive window length in units of PRI (pulse repetition interval). |
||
|
The operational mode of the radar. 0 = Scatterometry, 1 = Altimetry, 2 = Low resolution SAR, 3 = High resolution SAR, 4 = Radiometer only. Adding 8 to any of these values indicates auto-gain is enabled. Auto-gain is N/A for Radiometer only mode. |
||
|
Analog to Digital Converter sampling rate in Hz. This is the rate at which the echo is sampled. Since Cassini uses video offset rather than IQ sampling. Each sample is a real (not complex) value. |
||
|
The length of a single radiometer antenna measurement window in seconds. |
||
|
Number of chirp steps. One step means two different frequencies before and after the step, so that the number of distinct frequencies is one more than the number of steps. |
||
|
Total length of chirp in seconds. This is equivalent to the width (during transmission) of an individual pulse. |
||
|
Time in seconds from start of burst to start of receive window. |
||
|
Radiometer antenna measurement summed over all windows (raw counts). |
||
|
The length of the noise diode measurement window in seconds. |
||
|
The length of the resistive load measurement window in seconds. |
||
|
A flag which identifies the method used to compress the raw active mode data. Usually this value is unimportant to the user because the echo data has been decompressed. When the value is 3, however, the raw echo data has a special meaning. See below. |
||
|
Number of bursts transmitted with a single round trip time. The value is almost always 1. In this case, all the fields in the record correspond to the same measurement. For more details, see num_bursts_in_flight . |
||
|
Number of valid data values in the time sampled echo data array after decompression. |
||
|
Root mean square of the time sampled echo data after decompression. |
The Intermediate Level Data Segment contains timing and spacecraft geometry information which is computed using various NAIF kernel files in addition to the EGSE raw radar telemetry file. It also contains several temperatures which were obtained from ancillary spacecraft temperature telemetry files.
The SPICE geometry library is used to compute spacecraft ephemeris and attitude information in two coordinate frames: an inertial frame (J2000) centered on the target (typically Titan), and the target body fixed frame (TBF). Although both frames are centered on the target, the orientations of the frames differ. The TBF frame maintains a constant orientation with respect to any point on the surface of the target. For example, if the target were Earth, the TBF coordinates of the point 100 m above the Washington monument would not change with time. The inertial frame coordinate system is the standard J2000 coordinate system translated so that it is centered at the target's (Titan's) center at the time of the start of the burst.
For observations of other icy satellites, Jupiter, Saturn, Earth, or Venus, the target will be the body in question, and the J2000 and TBF coordinate systems will be defined accordingly. (Ring observations will have the target "RINGS" but the TBF coordinate system will be IAU_SATURN, the official IAU Saturn body fixed coordinate system.) Some observations will be distant microwave sources or cold sky calibration. For these cases the s/c geometry will be Earth centered for J2000, and the TBF fields will have special meaning. TBF fields for cold sky calibrations are invalid. For microwave source scans, TBF spacecraft position is a unit vector pointing from the spacecraft to the microwave source, spacecraft velocity is 0, and all other TBF parameters default to J2000 values. Microwave source scans are readily identified because the target_name field contains a string designating the microwave source (i.e. ORION, M15, etc) rather than a solar system body. Text (character string) fields for the name of the target and the official name of the target body fixed coordinate frame are reported for each burst.
The data fields in this segment include time at start of burst, spacecraft position and velocity, the direction vectors of the axes of the spacecraft coordinate system, and the angular velocity vector of the spacecraft.
The spacecraft position and velocity vectors are obtained at the start time of the burst (t_ephem_time). The geometry for active mode data is calculated at
t_ephem_time + act_geom_time_offset.
act_geom_time_offset is midway between the center of the transmit window and the center of the receive window -- the average time that the signal was reflected from the surface.
The geometry for passive mode data is calculated at
t_ephem_time + pass_geom_time_offset.
pass_geom_time_offset is the mid-point of the summed radiometer windows.
Users can compute the spacecraft position at either of these times using values of the position and velocity in an equation shown generically as
new_sc_pos = sc_pos + geom._time_offset * sc_vel
where sc_pos and sc_vel are in the desired coordinate system, the time offset is active or passive, and the equation applies to each component of the position. Performing this position update is crucial to using the altimeter data in the ABDR.
The following table documents each field in detail. Geometry information is often expressed as three dimensional vectors. Such information is stored as three data fields: one for each of the x, y, and z components. In the table only the x components are listed. X-component data field names end in "_x" (e.g., sc_vel_j2000_x), y-component field names in "_y", and z-component field names in "_z". The three components are always consecutive in x, y, z order. Fields with data type "double" are real valued 8 byte numbers. UTC time strings are 24 bytes long. Other strings are multiples of 4 bytes long as specified in the table. All other fields are four bytes long.
Table 3: Fields of Interest in the Intermediate Level Data Segment
Two primary estimates of geophysical quantities are available in the science data segment: 1) the normalized backscatter cross-section σ 0 obtained from the scatterometer measurement, 2) the antenna temperature determined from the radiometer measurement. The antenna temperature is computed for every burst. The normalized backscatter cross-section is computed for all bursts with active mode data. For each burst in altimeter mode, the surface height is estimated. In addition to these primary values, ancillary parameters are also computed. The ancillary parameters include intermediate values (e.g., receiver temperature, total echo energy, system gain, etc.), analytical estimates of the standard deviation of the residual error in each of the two primary measurements, and measurement geometry. A "corrected" version of σ 0 is also computed in which the effects of incidence angle are removed by a global average model. This quantity is produced in order to ease the identification of surface features from σ 0 maps. Science team input was used to specify the incidence angle correction method. Synthetic Aperture Radar (SAR) ancillary data is also included in the science data segment when available. The SAR images themselves are stored in the Basic Image Data Record (BIDR) files.
Measurement geometry information is available for both the active and passive mode measurements. Some of the active and passive mode quantities are likely to be identical (e.g. polarization orientation angle). However, separate data fields are reported, because the differences in the passive and active mode measurement times can in principle cause the two cases to differ. Passive geometry is computed for the time corresponding to the midpoint of the passive receiver window (summed radiometer windows). Active mode geometry is computed for the time halfway between the midpoint of the transmission and the midpoint of the active mode receiver window. The full set of measurement geometry for each case includes: the polarization orientation angle, emission/incidence angle, azimuth angle, the measurement centroid, and four points on the 3 dB gain contour of the measurement. The centroid and contour points are specified in latitude and longitude, using the standard west longitude positive geodetic coordinate system sanctioned by the IAU. The geodetic part of the definition is moot since Titan is modeled by a sphere. See [1] and [3] for a more rigorous definition of the coordinate system. The measurement geometry will not be available and will be flagged as invalid for cases in which there is no target body or the measurement extends beyond the limb of the target body. There is no plan to compute the science data segment for non-Titan bodies with the exception of radiometric observations of Saturn and its rings. For other bodies these fields will be flagged as invalid. For most non-Titan icy satellite observations, due to SNR effects, only a single antenna temperature or backscatter measurement will be computable rather than values for each burst. For these observations a single backscatter value and a single antenna temperature value will be reported in the AAREADME.TXT file in the root directory of the volume. (No altimetry data will be obtained for bodies other than Titan.)
The following table summarizes the data fields in the science data segment. All fields are 4 bytes long except doubles which are 8 bytes. When a field is invalid its value is set to zero and the science_qual_flag bits are set accordingly.
Table 4: Science Data Segment Data Fields
The sampled echo data array is located at the end of each record in the LBDR data files. It constitutes the only difference between SBDR records and LBDR records. The array consists of 32, 768 4-byte floating-point values. It contains the active mode time-sampled data obtained during the receive window. The data was encoded prior to downlinking from the spacecraft in order to minimize the data transfer rate, and then decoded during the ground processing (the data stored in the array has already been decoded). The length of the array corresponds to the maximum amount of echo data that can ever be obtained from a single burst. Only the first N elements in the array are valid data. These data are N floating point values in the range [-127.5, 127.5] sampled consecutively at a rate of B Hz. N is stored in the raw_active_mode_length data field in the engineering data segment. B is in the adc_rate field in the same segment. The raw_active_mode_rms field (also in the engineering data segment) contains the root mean square of the N sampled echo data values. We suspect that only a few investigators will actually need to make use of the sampled echo data.
