Gamma ISP: Reference Manual

radcal_PRI

NAME
radcal_PRI Radiometric calibration and format conversion of ESA processed PRI images.

SYNOPSIS
radcal_PRI <PRI> <PRI_par> <GRD> <GRD_par> [K_dB] [inc_ref] [roff] [nr] [loff] [nl]

<PRI>	(input) PRI ground-range image (short integer, sqrt(backscat. intensity))
<PRI_PAR>	(input) SLC parameter file of input PRI ground-range image
<GRD>	(output) calibrated ground-range image (float, backscat. intensity)
<GRD_par>	(output) SLC parameter file of output calibrated ground-range image
[K_dB]	calibration factor in decibels (default: 59.75 dB) ERS1 (D-Paf,ESRIN): 58.24 dB, ERS2 (D-Paf,ESRIN,I-Paf,UK-Paf after 1997): 59.75 dB, ENVISAT ASAR: 55.0 dB (all modes), details see product specifications and ESA publications.
[inc_ref]	reference incidence angle in deg. (default: 23.0 deg.) ENVISAT ASAR: 90.0 deg. (all modes)
[roff]	offset to starting range sample (default=0)
[nr]	number of range pixels to copy (default=0, to end of line)
[loff]	offset to starting line (default=0, 1 header line in the input file is assumed for ERS)
[nl]	number of lines to copy (default=to end of file)

EXAMPLES
radcal_PRI 1352.pri 1352.pri.par 1352.grd 1352.grd.par 59.75 23.0 216 1024 311 1000

Extracts 1000 lines of 1024 range pixels skipping 216 range samples and 311 lines. The data values are radiometrically calibrated and the format is converted from ESA compressed format (short integers) to float.

DESCRIPTION
radcal_PRI extracts the user defined section from the input PRI and writes it out as an ground-range intensity image (GRD) file. The format is converted from short integer magnitude to floating point intensity. A new GRD parameter file is created to describe the geometry of the output image. Starting, center, and ending times, and the near, center and far ground ranges are calculated for the exrtracted segment.

For further processing the special geometry of the ground-range images (which deviates from the range Doppler geometry of the slc images) has to be taken into account. As a consequence not the geocoding programs written for the range Doppler geometry but the special programs for geocoding of gorund-range images are used. For the first range pixel and first azimuth line of the input PRI to coincide with the output image select roff=0 and loff=0, respectively. For the input PRI (in ESA compressed format) the program assumes that there is 1 header line. For the output GRD there is no header line at the start of the file. The input PRI (in ESA compressed format) typically has a 12 Byte file header, as documented in the PRI parameter file. The output GRD file has no file header.

For ERS PRI data the radiometric calibration uses the procedure specified by ESA in the ERS SAR Calibration documentation. There you also find a more complete list of calibration constants for different ESA Pafs. The digital numbers of the PRI product are squared, multiplied with the calibration constant, and multiplied with the ratio between the sine of the incidence angle and the sine of the reference incidence angle (value = DN*DN*K*sin(inc)/sin(inc_ref)).

For ENVISAT ASAR PRI data the radiometric calibration uses the procedure specified by ESA in the ASAR documentation. The digital numbers of the PRI product are squared, multiplied with the calibration constant, and multiplied with the the sine of the incidence angle (value = DN*DN*K*sin(inc)), which corresponds to the procedure used for ERS with a reference incidence angle of 90.0 degrees. The calibration constant shall be 55.0 dB for all ASAR modes. For early data products this may not be valid though. Please check more complete information on the calibration constants as provided by ESA.

OPTIONS
The selected image section may extend outside of the range of valid data of the input PRI. The NULL value assigned to these pixels is (0.0,0.0).

Ground-range image can be converted to slant-range geometry using the program GRD_to_SR.

SEE ALSO
par_PRI, GRD_to_SR, SR_to_GRD.