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MRO SHARAD REDUCED DATA RECORD V1.0 (PDS)

NSSDCA ID: PSPG-00885

Availability: Archived at NSSDC, accessible from elsewhere

Description

This description was generated automatically using input from the Planetary Data System.

Data Set Overview

Data Set MARS RECONNAISSANCE ORBITER MARS SHARAD REDUCED DATA RECORD V1.0 (Level 1B data) consists of received echoes that have been Doppler filtered, range compressed, and converted to complex voltages, correlated with the auxiliary information needed to locate observations in space and time and to process data further. Level 1B data users are expected to be mainly geologists interested in determining the structure of the shallow Martian subsurface. Data users must be aware that processed echoes may contain artifacts due to off-nadir surface reflections, the socalled clutter, reaching the radar after nadir surface echoes, and thus appearing as subsurface reflections. Processing ========== SHARAD RDR Data Products are generated at the SHARAD operation center in Rome, Italy, under the responsibility of the Team Leader Institution (INFOCOM Department, University of Rome 'La Sapienza'). In the processing producing RDRs, data are range- and Dopplerprocessed. The software used to produce RDR data products requires a configuration file containing values for parameters used by the processing algorithms. Once the parameters are set, data processing proceeds in a fully automated way. Level 1B processing consists of the following functions: 1) Auxiliary data loading 2) Data selection 3) Data healing 4) Phase distortion compensation 5) Doppler parameters estimation 6) Range-Doppler processing 7) Multi-look processing 8) Output generation Auxiliary data loading consists in the loading of files needed in the processing. Such files are part of the SHARAD Level 1A (EDR) archive, which thus constitutes the sole input for the production of RDR data products. They are the antenna pattern file, describing the SHARAD antenna relative gain as a function of the spacecraft high-gain antenna and solar panels position; the reference function file, that is the complex conjugate of the FFT of the discretely-sampled transmitted signal; and the spurious frequencies file, reporting the spectrum of coherent noise produced by the spacecraft electronics within the SHARAD operation bandwidth. Data selection consists in the loading of the Level 1A data products to be processed and of the configuration file setting parameters required by processing algorithms. During this phase, each sample of each raw echo, compressed on-board into a 4-, 6- or 8- bit integer, is decompressed according to two different algorithms, depending on the selection of either static compression or dynamic compression for on-board processing. If a static compression has been adopted, then the uncompressed value is given by S32 = S4,6,8 / 2N where S32 is the sample in 32-bit floating point notation, S4,6,8 is the compressed value of the sample, and N is the number of presummed echoes. If dynamic compression has been adopted, then S32 = S4,6,8 / 2p where p is the SDI Bit-Field parameter reported into the Science Ancillary Data. Data healing consists of the compensation of antenna pattern variations caused by the movement of the spacecraft high-gain antenna and solar panels during the data take, and of the removal of spurious signals introduced by the spacecraft electronics. Phase distortions may occur due to interaction between the radar signal and the Martian ionosphere plasma, whose refraction index is a function of frequency. Phase distortion compensation is a fully automated function implementing the Phase Gradient Autofocus (PGA) algorithm. Doppler parameters estimation produces estimates of the Doppler centroid frequency and of the Doppler bandwidth for the raw data. Doppler centroid estimation determines the average Doppler frequency of received echoes in order to perform an optimum azimuth filtering. The centroid frequency is the frequency dividing the energy spectra of averaged signals in two equal parts. The Doppler bandwidth determines the maximum possible azimuth resolution of the output echoes, and the amount of data overlapping from one synthetic aperture to the next. Range-Doppler processing consists of range compression followed by Doppler processing. Range compression consists in the matched or inverse filtering of each raw echo. The filtering is performed by multiplying the raw signal FFT spectrum by the reference function (matched filtering) or by its inverse (inverse filtering). Doppler processing is performed through the Chirp Scaling Algorithm (CSA) for SAR processing, which allows also for Range Cell Migration Compensation (RCMC). CSA guaranties good performances in terms of computational speed and achievable azimuth resolution. Multi-look processing aims at reducing speckle: the random fluctuations of received power due to coherent reflections, by averaging the values of neighboring range-Doppler pixels within a given window around each pixel. Such filtering will increase the radiometric resolution, but the spatial resolution will decrease as a result. The window size is fixed, while the window weight is selectable by means of the configuration file. In the generation of the output files, the processed echoes, now a complex quantity because of the processing taking place in the Fourier spectral domain, are complemented with the original auxiliary data contained in the scientific telemetry of the instrument, with parameters characterizing the