SIR-C Sample Data Set

by Bruce Chapman, Anthony Freeman, and Patti Barrett

Jet Propulsion Laboratory

The Spaceborne Imaging Radar - C (SIR-C) is a unique imaging system designed to look at the Earth's environment using radars of different wavelength and polarizations. SIR-C was flown on the Space Shuttle Endeavour in April and October, 1994 and collected data over many sites of scientific interest around the globe. To find out more about SIR-C, take a look at the NASA/JPL imaging radar home page on the World Wide Web at http://southport.jpl.nasa.gov/ .

SIR-C data is stored in a special format unique to fully polarimetric (i.e. both horizontal and vertical transmit and receive polarizations) Synthetic Aperture Radar (SAR) data, and achieves an efficient compression ratio with little loss in information. In addition, the Committee on Earth Observing Systems (CEOS) has defined a structure for SAR data and the headers that accompany it. A CEOS data set consists of 3 files : a leader file, an image file, and a trailer file. In addition, each tape has a volume descriptor. This structure, called the CEOS format, defines the file structure of the SIR-C data as it is found on CEOS format tapes.

This document briefly describes two tapes : a CEOS format tape and a tar (unix) tape. The CEOS format tape is similar to data normally distributed by NASA. The tar tape contains this document, two other readme files describing the data format in detail, and 6 directories containing SIR-C SAR data from the CEOS tape in various formats, after being decoded by JPL developed CEOS reader software.

Software has been written to read this data from tape, write it to disk, decode the CEOS headers, decompress the data, average the data, synthesize byte images, and convert between various other common formats. This software may be obtained from the SIR-C project by contacting Ellen O'Leary at the Radar Data Center, Jet Propulsion Laboratory, Pasadena, California, USA 91109 (fax : 1-818-393-2640). (Software information may also be found at the World Wide Web server for NASA/JPL imaging radar data at http://southport.jpl.nasa.gov/ )

This sample data set has been prepared to illustrate the data formats of SIR-C data. Example data from each of the following has been prepared:

Single Look Complex (SLC) - Compressed Scattering Matrix data. May be single (4 bytes per pixel), dual (6 bytes per pixel), or Quad (10 bytes per pixel) pol. (Example data is quad pol, meaning that four polarizations are included.)

Multi Look Complex (MLC) - Compressed cross-products of the Stokes Matrix data. May be dual (5 bytes per pixel), or Quad (10 bytes per pixel). (Example data is quad pol.)

Multi Look Detected (MLD) - Compressed single pol power values (2 bytes per pixel).

A detailed description of these data formats may be found in the SIR-C data format description file (Readme.dataformat).

CEOS data consists of the CEOS leader file, the CEOS imagery file, and the CEOS trailer file. In addition, each CEOS tape contains a volume descriptor record. A detailed description of the CEOS format may be found in the SIR-C CEOS description file (Readme.ceosdesc).

Two tapes are provided with this document. One tape is a tar (unix) tape, and should be tar'd to disk. Contained within this tape are this readme file; the above mentioned readme files : (Readme.dataformat, Readme.ceosdesc) ; and 6 directories (one for each wavelength and data type MLC, MLD, or SLC). Within each directory are the decoded CEOS files, and gif images of the data file, along with miscellaneous output files. The other tape is a CEOS tape, and contains just the CEOS files described in Readme.ceosdesc.

Two examples of each data format were created, one for each wavelength (L-band = 24 cm, and C-band = 6 cm). The scene for all examples are of Stovepipe Wells, Death Valley, California. The CEOS tape contains the following:

Product 1 : pr10141_ldr_ceos (CEOS leader file)

pr10141_img_ceos (CEOS image file) L-band SLC data 220 MB

pr10141_ldr_ceos (CEOS trailer file)

Product 2 : pr10142_ldr_ceos (CEOS leader file)

pr10142_img_ceos (CEOS image file) C-band SLC data 220 MB

pr10142_ldr_ceos (CEOS trailer file)

Product 3 : pr50141_ldr_ceos (CEOS leader file)

pr50141_img_ceos (CEOS image file) L-band MLC data 13 MB

pr50141_ldr_ceos (CEOS trailer file)

Product 4 : pr50142_ldr_ceos (CEOS leader file)

pr50142_img_ceos (CEOS image file) C-band MLC data 13 MB

pr50142_ldr_ceos (CEOS trailer file)

Product 5 : pr70141_ldr_ceos (CEOS leader file)

pr70141_img_ceos (CEOS image file) L-band MLD data 3 MB

pr70141_ldr_ceos (CEOS trailer file)

Product 6 : pr70142_ldr_ceos (CEOS leader file)

pr70142_img_ceos (CEOS image file) C-band MLD data 3 MB

pr70142_ldr_ceos (CEOS trailer file)

The MLC and MLD sample data were generated from calibrated SLC data. It will differ in minor ways from actual MLC and MLD CEOS data tapes as distributed by NASA:

1. The data is approximately projected onto a flat Earth surface. The pixel spacing (36 meters) is different from the standard (NASA distributed) pixel spacing (12.5 meters). The number of independent samples averaged to form each pixel (number of looks) is 18, rather than the standard ~5 looks.

2. The file names of the data are simulated processing run numbers. The CEOS headers assume that the processing run number is 10141 and 10142. Auxiliary files such as histogram files generated by the ceos_reader software will therefore be named pr10141_histoplot_*

3. A normal CEOS tape will have only one data type (SLC, MLC, or MLD) on a tape.

4. The MLD data set is single polarization data (H transmit, H receive) that was extracted from the fully polarimetric SLC data.

5. The SLC data is the highest resolution data format, typically with resolution of 8 meters. For NASA-supplied SIR-C CEOS MLD or MLC data, the resolution will usually be 18 meters. For the MLC and MLD data provided on this sample data set, the CEOS header indicates that the resolution is 0.0 meters, rather than the actual 60 meters.