There is one special case in which the sampled echo data takes on a different meaning. When the baq_mode field is set to 3 that signifies the compressed scatterometer mode. In this mode all data samples are not downlinked from the spacecraft. Instead, the absolute values of the samples are summed across all the pulses in the pulse train. The summation is stored in the sampled echo data array. (Since it is a summation, the values may be outside the nominal range.) In this case an additional data value is appended after the N=raw_active_mode_length array. The (N+1)st sample corresponds to the DC offset of the entire pulse train.
The altimeter profile is an intermediate result in the altimeter processing. The altimeter profile is the range compressed active mode data obtained while the radar is in altimeter mode (bandwidth). It is located at the end of each record in the ABDR files. It is an array of floating point values with the number of values stored in the altimeter_profile_length data field in the science data segment. During range compression the active mode data is segmented by pulse. Each pulse is correlated with a real -valued replica of the chirped transmit waveform in order to distribute the energy within each returned pulse into range bins. The range for the first sample of the altimeter profile and the range step are data fields in the science data segment. The number of pulses received is also stored in the science data segment. Dividing the profile length by the number of pulses yields the number of range bins. The profile array is arranged so that the range bins for each pulse are contiguous in the array (i.e., (Pulse1, Range1), (Pulse1, Range2) ..., (Pulse1, Range n), (Pulse2, Range1), (Pulse2, Range2), ...).
During the development of the altimeter processor it was found that the altimeter signal was rather complex and had unique characteristics that were not well-represented by just the two values in the SBDR portion of the record. It was decided to partially analyze the data into a stand-alone data product that could be used by more people than might be willing to use the altimeter profiles. This additional ABDR Summary file is described in Appendix D.
This document uses the "Committee of Data Management and Computation" (CODMAC) data level number system. The data products referred to in this document are "level 3."
The JPL Cassini RADAR science data products will be produced by the radar processing group in Section 334. The pre-processor (part of the radar analysis software (RAS)) creates SBDR and LBDR files for each radar observation (i.e., each Titan pass). Initially these files only contain valid data in the engineering and intermediate level data segments. These files will then be used as inputs for the various science processing (SP) routines. Processors for the radiometer and scatterometer are applied to the SBDR and LBDR files. The scatterometer processor puts data into the scatterometer fields in the science data segment. The radiometer processor fills the radiometer data fields. The altimeter processor will generate an ABDR file (only for altimeter mode data) and populate the altimeter data fields in the BODP files. The SAR processor will produce a Basic Image Data Record file containing a SAR image and populate the SAR ancillary data fields in the BODP files. These programs will also apply low level (instrument based) calibration to the resulting data records, but will generally not attempt to perform data-driven calibration techniques. In some cases, the calibration model will be produced by other RAS software and communicated via configuration file. Configuration files will be archived along with the data. RAS and SP software will ingest telemetry data and other ancillary data (NAIF SPICE files) which are separately archived by other elements of the Cassini project.
When the development of the radiometer, scatterometer, SAR, and altimeter processors is complete, each of these algorithms will be summarized here. References to peer-reviewed articles will be provided when available to further document the algorithms employed along with the calibration methods contained in those algorithms.
Cassini RADAR telemetry packets are transmitted to earth along with other spacecraft and instrument telemetry at the conclusion of each data take. The radar data packets are queried from the telemetry data system (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 file is initially processed by radar software on the testbed computer which identifies radar science activity blocks (SAB) within the telemetry stream and reformats the data and provides some quick look displays and limit checking. The reformatted data file (L0) is then delivered to the radar processing group for processing by RAS and then SP. Temperature telemetry files from the spacecraft are also queried from TDS and delivered to the processing group for RAS and SP to use. All other ancillary data is obtained from SPICE kernel files which are delivered by different elements of the project to an ftp site. These files are separately archived into the PDS system.
The RAS pre-processor reads the radar L0 file, associated temperature telemetry files, and the SPICE kernel files; and all relevant data are placed into the SBDR/LBDR engineering and intermediate data segments. The science processors ingest the SBDR/LBDR files and produce mode specific science data products and modify science data segment fields. These products will be delivered to PDS and to the mapping group at the United State Geological Survey (USGS) in Flagstaff AZ. There, the data products will be processed into higher level map products documented in the DMP SIS. During the primary mission (July 2004 through July 2008) approximately 18 Titan flybys will have radar data takes. In addition, various radar observations will be conducted on other icy satellites, the rings, and Saturn's atmosphere. The processing chain will be operated about once per month to produce the relevant science data products for each data take.
The data products discussed in this SIS all have attached PDS labels. For a general description of PDS labels and for the file naming conventions for this data set see the Volume SIS.
A PDS label is object-oriented and describes the objects in the data file. The PDS label contains keywords for product identification, and storing and organizing ancillary data. The label also contains descriptive information needed to interpret or process the data objects in the file.
PDS labels are written in Object Description Language (ODL) [ref. 5]. PDS label statements have the form of "keyword = value". Each label statement is terminated with a carriage return character (ASCII 13) and a line feed character (ASCII 10) sequence to allow the label to be read by many operating systems. Pointer statements with the following format are used to indicate the location of data objects in the file:
where the carat character (^, also called a pointer) is followed by the name of the specific data object. The location is the starting record number for the data object within the file. The keywords used are listed in the following table. The text following the description keyword includes several UTC times of interest in day of year (doy) format including the closest approach time of the pass, the trigger time of the radar instrument command sequence, and the epoch time (usually the same as the closest approach time). See Appendices A and B for example PDS labels.
Geometrical data such as spacecraft position, velocity and attitude, are reported in the inertial target-centered J2000 coordinate frame as well as in a target body fixed (TBF) rotating frame. Measurement locations are reported in the TBF frame as planetodetic surface coordinates (latitude and longitude). The PDS Navigation and Ancillary Information Facility (NAIF) definitions are used for the frames. The TBF frame for each target is defined in the NAIF planetary kernel file (PCK) for the Saturnian system. This file will be updated during tour as Cassini observations improve knowledge of the states of bodies in the Saturnian system. In particular, the spin state of Titan has been updated based on an initial analysis of the Radar images (B.W. Stiles et al, 2008, "Determining Titan's Spin State from Cassini Radar Images", Astron. Journal , 135 , 1669). In order to fully document the coordinates used, the PCK file used in the processing is included in the EXTRAS directory. A s of this writing, the solution from Stiles et al is being used for data takes Ta through T30 for which it was fit, while a simpler long-term solution from NAIF is used for data takes after T30.
For convenience, the set of angles used to transform coordinates from the inertial frame to the target body fixed (TBF) frame is also included in the BODP files (see Intermediate Data Segment, e.g., pole_right_ascension, pole_declination, target_rotation_rate, target_rotation_angle).
The Cassini Burst Ordered Data Products comply with the Planetary Data System standards for file formats and labels, as specified in the PDS Standards Reference [4].
The Cassini Burst Ordered Data Products contain binary data. Data is stored as 32 bit integers, 32-bit IEEE floating point, or 64-bit IEEE floating point as appropriate. The files are generated on a PC running the Linux operating system so little endian byte ordering is employed. The PDS label sections are stored as ASCII character strings conforming to the conventions outlined in the PDS Standards Reference [4].
Cassini Radar Burst Ordered Data products will be validated before being released to the PDS. Validation is accomplished in two parts: validation for scientific integrity and validation for compliance with PDS standards. The Cassini Science Archive Working Group (SAWG) Data Validation Team will oversee validation, which includes representatives from Radar Team and PDS. Science team members are expected to conduct validation for scientific integrity in the course of their analysis of the products. The details of the science validation process are the responsibility of the Radar Science Team.
Validation for compliance with PDS standards is also the responsibility of the Radar Science Team with help from the PDS Imaging Node that will receive the data products. PDS will provide software tools, examples, and advice to help make this part of the validation as efficient as possible.
A data set will pass a peer review before it is accepted by PDS. The Cassini Radar Team and the associated PDS Node will convene a peer review committee made up of scientists and data engineers. The committee will examine the data set to make sure it is complete, meets the product specifications as defined in the SIS. The committee will include a PDS representative to ensure that the data set is in compliance with PDS standards.
