first header: general information about data file including
# of lines and samples and offset to the first data record.
parameter header: information specific to the scene
calibration header: information on data calibration
DEM header: only present for TOPSAR data; contains the elevation offset and elevation increment needed to translate the integer*2 values to elevations in meters.
HH horizontally polarized transmit wave, horizontally polarized receive
HV horizontally polarized transmit wave, vertically polarized receive wave
VH vertically polarized receive wave, horizontally polarized receive wave
VV vertically polarized receive wave, vertically polarized receive wave
File Name Data Format File Size
CM####_c.dat compressed Stokes matrix data in slant range 15 Mbytes
CM####_l.dat compressed Stokes matrix data in slant range 15 Mbytes
CM####_p.dat compressed Stokes matrix data in slant range 15 Mbytes
Note: Due to FCC restrictions, since 1994, P-band data are not included for POLSAR datasets collected at 40 MHz bandwidth over sites in the United States.
The “CM” indicates that the data are in a compressed Stokes matrix format. CM is followed by a four-digit output product number; this number is unique for each scene.
CM data are oriented so that each pixel sample is decreasing azimuth (along track) and each pixel line is of increasing range (cross-track).
POLSAR data processed on Version 5.1 or Version 6.1, the integrated
Data collected since 1993 are processed using Version 5.1. These data are in TAR format and can be read from the tape using TAR commands.
POLSAR data processed on Version 3.56, the VAX processor:
Data collected prior to 1993 are processed using Version 3.56 and are read by using the following steps. These steps apply to both the frame product (which will have a CM in the file name) and also the synoptic data product (which will have an SY in the file name).
1. After you have put the tape into your tape drive, type: tcopy (device
Device name is the name of your tape drive and is specific to your system.
This will result in an informational listing about each of the
files on the tape which will look something like:
file 1 : records 1 to 1282 : size 10240
file 1 : eof after 1282 records : 13127680 bytes
In the case of CM data, the first two or three files (depending on whether P-band data were collected) will be the data files for each frequency. In the case of synoptic data, the first three files will be the three frequency-polarization. The remaining files are files that contain positional information and are not needed to generate images.
The record size for each file (10240 in the example shown above) should be recorded for use in extracting the files off the tape.
2. Read the Tape
Type the following command to read the data off the tape:
dd if = /dev/exa# of = (output file name) bs = 10240
if = input file (in this case, the data are on the tape device)
of = user-provided output file name (e.g. DeathValley_p.dat)
bs = the number of bytes per record (from step 1.)
Once the files have been extracted from the tape, you can use the “more”
command to see the contents of the New Header.
TOPSAR data are processed on the AIRSAR Integrated Processor (ver. 5.1
or ver. 6.1).
File Name Data Description Data Format
File Size (10 km)
DEM Data (C-band, maybe L-band)
TS####_c.vvi2 C-band VV polarization only integer2 (signed 16 bit) 2.5 Mbytes
TS####.demi2 C-band DEM integer2 (signed 16 bit) 2.5 Mbytes
TS####.corgr correlation coefficient map byte file 1.2 Mbytes
TS####.incgr local incidence angle map byte file 1.2 Mbytes
TS####_l.datgr L-band polarimetry compressed Stokes matrix data 15 Mbytes
TS####_p.datgr P-band polarimetry compressed Stokes matrix data 15 Mbytes
Note: Due to FCC restrictions, since 1994, P-band data are not included for TOPSAR datasets collected at 40 MHz bandwidth over sites in the United States.
The “TS” indicates that the data are TOPSAR data. TS is followed by a four-digit output product number that is unique for each scene. All TOPSAR data, including any polarimetric data collected in a TOPSAR mode, will be projected in the ground range (this is indicated by the “gr” in the file extensions shown above).
Reading TOPSAR Data
Data collected since 1993 are processed using Version 5.1 and Version 6.1. These data are in TAR format and can be read from the tape using TAR commands or from a CD-ROM directly. Note that the integer*2 data will need to be converted using the following equations:
to convert demi*2 data to elevations in meters:
hs = (elevation increment) * DN + (elevation offset)
The elevation increment and offset are found in the DEM header record. DN is the integer*2 (signed) number from the .demi2 data file.
to convert vvi*2 data to radar cross sections
sigma naught = (DN**2)/(General Scale Factor)
DN is the integer*2 (signed) number as the amplitude (linear value) from the .vvi2 data file and the General Scale Factor (GSF) is in the second field of the Calibration Header. Note that the GSF = 10**6
Polarimetric data collected in the TOPSAR mode are read the same way
as POLSAR data.