Gamma ISP: Reference Manual

SLC_intf

ANSI-C program: SLC_intf.c

NAME
SLC_intf Multi-look complex interferogram generation from registered SLC in fcomplex format.

SYNOPSIS
SLC_intf <SLC-1> <SLC-2R> <SLC1_par> <SLC2R_par> <OFF_par> <interf> <rlks> <azlks> [loff] [nlines] [sps_flg] [azf_flg] [rp1_flg] [rp2_flg] [SLC-1s] SLC-2Rs][SLC-1s_par] [SLC-2Rs_par]

<SLC-1>	(input) SLC-1, reference geometry (fcomplex)
<SLC-2R>	(input) SLC-2, coregistered to SLC-1 (fcomplex)
<SLC1_par>	(input) SLC parameter file of SLC-1
<SLC2R_par>	(input) SLC parameter file of SLC-2R
<OFF_par>	(input/output) ISP offset/processing parameter file
<interf>	(output) multi-look complex interferogram (with range phase)
<rlks>	number of range looks for multi-looking
<azlks>	number of azimuth looks for multi-looking
[loff]	offset to starting line relative to SLC-1 for interferogram (default=0)
[nlines]	number of SLC lines to process (default = to end of file)
[sps_flg]	range spectral shift flag: 1: apply spectral shift filter (default) 0: do not apply spectral shift filter
[azf_flg]	azimuth common band filter flag: 1: apply azimuth common band filter (default) 0: do not apply azimuth common band filter
[rp1_flg]	SLC-1 range phase mode 0: nearest approach (zero-Doppler) phase 1: ref. function center (Doppler centroid) (default)
[rp2_flg]	SLC-2 range phase mode 0: nearest approach (zero-Doppler) phase 1: ref. function center (Doppler centroid) (default)
[SLC-1s]	SLC-1 after range spectral shift and azimuth common-band filtering (FCOMPLEX format)
[SLC-2Rs]	SLC-2R after range spectral shift and azimuth common-band filtering (FCOMPLEX format)
[SLC1s_par]	SLC-1s ISP image parameter file
[SLC2Rs_par]	SLC-2Rs ISP image parameter file

EXAMPLE
SLC_intf 1352.slc 1610.rslc 1352.slc.par 1610.rslc.par 1352_1610.off 1352_1610.int 1 5 0 1 1

DESCRIPTION
SLC_intf reads the two co-registered, single look complex SAR images SLC-1 and SLC-2R, the corresponding SLC parameter files SLC-1.par and SLC-2R.par and the ISP offset/processing parameter file OFF_par and computes the multi-look interferogram. The complex (normalized) interferogram is defined by:

complex interferogram = <s1s2*>/sqrt(<s1s1*><s2s2*>.

s1 and s2 are the single look complex values of SLC-1 and SLC-2, * stands for conjugate complex, i.e, (a+jb)* = (a-jb), < > stands for the ensemble average. For a multi-look interferogram pixel < > is estimated by (coherent) averaging of the single look values.

The argument of the complex interferogram corresponds to the interferometric phase. The magnitude of the complex interferogram corresponds to the interferometric correlation derived from the number of interferometric looks used in the multi-looking. Real and imaginary values of the complex (normalized) interferogram are written as output to the interf file.

Range spectrum filtering is applied using the sps_flg command line option. This filtering accounts for the spectral shift induced by the difference in incidence angles between SLC-2 and SLC-1 due to the baseline. Only the range spectrum interval common to the the two SLC images is retained.

Due to the fact that the 2 SLCs are coregistered no resampling/interpolation step is required. To coregister multiple SLC images there are several different possibilities. The registration offset function is determined using the programs offset_pwr, offset_SLC, and offset_fit. The resampling of the SLC to the reference geometry is then completed using the program SLC_interp.

Another approach to generating an interferogram is to use the DIFF/GEO program SLC_interp_lt that uses a lookup table to resample the SLC images. After the initial resampling, a refinement using measured offsets of the resampled image and the reference is performed. The resampling lookup table is created using the DIFF/GEO program rdc_trans.

SLC_intf also supports generation of interferograms with SLC data acquired with sensors having different radar center frequencies such as ERS and ENVISAT. The radar instruments on these platforms differ in carrier frequency by 30 MHz. When the carrier frequencies of the two SLCs are different, SLC_intf applies a range phase correction proportional to the slant range.

No multi-look intensity images are produced from the two SLC images by SLC_intf. Coregistered multi-look intensity images in the identical geometry as the interferogram can be generated from the co-registered SLC images using the program multi_look.

Display of the images can be carried out by ISP programs for complex and intensity data. Complex images can be displayed or saved as SUN raster or BMP format files using the programs dismph, dismph_pwr, rasmph, rasmph_pwr. Intensity images can be displayed using programs dispwr, dis2pwr, raspwr.

The program also has the option to perform azimuth common band filtering prior to interferogram formation using the azf_flg command line option. This azimuth filtering retains only the common segment of the azimuth image spectrum to optimize the correlation.

SLC data can be provided that follows either the zero-Doppler or squinted (Doppler-centroid) range phase convention. In the zero-Doppler convention the phase of the SLC pixels is proportional to the slant range at closest approach of the SAR to the point whereas in the Doppler centroid convention the phase is proportional to range at the center of the synthetic aperture reference function. In the reference function center phase convention the range spectrum is centered about DC in the SLC image. The GAMMA MSP produces SLC images using the ref. center phase convention.

It is possible as an option to write out the SLC data after common band filtering in range and azimuth. For offset tracking purposes (e.g. glacier motion) using the filtered data may improve the error in the offset measurements. A SLC parameter file is produced for each of the common-band filtered output SLC data files. The file names for the filtered data and parameter files are entered on the command line.