PDS-labeled tables can be viewed with the program NASAView developed by the PDS and available for a variety of computer platforms from the PDS web site at
http://pdsproto.jpl.nasa.gov/Distribution/license.html
There is no charge for NASAView.
/* POINTERS TO START RECORDS OF OBJECTS IN FILE */
DATA_SET_ID = "CO-V/E/J/S-RADAR-3-LBDR-V1.0"
DATA_SET_NAME = "CASSINI ORBITER RADAR LONG BURST DATA RECORD"
PRODUCER_INSTITUTION_NAME = "JPL CAL TECH"
PRODUCER_FULL_NAME = "INST LEAD CHARLES ELACHI CONTACT BRYAN STILES"
INSTRUMENT_HOST_NAME = "CASSINI ORBITER"
INSTRUMENT_NAME = "CASSINI RADAR"
START_TIME = YYYY-DOYThh:mm:ss
SPACECRAFT_CLOCK_START_COUNT = nnnnnnnnn
SPACECRAFT_CLOCK_STOP_COUNT = nnnnnnnnn
PRODUCT_CREATION_TIME = YYYY-DOYThh:mm:ss.sss
MISSION_NAME = "CASSINI-HUYGENS"
SOFTWARE_VERSION_ID = "V1.0"
DESCRIPTION = "CASSINI RADAR LONG BURST DATA RECORD FOR THE TA TITAN PASS WITH CLOSEST APPROACH TIME YYYY-DOYThh:mm:ss.sss TRIGGER TIME YYYY-DOYThh:mm:ss.sss and EPOCH TIME YYYY-DOYThh:mm:ss.sss."
PROCESSING_HISTORY_TEXT="....."
/* DESCRIPTIONS OF OBJECTS CONTAINED IN FILE */
DESCRIPTION = "This is the table definition for a Cassini Radar Long Burst Data Record, which includes a Short Burst Data Record (engineering telemetry, spacecraft geometry, and calibrated science data) plus the raw counts of the sampled echo data."
OBJECT = COLUMN
DATA_TYPE = PC_UNSIGNED_INTEGER
UNIT = "NO UNIT OF MEASUREMENT DEFINED"
DATA_TYPE = PC_UNSIGNED_INTEGER
DATA_TYPE = PC_UNSIGNED_INTEGER
UNIT = "NO UNIT OF MEASUREMENT DEFINED"
.(..... Continues for 235 columns totaling 1272 bytes.)
DESCRIPTION = "Array of 32, 768 real samples of the RADAR echo return. Each real value is an antenna voltage estimate at a particular instant in time. These estimates are proportional to voltage but are expressed in data numbers and need to be converted to engineering units. The values may or may not have passed through a lossy BAQ compression/decompression algorithm. The timing of the samples and other relevant RADAR instrument parameters are included in the engineering data segment of each LBDR record."
DESCRIPTION = "Array of 32, 768 values resulting from range compression of the sampled echo data counts obtained while in altimeter mode. Detailed description pending altimeter processor development."
The following table lists the starting byte of each field in a SBDR record along with long and short names for each field and its length in bytes. The long names are the names used to document the field and the names employed in the PDS format file `SBDR.FMT' (See Appendix B). The short names are values occurring in the ground processing software and are included here to assist the software developers. An SBDR record is 1272 bytes long.
Data items below are numbered 8.2.n.#, where n = 1, 2, 3 for Engineering, Intermediate, Science Data Segments in order to keep a running count of the items.
Constant hexadecimal value used for binary format checking.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 77746B6A hexadecimal
maximum_value: 77746B6A hexadecimal
Reference spacecraft clock count for each burst. The LSB is nearly 1 second but not exactly. For exact time references use t_ephem_time
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: 1 spacecraft clock count
minimum_value: 0
maximum_value: 2 32 -1
An identifier for each burst which is unique for the course of the mission.
Consecutive bursts within a data take have consecutive record_id values.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 2 32 -1
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: bits/s
valid_values: 364800, or 30400
Burst start time expressed as an offset from the reference spacecraft clock count.
The precise spacecraft time at the start of the burst is sclk + brst in seconds.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: s
minimum_value: 0.0
Specified execute time of test and control instruction expressed as time after IEB trigger, bits 0-15 of Test and Control IEB instruction.
PDS_Object: Column of Table
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
minimum_value: 0
maximum_value: 65535 (18.2 hours)
Test and control mode, bits 24-31 of Test and Control IEB.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
Instruction type (test and control), bits 22-23 of Test and Control IEB.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
possible value: 1
Test and Control Parameter A, bits32-47 of Test and Control IEB
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
Test and Control Parameter B, bits 48-63 of Test and Control IEB
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
Test and Control Parameter C, bits 64-79 of Test and Control IEB
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
Most recent power instruction.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 2 32 -1
Valid/invalid spacecraft command count (least significant 16 bits). Bit 0 (MSB) 0=valid, 1=invalid. Bits 1-15 represent command counter.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
Valid/invalid spacecraft message count (least significant 16 bits). Bit 0 (MSB) 0=valid, 1=invalid. Bits 1-15 represent message counter.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
Word (16-bit) count of SAR/ Altimeter Block (SAB) tail.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
possible values: 0 (no tail), 32, 16384
Running count of non-zero length SAB tails.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
Word (16-bit) count of SAB data field.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
Flight software error module ID.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
Count down for bursts in instruction.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
This field is 11 bits read from the 16 bit DCREG register in the CTU: the format of this field is:
L, P/SLKD, P/SLKD, HPALKD, HPALKD, C, B, A, C, B, A
(L = DCREG[15] = DCREG MSB = CTPS MSB)
In terms of DCREG bits the CTPS format is: DCREG[15, 14, 13, 10, 9, 8, 7, 6, 5, 4, 3]
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 2047
Current beam number in unitary code, e.g. 100002 = beam 5 enabled.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
possible values: 100002, 010002, 001002, 000102, 000012
Original telemetry 16 bit encoding of CTPS (Most significant 11 bits) and CTBE (least significant 5 bits) stored as a 32 bit integer.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 64094
Instruction read back disagree (IRBD) which consists of 17 single bit flags at the end of a SAB header.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
maximum_value: 2 17 - 1
Time from IEB trigger for slow field instruction.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535 (18.2 hours)
Definition: 000000002 = the first IEB Sequence Table uploaded after launch.
The MOS will increment this parameter by one for every new IEB Sequence Table that is uploaded. This value will "roll over" from 255 to 0 if necessary.
Typical events that will cause the generation and uploading of a new IEB Sequence Table include:
Normal Radar SAR or ALT operation at Titan
Calibration not associated with normal operation (e.g. period Cruise Phase calibration)
Icy satellite measurements, imaging
"Target-of-opportunity" measurements, imaging
PDS_Object: Column of Table
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
Slow field instruction type (3).
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
possible value: 3
The following bit patterns are assigned to the various Calibration Sources: (the three or four character mode name is in parenthesis)
00002 = Normal Operation. (norm)
00012 = Antenna being used as the Calibration Source. (ant)
00102 = Noise Diode being used as the Calibration Source. (diod)
00112 = Resistive Load being used as the Calibration Source. (load)
01002 = Rerouted Chirp being used as the Calibration Source. (chrp)
01012 = Leakage Signal being used as the Calibration Source. (leak)
01102 = Radiometer Only Calibration Mode. (rado)
01112 = Transmit Only Calibration Mode. (xmto)
10002 = Auto-Gain Control. (agc)
10012 - 11112 = (reserved by the CTU)
PDS_Object: Column of Table
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 15
This field represents the radar mode, and is defined as follows:
(the four character mode name is in parenthesis)
00002 = ALTL: Altimeter, Low-Resolution (altl)
00012 = ALTH: Altimeter, High-Resolution (alth)
00102 = SARL: Synthetic Aperture Radar, Low-Resolution (sarl)
00112 = SARH: Synthetic Aperture Radar, High-Resolution (sarh)
01002 = Radiometer Only (rado)
01012 = Inter-Galactic Object ( IGO) Calibration (igoc)
01102 = Earth Viewing Calibration (evca)
01112 = Bi-Static Operation (bsop)
10002 = ALTL with Auto Gain (alag)
10012 = ALTH with Auto Gain (ahag)
10102 = SARL with Auto Gain (slag)
10112 = SARH with Auto Gain (shag)
PDS_Object: Column of Table
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 15
Slow field instruction number. The MOS will reset this parameter to zero (000000002) for every Data Take, and will increment this parameter by one for every slow field instruction. This value will "roll over" from 255 to 0 if necessary.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
The following bit patterns describe the possible Beam Masks used by the Cassini RADAR DSS:
000002 = All beams disabled (Used during internal source Calibration modes such as noise diode, resistive load and rerouted chirp).
