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| USGS Earth Resources Observation and Science Center (EROS) |
A portion of the second flight of SIR-C/X-SAR (Mission Elapsed Time days 7, 8, 9, and part of day 10) was devoted to collecting a series of repeat pass interferometry data_takes collected at sites all over the world. In addition, nine data_takes were collected that were repeat passes of data_takes collected on the first flight of SIR-C/X-SAR in April 1994. All the interferometry data_takes are summarized in a table.
In order to collect these interferometry data, the shuttle's orbit was circularized so that the same targets would be passed over with the same viewing geometry every 24 hours. The radar configuration (look angle, radar mode, bandwidth, pulse repetition frequency, etc.) was identical for each data_take over a site. The data that were collected on most of the SIR-C interferometry data_takes are Mode 20: L-band VV and C-band VV, both collected at 40 mHz bandwidth. Dual and quad polarization data (HH, HV, VV, and VH) were collected on some of the interferometry passes. X-SAR data (X-band VV polarization) were also collected as part of the repeat pass interferometry experiment.
The passes that were collected are quite long, some crossing whole continents. This was done to increase the chances that at least a portion of the data pass would yield successful interferometry results.
Since these data were collected on an experimental basis, the data set and interferometry products generated by the SIR-C processor are not well documented. However, the SIR-C/X-SAR repeat pass interferometry experiment is considered a success and many results have been obtained to date. Most of the research on this dataset has been done at the Jet Propulsion Laboratory, the DLR in Germany, and also at a few universities. Some references, a report on interferometry, and a short DEM generation tutorial are available.
The SIR-C processor produced two types of interferometry data products: interferometric single-look complex (iSLC) products and raw interferograms. In addition, some researchers use the Reformatted Signal Data (RSD) product to generate interferograms.
At least two data_takes from a repeat pass suite of data_takes (2 to 4 data_takes) were identified for each interferometry data product.
iSLC products are frame products and can be processed for the same area from two or more repeat pass data_takes from a given suite. The iSLC product is a CEOS-formatted frame image that is 50 km along the flight track by the swath width (which varies with the viewing geometry and the radar mode). iSLC's are distributed in CEOS format on DVD. As with all CEOS distribution products, CEOS_reader software or direct import capability is required. The image is in slant range with natural spacing and is full resolution. Typically the files are hundreds of megabytes in size for each scene. iSLC's are uncalibrated SLC images that are processed with the same Doppler centroid (for all data_takes requested) to allow interferometric processing.
RSD products are not technically interferogram products, however some researchers have used them to generate interferograms. RSD products are frame products (100 km along track) in the CEOS format and were processed for the same area from two or more repeat pass data_takes from a given suite.
The raw interferogram products are distributed on DVD in TAR format and contain the files listed below. Two processing runs were combined for each frequency to produce interferograms for L-band and C-band. The interferograms and the detected (backscatter amplitude) images have had 4 looks in the azimuth direction (four pixels averaged).
The following files are included in the raw interferogram data product (all file names start with a 5 character processing run number):
| #####.pfile | ASCII format file that contains processing parameters; there are four pfiles for each raw interferogram, two each for the L-band and C-band data |
| #####_det | Detected image file for the processing run; 4 bytes/pixel; there are four det files for each raw interferogram, two each for the L-band and C-band data |
| #####_display_xx | Byte version of the detected images, with xx representing the polarization of the data |
| #####_ephemeris | ASCII format file of ephemeris data |
| #####_offset | ASCII format file of pixel offsets measured during image formation |
| #####_photo_image | reduced version of the display file |
| #####_raw_interf | raw interferogram; 8 bytes/pixel complex interferogram |
The following caveats apply to these data products.
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