Gamma DIFF & GEO Reference Manual

offset_pwr_list

offset_pwr_list measures offsets between SLC images at positions specified by a list of coordinate pairs using intensity cross-correlation

SYNOPSIS
offset_pwr_list <SLC-1> <SLC-2> <SLC1_par> <SLC2_par> <OFF_par> <clist_RDC> <clist_MAP> <offs> <snr> <nx> <ny> [rwin] [azwin] [offsets] [n_ovr] [thres] [pflag]

<SLC-1>	(input) single-look complex image 1 (reference)
<SLC-2>	(input) single-look complex image 2
<SLC1_par>	(input) SLC-1 ISP image parameter file
<SLC2_par>	(input) SLC-2 ISP image parameter file
<OFF_par>	(input) ISP offset/interferogram parameter file
<clist_RDC>	(input) list of x,y pixel coordinates in the map projection geometry (text format)
<clist_MAP>	(output) list of x,y pixel coordinates in the reference SLC image geometry (Range-Doppler Coordinates) (text format)
<offs>	(output) offset estimates (fcomplex)
<snr>	(output) offset estimation SNR (FLOAT)
<nx>	width of offset map
<ny>	height of offset map
[rwin]	search window size (range pixels, (enter - for default from offset parameter file))
[azwin]	search window size (azimuth pixels, (enter - for default from offset parameter file))
[offsets]	(output) range and azimuth offsets and SNR data in text format, enter - for no output
[n_ovr]	SLC oversampling factor (integer 2**N (1,2,4) default = 2)
[thres]	offset estimation quality threshold (enter - for default from offset parameter file)
[pflag]	print flag (0:print offset summary (default) 1:print all offset data)

EXAMPLE
offset_pwr_list 19970924_seg.slc 19971018_seg.slc 19970924_seg.slc.par 19971018_seg.slc.par off clist_RDC clist_MAP offs_clist snr_clist 724 315 64 64 offsets_clist 2 6.5

estimates the range and azimuth offsets at a list of coordinate positions specified in the clist_RDC file.

DESCRIPTION

offset_pwr_list estimates the range and azimuth offset filed cross correlation optimization of the detected SLC data. This cross correlation optimization algorithm rapidly generates the offset fields by correlating image chips. The image chips are nominally square and have sizes in the range of 16 to 128 depending on the interferogram correlation. The positions of these image chips is specified in SLC coordinates by entries in the clist_RDC file. This file consists of pairs of integers, one pair per line, specifying the range sample number and azimuth line number for the chip center.

Oversampling of the SLC images prior to measurement of the offsets is supported with a nominal vvalue of 2. IThe location of the correlation maximum is estimated using a two-dimensional quadratic least squares fit of the 2-dimensional correlation function.

The range and azimuth sizes of the image chips used in the search, the SLC over-sampling factor, and the signal to noise (SNR) threshold can be entered on the command line. Default values are taken from the ISP offset/interferogram parameter file. Recommended values are suggested as default values in the program create_offset. For the SNR threshold, values of 7.0 and larger are recommended. Values entered while running create_offset for the number of range and azimuth positions are ignored by offset_pwr_list, since the locations for offset estimation are in the clist_MSP.

The range and azimuth offset estimates are written to a binary data file (fcomplex format) with the offsets coded as pairs of floating point numbers (range offset, azimuth offset). The SNR values are also written to a float data file. The offset and SNR values can also be written to a text format file that contains the range and azimuth positions, offsets, and SNR value. The dimensions of the array for the offset measurements nx and ny can be obtained from the DEM_pwr2 output by dem_RDC_list. One approach to display of the offset results is to scale the geocoded image by the sub-sampling factors entered when running dem_RDC_list. In this way there is 1 pixel for every point where offsets are measured.

A typical processing sequence is described in the GEO Users Guide section 15 and section H.(Measuring range and azimuth offsets on a regular grid in map coordinates).
typedef_ISP.h, dem_RDC_list, ras_clist