000012 = Beam #1 Only enabled.
000102 = Beam #2 Only enabled.
000112 = Beams #2 and #1 enabled.
100002 = Beam #5 Only enabled.
110102 = Beams #5, #4 and #2 enabled.
111112 = All Five Beams enabled.
PDS_Object: Column of Table
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 31
The following bit patterns are assigned to the various BAQ Modes:
0002 = 8-to-2 bit Block Adaptive Quantization (normally used SAR mode)
0012 = 8-to-1 bit Block Adaptive Quantization (i.e. sign bit and thresholds, only)
0102 = 8 bit to 0 (no active mode data)
1012 = 8 bits straight (normally used Calibration mode)
1102 = 8-to-4 bit Block Adaptive Quantization (normally used Low Res ALT mode)
1112 = 8-to-4 bit Block Adaptive Quantization (normally used Hi Res ALT mode)
PDS_Object: Column of Table
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 7
Transmit Burst/Receive Window Offset.
The Transmit Burst/Receive Window Offset is the difference between the length of the Transmit Burst and the length of the Receive Window.
conceptual_type: real
number_of_bytes: 4
units: s
minimum_value: -8 PRI
maximum_value: +7 PRI
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: Hz
possible values: 117 kHz, 468 kHz, 935 kHz, 4.675 MHz
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: Hz
possible values: 250 kHz, 1.0 MHz, 2.0 MHz, 10.0 MHz
Total receiver attenuation beams 1 and 2. This value is calibrated using pre-launch test data and is not identical to the nominal value encoded by at1_each.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none (not dB)
minimum_value: 1
maximum_value: 2.512 x 10 7
Total receiver attenuation beam 3. This value is calibrated using pre-launch test data and is not identical to the nominal value encoded by at3_each.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none (not dB)
minimum_value: 1
maximum_value: 2.512 x 10 7
Total receiver attenuation beam 4 and 5. This value is calibrated using pre-launch test data and is not identical to the nominal value encoded by at4_each.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none (not dB)
minimum_value: 1
maximum_value: 2.512 x 10 7
This parameter describes the attenuation for the Microwave Receiver (MR) in the RFES when either Antenna Beam #1 or #2 are selected. The least significant twelve bits actually report three separate attenuators in the RFES MR.
Bits [11, ..., 07] report the commanded attenuation (0dB - 31dB) of attenuator #1 (resolution of 1 dB). Bits [06, ..., 02] report the commanded attenuation (0dB - 31dB) of attenuator #2 (resolution of 1 dB). Bits [01, 00] report the commanded attenuation (0dB - 12dB) of attenuator #3 (resolution of 4 dB). The total nominal attenuation is the sum of the three attenuator settings (in dB).
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 4095
This parameter describes the attenuation for the Microwave Receiver (MR) in the RFES when Antenna Beam #3 is selected. The least significant twelve bits actually report three separate attenuators in the RFES MR.
Bits [11, ..., 07] report the commanded attenuation (0dB - 31dB) of attenuator #1 (resolution of 1 dB). Bits [06, ..., 02] report the commanded attenuation (0dB - 31dB) of attenuator #2 (resolution of 1 dB). Bits [01, 00] report the commanded attenuation (0dB - 12dB) of attenuator #3 (resolution of 4 dB). The total nominal attenuation is the sum of the three attenuator settings (in dB).
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 4095
This parameter describes the attenuation for the Microwave Receiver (MR) in the RFES when either Antenna Beam #4 or #5 are selected. The least significant twelve bits actually report three separate attenuators in the RFES MR.
Bits [11, ..., 07] report the commanded attenuation (0dB - 31dB) of attenuator #1 (resolution of 1 dB). Bits [06, ..., 02] report the commanded attenuation (0dB - 31dB) of attenuator #2 (resolution of 1 dB). Bits [01, 00] report the commanded attenuation (0dB - 12dB) of attenuator #3 (resolution of 4 dB). The total nominal attenuation is the sum of the three attenuator settings (in dB).
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 4095
Radiometer integration period. This parameter is the length of time during which passive signal energy received by the antenna is measured during each radiometer measurement.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
minimum_value: 0.010 s
maximum_value: 0.075 s
Chirp step duration, the duration in time of each single frequency step.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
possible_values: should always be 666.7 ns
Radiometer window counts. The number of times within a "burst" that radiometer measurements occur.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 1
maximum_value: 255
Chirp step quantity, number of frequency changes used to perform a chirp.
(For example, a chirp estimated by two discrete frequencies exhibits one frequency change, hence csq=1.)
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 216
maximum_value: 749
Total length of a chirped signal in time, i.e. csd(csq+1).
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
minimum_value: 0.144 ms
maximum_value: 0.5 ms
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: Hz
minimum_value: 0 Hz
maximum_value: 117.2 kHz
Time from IEB trigger for fast field instruction.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
minimum_value: 0
maximum_value: 65535 (18.2 hours)
Fast field instruction number. The MOS will reset this parameter to zero (000000002) for every Data Take, and will increment this parameter by one for every fast field Instruction. This value will "roll over" from 255 to 0 if necessary.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
Instruction type (fast field=2)
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
possible_value: 2
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
Bursts in Instruction represents to total number of Bursts (i.e., Burst Periods) to be generated per Fast Field Instruction.
Hardware in the DSS maintains a count of the number of Bursts generated for each Fast Field Instruction, and when the appropriate number of complete Burst Periods has elapsed, that hardware generate an interrupt to the Flight Computer, and stops generating Bursts.
If Bursts in Instruction is zero, the DSS is in the so-called "Perpetual Instruction" mode. In this mode, the Digital Subsystem generates waveforms based on a given Fast/Slow instruction pair for an indefinite amount of time (i.e., it will not be limited by the upper range of the bii parameter).
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 255
Burst period. The Burst Period is the total time interval allocated for the transmission of pulses, the receipt of echoes, and the taking of Radiometry data.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
minimum_value: 10 ms
maximum_value: 4.095 s
Pulse repetition interval. This parameter is the time interval between successive transmitted (chirped) pulses.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
minimum_value: 0.002 ms
maximum_value: 4.092 ms
The Receive Window Delay (as defined in the DSS) is measured from the beginning of the first pulse in the first PRI that makes up the Transmit Burst. It includes the PRIs that make up the Transmit Burst and the PRIs between the end of Transmit Burst and the beginning of the Receive Window. The Receive Window Delay will always be an integer number of PRIs.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
minimum_value: 0
maximum_value: 1023 PRI
Chirp start frequency is defined as the frequency of the first frequency step that forms the chirp.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: Hz
minimum_value: 0 Hz
maximum_value: 30 MHz
Most significant 16 bits of the IEB trigger time or the ILX execution time.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
Least significant 16 bits of the IEB trigger time or the ILX execution time.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
Number of calls to the background task during one ETA interrupt period.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 65535
BSL or CROC-FSW delivery date: month.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: month
minimum_value: 1
maximum_value: 12
BSL or CROC-FSW delivery date: day.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: day of month
minimum_value: 1
maximum_value: 31
BSL or CROC-FSW delivery date: year
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: year
minimum_value: 1990
maximum_value: 2010
Raw counts for resistive load measurement.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 4095
Raw counts for antenna (radiometer) measurement summed over all measurement windows.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 2 20 -1
Raw counts for noise diode measurement.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 4095
3 LSBs of Engineering Flight Computer Output Discretes. These discrete bits are: OUT*2, OUT*1 and OUT*0; they correspond to SWD*, TIS* and RMC* in the SDB. See Cassini RADAR DSS High Level Design document Section 4.6.1 for more information.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 7
SubCom row number for this burst. Indicates which elements of engineering telemetry were most recently updated. See Cassini RADAR DSS High Level Design document Section 7.3 for more information.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 15
Twelve Least significant bits of spacecraft clock logged when the Engineering data in this SubCom data set was acquired.