ground processing of the echoes, with geometric quantities generated on-ground from spacecraft navigation data, and with parameters extracted from instrument and spacecraft housekeeping telemetry. All this auxiliary information, with the exception of processing parameters, is copied from the input Level 1A files used to produce the RDR data product. Data ==== Each SHARAD RDR data product is the result of the processing all echoes acquired continuously in time using the same operation mode, instrument status and on-board processing scheme. There is one RDR data product for every SHARAD Experiment Data Record data product acquired in subsurface sounding mode, which in fact constitutes the input for the RDR product generation. The content of each SHARAD RDR data product is highly variable in terms of number of processed echoes, and depends on how operations for the instrument were planned during a given data collection period. Each processed radar observation in an RDR data product is the result of range and azimuth processing of a variable number of raw echoes. Thus, although there is a one-to-one correspondence between EDRs and RDRs, such correspondence does not hold between individual raw and processed echoes: in general, many raw echoes (of the order of several tens or a few hundred) result in the production of a single processed echo. Because each processed echo is a sequence of time samples of a received signal, complemented by ancillary information, the natural organization for processed echoes within a Data Product is a table, in which each line contains data from a single processed echo, and each column contains the value of a single parameter or time sample across different processed echoes. Each Data Product consists of two files: 1) A binary file containing the scientific data of the instrument: a sequence of processed echoes, each of which is preceded by a header containing information on the instrument setting and onboard processing of the data, and followed by parameters characterizing the ground processing of the echoes, by geometric quantities generated on-ground from spacecraft navigation data, and by parameters extracted from instrument housekeeping telemetry. 2) A detached ASCII PDS label file describing the content of the data product. Ancillary Data ============== Ancillary data describe the instrument settings during data acquisition and report parameters used in on-board processing. Scientific data consist of the processed complex echo, expressed as a vector for the real part of the complex echo, followed by a second vector of the same length containing the imaginary part of the echo. Processing parameters have been computed by the ground processing software, and contain information such as the Doppler centroid and Doppler bandwidth of original raw echoes. Geometric parameters have been computed on ground from spacecraft trajectory and attitude data, and allow the location of each processed echo in space and time. Instrument engineering parameters are extracted from SHARAD housekeeping telemetry and report quantities such as currents and temperatures within the instrument. Coordinate System ================= SHARAD RDR data products conform to a Project-determined set of cartographic standards. All map-projected data use planetocentric coordinates and east-positive longitudes in the range 0 to 360 degrees, computed w.r.t. the IAU 2000 reference ellipsoid. Vector quantities such as spacecraft positions are expressed in a Cartesian planetocentric reference frame. Media/Format ============ Each SHARAD RDR data product consists of a binary file in fixed record-length format, and a detached PDS label containing information on source data, production process, relation between stored bytes and physical quantities, product identification, storing and organizing of ancillary data and descriptive information needed to interpret and process the data. The structure of data contained in the binary file is that of a PDS Table object. The PDS label contains pointers to a file containing definitions of the columns of such Table object. Each record in a binary file is a processed echo: the result of the Doppler filtering and range compressing of a variable number of raw echoes, and is expressed as a time series of complex voltages. Each record also contains a number of parameters describing the operation of the instrument during data acquisition, together with engineering and spacecraft information. Specifically, each record is subdivided into five parts, each of which contains a different type of information: ancillary data, scientific data, processing parameters, geometric parameters and instrument engineering parameters. PDS labels are written in Object Description Language (ODL). 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. The labels contained in SHARAD EDR files conform to the general structure used for all PDS detached labels.

These data are available on-line from the Planetary Data System (PDS) at:

http://pds-geosciences.wustl.edu/mro/mro-m-sharad-4-rdr-v1/

Alternate Names

  • MRO-M-SHARAD-4-RDR-V1.0

Discipline

  • Planetary Science: Geology and Geophysics

Additional Information

Spacecraft

Experiments

Questions and comments about this data collection can be directed to: Dr. David R. Williams

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Roberto SeuData ProviderUniversita degli Studi di Romarobseu@infocom.uniroma1.it
Dr. Roberto OroseiGeneral ContactIstituto Nazionale di Astrofisicaroberto.orosei@iaps.inaf.it
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