ANSI-C program: SLC_diff_intf.c
NAME
SLC_diff_intf - Multi-look complex interferogram
generation from coregistered SLC data and a simulated
interferogram derived from a DEM.
SYNOPSIS
SLC_diff_intf <SLC-1> <SLC-2R>
<SLC-1.par> <SLC-2R.par> <OFF_par>
<interf> <rlks> <azlks> [loff] [nlines]
[sps_flg] [azf_flg] [rbw_min] [rp1_flg] [rp2_flg]
| <SLC-1> | (input) single-look complex image 1 (reference) |
| <SLC-2R> | (input) single-look complex image 2 coregistered to SLC-1 |
| <SLC1_par> | (input) SLC-1 ISP image parameter file |
| <SLC2R_par> | (input) single-look complex image 2 coregistered to SLC-1 |
| <OFF_par> | (input) ISP offset/interferogram parameter file |
| <sim_unw> | (input) simulated unflattened and unwrapped interferogram, same range and azimuth looks and dimensions as the output interferogram (float) |
| <diff_int> | (output) differential interferogram (fcomplex) |
| <rlks> | number of range looks for the output interferogram |
| <azlks> | number of azimuth looks for the simulated and output interferogram |
| [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 |
| [rbw_min] | minimum range bandwidth fraction (0.1 --> 1.0)(default: 0.250) |
| [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) |
EXAMPLE
SLC_diff_intf 19960421.rslc 19960422.rslc 19960421.rslc.par 19960422.rslc.par 19960421_19960422.off 19960421_19960422.sim_unw 19960421_19960422_sps.diff
1 5 1 1
DESCRIPTION
SLC_diff_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 a simulated unwrapped interferogram
and computes the differential 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 unwrapped phase provided in the sim_unw file is subtracted from the SLC data prior to generation of the interferogram, and hence prevents undersampling of the final interferogram. The simulated interferometric phase data must have the same sample spacing and dimensions as the output interferogram. This means that when the ISP offset parameter file is created using the ISP program create_offset , the number of range and azimuth looks in the output interferogram must be specified on the command line. This leads to significanlty higher correlation for scenes with larger baseline and significant topographry.
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 diff_int file.
Range spectrum filtering is applied using the sps_flg command line option. This filtering accounts for the shift of the ground reflectivity spectrum induced by the difference in incidence angles between SLC-2 and SLC-1. Only the range spectrum interval common to the the two SLC images is retained. No multi-look intensity images are produced from the two SLC images by SLC_diff_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.
The user also has the option to apply azimuth common-band filtering. The SLCs may have been acquired with different Doppler centroids. This filtering step improves the correlation by preserving on the common azimuth spectrum of the SLCs prior to generating the inteferogram.
The recommended approach for resampling the SLCs to coregister the data 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.
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 interfeormetric 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.
SEE ALSO
SLC_interp_lt, rdc_trans.