conceptual_type: real
storage_type: unint32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: 4095
Integration time of noise diode measurement.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
minimum_value: 0.0
maximum_value: 0.02
Integration time of resistive load measurement.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
minimum_value: 0.0
maximum_value: 0.08
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Thermistor calibration temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Low noise amplifier temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Envelope detector temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Microwave receiver temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Microwave receiver unit base plate temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Digital chirp generator base plate temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Chirp up converter and amplifier base plate temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Traveling Wave Tube (TWT) temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Electronic power converter (EPC) temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Power supply base plate temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Frequency generator unit base plate temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Thermistor calibration temperature 2.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Energy storage subsystem heat sink temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Beam 1 lower waveguide temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Beam 3 lower wave guide temperature 1.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Beam 3 lower wave guide temperature 2.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Beam 3 lower waveguide temperature 3.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Beam 5 lower waveguide temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Power converter unit temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Radiometer analog to digital converter temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Thermistor extended range calibration temperature #1.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Emitter coupled logic portion temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Engineering flight computer CPU board temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Engineering flight computer memory board temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Science analog to digital converter temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Thermistor extended range calibration temperature #2.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: W
Chirp envelope monitoring point. An envelope reflecting the presence of a DCG output signal is developed by the Digital CHIRP Generator. In effect, this envelope represents each burst of transmission by the RADAR. It will have an amplitude of 2 to 5 volts and widths of 500 microseconds to 75 milliseconds. The envelope is differentially received, peak detected, and then sequentially sampled by the Analog signal Multiplexer. A drooping peak detector level without regenerative resurgence is indicative of delayed or missing envelopes.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none
minimum_value: 100
maximum_value: 4000
The low power level telemetry signal is generated in the RFES. It is the envelope of the transmitted burst out of the CUCA. This envelope has an amplitude of 4 to 5 volts and widths of 500 microseconds to 75 milliseconds. It is differentially received, peak detected, and then sequentially sampled by the Analog Signal Multiplexer. This peak detected output will also produce a decaying level between transmission envelopes, with a resurgence to maximum initiated by each envelope. Each resurgence serving to confirm a transmission. Missing envelopes will identify with a decayed peak detector level.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: W
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
High power amplifier Ku-band transmitter current
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
Secondary line voltage status.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Ultra-stable oscillator temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Energy storage subsystem output voltage.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Conditioned voltage calibration #1.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Power converter unit +5 V voltage.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Power converter unit +5 V current.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
Power converter unit -5 V voltage.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Power converter unit -5 V current.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
Power converter unit +15 V voltage.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Power converter unit +15 V current.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
Power converter unit -15 V voltage.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Power converter unit -15 V current.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
Power converter unit -12 V voltage.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Power converter unit -12 V current.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
Power converter unit 30 V current.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
Phase locked loop 20 MHz frequency.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: Hz
Control and timing unit +5 V current.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none
Power converter unit +9 V voltage.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Power converter unit +9 V current.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
Power converter unit -9 V voltage.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Power converter unit -9 V current.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: A
Conditioned voltage calibration #2.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: V
Inboard shearplate temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Number of transmitted bursts simultaneously in flight. This number is usually 1. The only exceptions are distant scatterometer measurements. For values greater than one the returned echo data from a transmitted burst is not stored in the same record with the radar instrument parameters used to command that burst.
For example, consider the case in which num_bursts_in_flight =2 in record #2 of the file. All of the engineering data segment fields in record #2 refer to the burst transmitted in measurement cycle #2, except num_raw_active_mode_data and rms_raw_active_mode_data which correspond to data received in measurement cycle #2 but transmitted in a previous cycle. The intermediate level data segment field definitions are unaffected by the value of num_bursts_in_flight. The science data segment fields correspond to data collected in measurement cycle #2. The active mode science data fields would (if valid) correspond to a burst transmitted in a previous cycle. (In practice, active mode science data fields will not be valid for num_bursts_in_flight> 1, because distant scatterometry does not have a high enough SNR to compute a measurement for each individual burst. ) In the LBDR file, the active mode data array contains data collected in measurement cycle #2, but transmitted in a previous measurement cycle.
To obtain the active mode data for the burst transmitted in measurement cycle #2 one needs to look ahead num_bursts_in_flight-1 records. For our example (num_bursts_in_flight =2) the received echo data is in measurement cycle #3.
The active mode measurement geometry is always defined for a point in time midway between the centers of the transmit and receive windows in a single measurement cycle. This results in a temporal bias when num_bursts_in_flight> 1.
conceptual_type: integer
storage_type: unint32
number_of_bytes: 4
units: none
Number of valid entries in the time sampled echo data array.
conceptual_type: integer
storage_type: unint32
number_of_bytes: 4
units: none
maximum value: 32000
Root mean square of valid echo data array entries.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none
Flag to indicate quality of intermediate level data segment. Bit 0 is the LSB. The following table indicates the meaning of setting each bit to 1.
Bit 0 Bad or missing s/c attitude data
Bit 1 Other bad of missing geometry data
Bit 2 Missing temperature telemetry (scwg_tmp)
Bit 3 Missing temperature telemetry (feed_tmp)
Bit 4 Missing temperature telemetry (hga_tmp)
Bit 5 Downlink error in raw data file
The other 26 bits are not currently used but are available for future use.
conceptual_type: integer
storage_type: unint32
number_of_bytes: 4
units: none
possible values: 0, 1, 2, 255
Encoded spacecraft clock time. This value is used by the SPICE software employed by the Cassini Navigation Team.
conceptual_type: real
number_of_bytes: 8
units: N/A
Ephemeris time in seconds since J2000.
PDS_Object: Column of Table
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: s
UTC time in yyyy-mm-ddThh:mm:ss.sss format. One space character is padded at the end to ensure file size is a multiple of 4 bytes.
conceptual_type: text
storage_type: ASCII string
number_of_bytes: 24
units: none
UTC time in yyyy-doyThh:mm:ss.sss format. Three space characters are padded at the end to ensure file size is a multiple of 4 bytes.
conceptual_type: text
storage_type: ASCII string
number_of_bytes: 24
units: none
Time offset in seconds from t_ephem_time at which the leading edge of the first transmit pulse leaves the antenna.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: s
t_ephem_time - closest_approach_time. The closest approach time is estimated by the ground processor and included in the value of the DESCRIPTION keyword in the PDS label (header) in UTC format to the nearest ms.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: s
t_ephem_time - epoch_time. The value of epoch_time is usually the same as the closest approach time but may differ occasionally for logistic reasons.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: s
Name of body observed during this burst. Space characters are padded at the end to ensure the string is 16 bytes long.
conceptual_type: text
storage_type: ASCII string
number_of_bytes: 16
units: none
Name of target body fixed frame in the NAIF SPICE system (i.e., "IAU_TITAN"). Space characters are padded at the end to ensure the string is 24 bytes long.
conceptual_type: text
storage_type: ASCII string
number_of_bytes: 24
units: none
Right ascension (east positive longitude in the target centered J2000 celestial sphere) of the North pole of the target body in degrees at the epoch time.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: degrees
Declination (latitude in the target centered J2000 celestial sphere) of the North pole of the target body in degrees at the epoch time.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: degrees
The rotation about the north pole of the target body required to complete the transformation from J2000 to target body fixed coordinates.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: degrees/s
The rotation about the north pole of the target body required to complete the transformation from J2000 to target body fixed coordinates.
Target body fixed coordinates at epoch_time can be computed by successively applying the following three rotations to the J2000 coordinates: pole_right_ascension degrees about the J2000 Z-axis, 90 - pole_declination degrees about the once-rotated Y-axis, and target_rotation_angle degrees about the twice rotated Z-axis.
An additional rotation of target_rotation_rate * time_from_epoch degrees about the thrice rotated Z-axis yields the target body fixed coordinates at t_ephem_time.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: degrees
Ku-band waveguide 3 temperature 9
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
X, Ka, Ku-band feed temperature 5
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
High gain antenna reflector rear temperature 1
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
conceptual_type: integer
storage_type: unint32
number_of_bytes: 4
units: none
possible values: 1, 2, 3, 4, 5
X component of the spacecraft position vector in the J2000 frame.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km
Y component of the spacecraft position vector in the J2000 frame.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km
Z component of the spacecraft position vector in the J2000 frame.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km
X component of the spacecraft velocity vector in the J2000 frame.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km/s
Y component of the spacecraft velocity vector in the J2000 frame.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km/s
Z component of the spacecraft velocity vector in the J2000 frame.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km/s
X component of the spacecraft position vector in the target body frame. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km
Y component of the spacecraft position vector in the target body frame. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km
Z component of the spacecraft position vector in the target body frame. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km
X component of the spacecraft velocity vector in the target body frame. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km/s
Y component of the spacecraft velocity vector in the target body frame. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km/s
Z component of the spacecraft velocity vector in the target body frame. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: km/s
X component of the unit vector in the J2000 frame parallel to the X axis of the spacecraft coordinate system.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Y component of the unit vector in the J2000 frame parallel to the X axis of the spacecraft coordinate system.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Z component of the unit vector in the J2000 frame parallel to the X axis of the spacecraft coordinate system.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
X component of the unit vector in the J2000 frame parallel to the Y axis of the spacecraft coordinate system.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Y component of the unit vector in the J2000 frame parallel to the Y axis of the spacecraft coordinate system.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Z component of the unit vector in the J2000 frame parallel to the Y axis of the spacecraft coordinate system.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
X component of the unit vector in the J2000 frame parallel to the Z axis of the spacecraft coordinate system.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Y component of the unit vector in the J2000 frame parallel to the Z axis of the spacecraft coordinate system.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Z component of the unit vector in the J2000 frame parallel to the Z axis of the spacecraft coordinate system.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
X component of the unit vector in the target body frame parallel to the X axis of the spacecraft coordinate system. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Y component of the unit vector in the target body frame parallel to the X axis of the spacecraft coordinate system. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Z component of the unit vector in the target body frame parallel to the X axis of the spacecraft coordinate system. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
X component of the unit vector in the target body frame parallel to the Y axis of the spacecraft coordinate system. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Y component of the unit vector in the target body frame parallel to the Y axis of the spacecraft coordinate system. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Z component of the unit vector in the target body frame parallel to the Y axis of the spacecraft coordinate system. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
X component of the unit vector in the target body frame parallel to the Z axis of the spacecraft coordinate system. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Y component of the unit vector in the target body frame parallel to the Z axis of the spacecraft coordinate system. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
Z component of the unit vector in the target body frame parallel to the Z axis of the spacecraft coordinate system. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: none
minimum_value: -1
maximum_value: 1
X component of the spacecraft angular velocity vector in the J2000 frame.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: rad/s
Y component of the spacecraft angular velocity vector in the J2000 frame.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: rad/s
Z component of the spacecraft angular velocity vector in the J2000 frame.
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: rad/s
X component of the spacecraft angular velocity vector in the target body frame. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: rad/s
Y component of the spacecraft angular velocity vector in the target body frame. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: rad/s
Z component of the spacecraft angular velocity vector in the target body frame. Value is zero if target name is `NONE' or `CALIBRATION.'
conceptual_type: real
storage_type: float64
number_of_bytes: 8
units: rad/s
Normalized radiometer resistive load measurement.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: counts/s
minimum_value: 0
maximum_value: N/A
Normalized radiometer noise diode measurement.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: counts/s
minimum_value: 0
maximum_value: N/A
Normalized radiometer antenna measurement.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: counts/s
minimum_value: 0
maximum_value: N/A
Quality flag specifying which of the science data elements are valid. Zero value indicates all data fields are valid. The meaning of a set bit (bit =1) is as follows for each bit. (Bit 0 is the LSB).
Bit 0 All passive mode fields are invalid.
Bit 1 All active mode fields are invalid.
Bit 2 All altimeter fields are invalid.
Bit 3 All scatterometer fields are invalid.
Bit 4 All radiometer fields are invalid.
Bit 5 Passive boresight is not on surface.
Bit 6 One or more of passive ellipse points is not on surface.
Bit 7 Active boresight is not on surface.
Bit 8 One or more of active ellipse points is not on surface.
conceptual_type: real
storage_type: int32
number_of_bytes: 4
units: none
minimum_value: 0
maximum_value: N/A
Coefficient used to convert radiometer counts to antenna brightness temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: dB
Antenna contribution to overall system temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Internally generated receiver noise contribution to overall system temperature.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Estimated standard deviation of the residual error in antenna temperature estimate.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: K
Time offset from t_ephem_time for which passive geometry fields are computed. This time is defined to be the mid-point of the summed radiometer windows.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
Angle of orientation of the electric field vector about the look vector during receipt of the passive mode measurement. Angle is zero when the electric field vector is perpendicular to the plane of incidence as defined by the look vector and the target surface normal, and increases counterclockwise.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
The angle between the antenna look direction and the surface normal during receipt of the passive mode measurement.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
The direction of the projection of the antenna look vector in the plane tangent to the surface at the measurement centroid, expressed by the angle counterclockwise from East (e.g. North is 90 degrees).
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Longitude of the passive (one-way) antenna boresight.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of the passive (one-way) antenna boresight.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
Width of major axis of passive best fit ellipse, the distance along the map projection reference sphere between point 1 and point 2.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: km
Width of minor axis of passive best fit ellipse, the distance along the map projection reference sphere between point 3 and point 4.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
Longitude of first point in ellipse representing passive measurement one-way 3-dB gain pattern contour. This point is on the major axis of the best fit ellipse. Each point on the best fit ellipse is computed in the plane tangent to the surface at the boresight and then extended to the reference surface along the line of site of the antenna.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Longitude of second point in ellipse representing passive measurement one-way 3-dB gain pattern contour. This point is on the major axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Longitude of third point in ellipse representing passive measurement one-way 3-dB gain pattern contour. This point is on the minor axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Longitude of fourth point in ellipse representing passive measurement one-way 3-dB gain pattern contour. This point is on the minor axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of first point in ellipse representing passive measurement one-way 3-dB gain pattern contour. This point is on the major axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of second point in ellipse representing passive measurement one-way 3-dB gain pattern contour. This point is on the major axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of third point in ellipse representing passive measurement one-way 3-dB gain pattern contour. This point is on the minor axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of fourth point in ellipse representing passive measurement one-way 3-dB gain pattern contour. This point is on the minor axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Number of pulses which were received completely within the echo window. Partial pulses are ignored.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none
Estimate of the total energy in the receiver window in Joules.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: J
Estimate of the noise contribution to the energy in the receiver window.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: J
Ratio of received signal energy to normalized backscatter cross-section.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
Normalized backscatter cross-section. Quantity is unitless. Scale is physical (linear) not dB (logarithmic).
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none
Normalized backscatter cross-section corrected to minimize dependence on incidence angle. Quantity is unitless. Scale is physical (linear) not dB (logarithmic).
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none
Estimated standard deviation of residual error in normalized backscatter cross-section.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: none
Estimated height of body surface above the center (reference point) determined from the first moment of the compressed waveform after noise subtraction. The quantity is computed by subtracting the measured range to target from the spacecraft distance to body center from the ephemeris. No correction for off-nadir pointing is included. Computed from the active mode data when the radar is in altimeter mode. For other radar modes this data field is invalid, as indicated by science_qual_flag. This value corresponds to the PDS Data Dictionary element definition derived_planetary_radius.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: km
Estimated uncertainty of the surface_height measurement based on the second central moment of the noise-subtracted waveform distribution. This quantity is more a measure of signal spread and surface variation than of "noise" in the measurement itself.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
Time offset from t_ephem_time for which active geometry fields are computed. This time is defined to be the midway between the center of the transmit window and the center of the receive window.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: s
Angle of orientation of the electric field vector about the look vector during the active mode measurement. Angle is zero when the electric field vector is perpendicular to the plane of incidence as defined by the look vector and the target surface normal, and increases counterclockwise. Angle is determined for a time halfway between transmission and receipt of the active mode signal.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
The angle between the antenna look direction and the surface normal halfway between transmission and receipt of the active mode signal.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
The direction of the projection of the antenna look vector in the plane tangent to the surface at the measurement centroid expressed by the angle counterclockwise from East (e.g. North is 90 degrees).
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Longitude of the active (two-way) antenna boresight.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of the active (two-way) antenna boresight.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
Width of major axis of active best fit ellipse, the distance along the map projection reference sphere between point 1 and point 2.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: km
Width of minor axis of active best fit ellipse, the distance along the map projection reference sphere between point 3 and point 4.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
Longitude of first point in ellipse representing active measurement two-way 3-dB gain pattern contour. This point is on the semi-major axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Longitude of second point in ellipse representing active measurement two-way 3-dB gain pattern contour. This point is on the semi-major axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Longitude of third point in ellipse representing active measurement two-way 3-dB gain pattern contour. This point is on the semi-minor axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Longitude of fourth point in ellipse representing active measurement two-way 3-dB gain pattern contour. This point is on the semi-minor axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of first point in ellipse representing active measurement two-way 3-dB gain pattern contour. This point is on the semi-major axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of second point in ellipse representing active measurement two-way 3-dB gain pattern contour. This point is on the semi-major axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of third point in ellipse representing active measurement two-way 3-dB gain pattern contour. This point is on the semi-minor axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of fourth point in ellipse representing active measurement two-way 3-dB gain pattern contour. This point is on the semi-minor axis of the best fit ellipse.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Range to the beginning of the buffer containing the altimeter profile.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: km
Difference in range between consecutive range bins in altimeter profile.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: km
Number of valid entries in altimeter profile.
conceptual_type: integer
storage_type: unint32
number_of_bytes: 4
minimum value: 0
Effective SAR image resolution along azimuth dimension. The value is the width on the ground of a nominal Doppler bin (1bin width = 1/(pulse train duration)) for the current burst multiplied by a constant factor which depends on filter parameters used during azimuth compression.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: km
Effective SAR image resolution along range dimension. The value is the width on the ground of a nominal range bin (1bin width = speed of light/(chirp bandwidth)) for the current burst multiplied by a constant factor which depends on filter parameters used during range compression.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: km
Longitude of the active (two-way) antenna boresight in the BIDR oblique cylindrical map projection.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
Latitude of the active (two-way) antenna boresight in the BIDR oblique cylindrical map projection.
conceptual_type: real
storage_type: float32
number_of_bytes: 4
units: deg
This Appendix describes the Altimeter ABDR Summary file which is created during altimeter processing to provide additional information about the altimeter signal in an easy-to-use, stand-alone format (comma separated value, or CSV). Additional information about the altimeter data as of the generation of this document is also provided to help users understand the information in these data. Following the algorithm descriptions, a brief overview of the altimeter measurement is given.
File name structure: ABDR_SUMMARY_yy_Dzzz_Vnn.CSV, corresponding to the ABDR*.DAT, and the detached label is ABDR*.LBL, where
yy = Radar mode
zzz = 3-digit Radar observation counter (unique through the mission)
nn = 2-digit version number
The structure of the Cassini Radar Altimeter ABDR Summary file is given in the following table.
Each row in the file contains the 17 parameters listed in the table.
Each row in the file represents one burst of data. All pulses within a burst are averaged before the parameters are derived.
The algorithms for producing the items that are not copied from the LBDR are described following the table.
These data are Version 2. The format has been updated to allow predictable record lengths for the PDS SPREADSHEET object. Data produced after January 1, 2008 use the new Radar-determined Titan pole location.
|
Parameter |
Method |
Units |
Format |
Algorithm |
|
SAB Counter |
Copy from LBDR |
Count |
Integer (I9) |
|
|
Spacecraft Event Time (UTC) for beginning of burst |
Copy from LBDR |
None |
UTC yyyy-mm-ddThh:mm:ss.sss |
|
|
Time from closest approach |
Copy from LBDR |
sec |
Float (F8.2) |
|
|
Range to antenna boresight intercept with surface |
First moment of waveform. Not corrected for off-nadir pointing. |
meter |
Integer (F8.0) |
Note: used in surface height correction |
|
Active Centroid Longitude (west 0-360) |
Copy from LBDR |
deg |
Float (F7.2) |
|
|
Active Centroid Latitude |
Copy from LBDR |
deg |
Float (F7.2) |
|
|
Threshold surface height |
From threshold range detection |
meter |
Integer (I8) |
Algo 1 (from center, so ~2575000) |
|
MLE surface height |
MLE estimate of surface height |
meter |
Integer (I8) |
Algo 8 |
|
First moment surface height |
From first moment of waveform range (Range to Surface) |
meter |
Integer (I8) |
Algo 2 (In ABDR field surface_height) |
|
Corrected first moment surface height |
First moment height corrected for off-nadir angle and altitude |
meter |
Integer (I8) |
Algo 3 |
|
Corrected threshold surface height |
Threshold height corrected for off-nadir angle and altitude |
meter |
Integer (I8) |
Algo 4 |
|
Height span of backscatter Distribution ("depth") |
Square root of the second central moment |
meter |
Integer (I8) |
Algo 5 (In ABDR field surf_ht_std) |
|
Skewness of backscatter distribution |
Third central moment normalized |
dimensionless |
Float (F8.2) |
Algo 6 |
|
Incidence angle |
Copy from LBDR |
degrees |
Float (F8.3) |
|
|
Sigma0 |
Calibrated MLE amplitude estimate |
dB |
Float (F8.2) |
Algo 9 (see note) |
|
SNR |
Ratio of peak to estimated noise backscatter value |
dB |
Float (F8.2) |
Algo 7 |
|
MLE fit quality |
Difference between data and model |
% |
Float (F8.2) |
Final value of err_ML in algo 8 |
Algo 1: Threshold Detected Surface Height
Data samples are shifted to put the maximum value at the middle of the received window (1000 points).
A noise level is computed as the average over the first 200 samples.
The threshold bin is the first sample > 15 times the noise level.
The total range is computed by transforming bin with altimeter constants and resolving the range ambiguity.
The corresponding Titan surface height is found without taking into account the slant geometry for the computed incidence angle (see Corrected Threshold Surface Height).
Algo 2: First Moment Surface Height
Data samples are shifted to put the maximum value at the middle of the received window (1000 points).
A noise level is computed as the average over the first 200 samples.
All values < 10 * noise are put to zero (if 10 * noise is > max(data) the threshold 10 * noise is iteratively reduced by dividing by 2).
The first moment bin is estimated as Sum( bin*value ) / Sum( value ).
The total range is computed by transforming bin with altimeter constants and resolving the range ambiguity.
The corresponding Titan surface height is found without taking into account the slant geometry for the computed incidence angle (see Corrected First Moment Surface Height).
( This value corresponds to the PDS Data Dictionary element definition derived_planetary_radius.)
Algo 3: Corrected First Moment Surface Height
The first moment height is corrected for spacecraft range to surface and off-nadir pointing effects based on simulations including surface curvature and RMS surface height over the altimeter footprint as it varies with range.
Algo 4: Corrected Threshold Surface Height
The threshold height is corrected for spacecraft range to surface and off-nadir pointing effects based on simulations including surface curvature and RMS surface height over the altimeter footprint as it varies with range.
Algo 5: Height Span (Depth) -- Square root of second central moment
Data samples are shifted to put the maximum value at the middle of the received window (1000 points).
A noise level is computed as the average over the first 200 samples.
All values < 10 * noise are put to zero (if 10 * noise is > max(data) the threshold 10 * noise is iteratively reduced by dividing by 2).
Bin values relative to the first moment (bin_c) are used to estimate the second moment bin as Sum( bin_c^2*value ) / Sum( value ).
The second moment range is computed by transforming this bin with altimeter constants.
Algo 6: Height Skewness -- Normalized third central moment
Data samples are shifted to put the maximum value at the middle of the received window (1000 points).
A noise level is computed as the average over the first 200 samples.
All values < 10 * noise are put to zero (if 10 * noise is > max(data) the threshold 10 * noise is iteratively reduced by dividing by 2).
Bin values relative to the first moment (bin_c) are used to estimate the third moment bin as Sum( bin_c^3*value ) / Sum( value ).
The third moment range is computed by transforming this bin with altimeter constants.
The value is normalized by dividing by the second moment raised to the 1.5 power.
Algo 7: Signal to Noise Ratio
Data samples are shifted to put the maximum value at the middle of the received window (1000 points).
A noise level is computed as the average over the first 200 samples.
MAX = maximum of data values.
The SNR value is found: SNR=10*log10(MAX/noise) .
Algo 8: Maximum Likelihood Estimate of Height
A model of the expected return for the Cassini altimeter pulse for the given off-nadir angle and RMS surface height distribution is fit to the observed values with an iterative Maximum Likelihood Estimator (MLE). The procedure is widely used in processing ocean altimeter data such as TOPEX and Jason-1. The resulting estimates are usually comparable to the first moment estimates. The algorithm can be confused if the observed pulse is significantly different (e.g., double-peaked) from the assumed model. The solutions intrinsically correct for range and off-nadir effects that must be explicitly corrected for the threshold and first moment estimates. A complete description of this processing is in press for publication in Transactions on Geoscience and Remote Sensing (Alberti et al).
Algo 9: Backscatter (sigma0) Estimate
Constants & definitions:
k=1.38e-23
B = transmitted signal bandwidth
G0 = antenna gain 53.1 dB
sigma_p = sqrt(1/log(2)/8)/B
PT = peak transmitted power (48.084 W)
Lambda = transmitted central wavelength
T = transmitted pulse length
For each fly-by calibration data are processed (ALTH mode).
Data with antenna calibration source are used (csr = 1): to give noise_antenna_mean = mean of power detected data
ATT_cal = value of attenuation used during acquisition of antenna data.
Using system temperature test data (L1=-27 and T1 = 814, L2=-31 and T2=956), the two parameters for the linear approximation of system temperature are found:
b=(T2-T1)/(L2-L1) ; a=T1-b*L1
The system temperature during calibration is found:
T_sys = a + b*10*log10(ATT_cal)
The calibration constant is found:
C = k*B*T_sys/ noise_antenna_mean*ATT_cal
The final value of AMP output of the MLE method (see algo 8) is used to evaluate the final sigma0:
K=(G0^2) * (lambda^2) * c / 2 / ((4*pi)^2) ./ (H^3) * PT .* B .* T .* pi .* sigma_p
sigma_0 = 2./ATT.*AMP*C/K, where ATT = attenuation value used.
NOTE : The AMP value is the amplitude estimate from the MLE. For waveforms that do not conform to the pulse model used in the MLE, the amplitude estimate may not be a good representation of the total backscatter. In particular, for multi-peaked or diffuse waveforms, this value will underestimate the total return power. The SBDR and LBDR files contain a backscatter estimate from the scatterometer processing which does include all returned power.
Overview of Cassini Radar Altimetry
The Cassini RADAR instrument is described in detail in Elachi et al. (2004). The central antenna beam (Beam 3 for SAR) of Cassini's 4-m high gain antenna is roughly circular, with a full-width half maximum of 0.35 degrees (6 milliradians). This beam is used for non-SAR observations, including altimetry. Altimetry is performed with the beam pointed at nadir, and thus altimetry data is confined to short segments of the spacecraft ground track. Typical altimeter observations ("tracks") are 300 to 600 km long. A unique observation was obtained on T30 that was about 3500 km long, much of it over the T28 SAR image swath.
The raw altimeter data product is an echo profile -- intensity versus propagation time delay referenced to the spacecraft clock -- resulting from matched filter processing ("compressing") 10-MHz samples of the frequency-encoded ("chirped", 4.2-MHz bandwidth) pulse to give one-way range resolution of 30 m ("range bin"). Time delay is determined from the echo profile as described above in algorithms 1, 2, 8. The delay corresponds (via a factor of two and the speed of light) to the range to the target. Data are taken in bursts of pulses (typically 15) separated by 1-3 seconds. Determining the surface height relative to a reference point (in this case the center of mass) also depends upon an independent measurement of the position of the point relative to the altimeter. The Cassini-Titan distance is found using the ephemeris determined by the project navigation team. The Cassini-Titan distance is reconstructed after a flyby to an accuracy of better than 100 m. As noted in Section 2.3.2, the spacecraft position and velocity vectors are obtained at the start time of the burst (t_ephem_time). The geometry for altimeter data is calculated at
t_ephem_time + act_geom_time_offset.
Users can compute the spacecraft position at this time using values of the position and velocity in an equation shown generically as
new_sc_pos = sc_pos + act_geom._time_offset * sc_vel
where sc_pos and sc_vel are in the desired coordinate system and the equation applies to each component of the position. Performing this position update is crucial to using the altimeter data (but as noted, it is already done for the altimeter bursts).
The echo profile is defined by the surface radar backscatter cross section as a function of range weighted by the antenna beam pattern. If the beam is not directed vertically (at nadir), the estimated range may not correspond exactly to the altitude. The spacecraft attitude is maintained near nadir-pointing by Cassini's attitude control system. The beam nominally intersects the surface within about 2 milliradians (0.12 degrees, approximately 1/3 of a beam width) of nadir. For the early flybys Ta and T3 when the Titan ephemeris, and thus the relative position of the spacecraft and Titan, was less well-known, the off-nadir angle was somewhat larger than 2 milliradians (mrad). The error from these variations is corrected above in algorithms 3, 4. For off-nadir angles greater than the nominal ~1 mrad, the error grows rapidly.
For locally flat surfaces with ample signal to noise like the Earth's oceans, modeling of the altimeter return in the pulse-limited case using the Brown model (Brown, 1977) can yield range resolutions of better than 0.1 of the nominal range resolution. The early observations of Titan suggested that this model could be applicable to the data so that using the Brown model in a Maximum Likelihood Estimator (MLE) the range could have a precision of a few meters. Unfortunately, later data have shown that the pulses are sometimes more complex than predicted by the Brown model. Improved MLE fits require a better pulse model. The MLE algorithm for single peaked waveforms gives a height estimate similar to that from the first moment. Single peak waveforms occur over most of Titan, the main exception being the brightest, apparently hilly and complex areas.
The figure below shows a "radargram" -- signal strength vs height above the center of Titan for T30. As noted above, T30 was unique in being a very long track of altimeter data (about 3500 km) over the T28 SAR swath. The track goes from a typical altimeter altitude of 10, 000 km above the surface to closest approach at approximately 1000 km. At the lower altitude the antenna footprint becomes much smaller (~6 km rather than ~60 km) providing improved spatial resolution. The second figure below shows the end of the track (the right edge of the first figure -- the along track scales are centered at different places).
The T30 altimeter track provided significant insight into the altimeter data. The main conclusion was that the much of the return width, or "depth, " seen in the radargrams is sub-footprint surface height variation. With this understanding, simulations with RMS surface height variations of approximately 100-200 m and including surface curvature and off nadir pointing are able to reproduce many of the characteristics of the radargrams. After additional analysis, it was decided to include the signal second central moment and the skewness -- the third moment normalized by the second moment as shown in algorithm 6 -- to provide numerical data to represent the depth and complexity seen in the radargrams. As can be seen below, there is small-scale information, usually much smaller scale than the antenna footprint, that cannot be easily conveyed by statistics. Thus, the data in the ASCII file provide a starting point for understanding the altimeter data; but much additional information can be obtained from the waveforms in the ABDR.
References
Alberti, G., L. Festa, C. Papa, and G. Vingione (2008), "A Waveform Model for Near-nadir Radar Altimetry Applied to the Cassini Mission to Titan", IEEETrans. Geosci. Remote Sensing, in press
Brown, G.S. (1977), "The average impulse response of a rough surface and its application, " IEEE Transactions on Antenna and Propagation , AP 25(1) , 67-74.
Elachi, C.; Allison, M. D.; Borgarelli, L.; Encrenaz, P.; Im, E.; Janssen, M. A.; Johnson, W. T. K.; Kirk, R. L.; Lorenz, R. D.; Lunine, J. I.; Muhleman, D. O.; Ostro, S. J.; Picardi, G.; Posa, F.; Rapley, C. G.; Roth, L. E.; Seu, R.; Soderblom, L. A.; Vetrella, S.; Wall, S. D.; Wood, C. A.; Zebker, H. A. (2004), RADAR: "The Cassini Titan Radar Mapper, " Space Science Reviews , 115 , Issue 1-4, 71-110.
Zebker, H.A., Y. Gim, P. Callahan, S. Hensley , R. Lorenz (2008), "Analysis and Intepretation of Cassini Titan Radar Altimeter Echoes", submitted to Icarus .