ANSI-C program: gc_insar.c
NAMESYNOPSIS
gc_insar <SLC_par> <ISP_par>
<hgt> <DEM_par>
<lookup_table>
| <SLC_par> | (input) SLC parameter file (reference geometry) |
| <ISP_par> | (input) ISP parameter file |
| <hgt> | (input) height map in SAR coordinates (float) |
| <DEM_par> | (input) DEM parameter file defining region of the output map |
| <lookup_table> | (output) geocoding lookup table in SAR geometry (containing corresponding map coordinates) (fcomplex) |
EXAMPLE
gc_insar 19960421.par 19960421_19960422.off
19960421_19969422.hgt dv.utm.par
8560_8059.rdc_to_utm
Creates geocoding lookup table based on height map in SAR geometry (which was derived with SAR interferometry).
DESCRIPTION
gc_insar calculates a
complex valued transformation lookup table for terrain corrected
geocoding. The calculation is based on heights in (range-Doppler)
SAR coordinates (as retrieved from SAR interferometry).
The transformation lookup table describes the geometric transformation between images in SAR (range-Doppler) coordinates and a map projection. The complex valued lookup table has the dimension of the images in the SAR coordinates. Each complex value contains the corresponding map coordinates with the real part corresponding to the real valued column (corresponding to easting or longitude) and the imaginary part corresponding to the real valued row number (corresponding to northing or latitude).
The SAR image geometry is defined by the SLC parameter file and the ISP/offset parameter file. The map projection is defined in the DEM/MAP parameter file which can be created using the program create_dem_par. The DEM_par defines the map projection, corner coordinates, posting, and map dimensions in northing and easting.
The input height map used is typically derived from the unwrapped phase SAR interferogram. For data gaps (i.e. pixels with NULL height value, which is 0.0) the transformation value is set to (0.0, 0.0). The forward and backward geocoding programs identify these negative row and column numbers as NO-DATA. The consequence of such gaps is an increased spacing of the valid data points used in the resampling and interpolation steps.
Notice that the geocoding lookup table calculated is based on the available SAR geometry information. In particular the orbit data is often not perfectly accurate, so that application of a fine registration step is recommended.
Unlike gc_map no additional parameters such as local incidence angle, projection angle (for pixel size normalization), pixel size normalization factor, zenith and orientation angle for local surface normal, layover/shadow map is calculated from the height map and SAR geometry are calculated.
The geocoding lookup table is used by the programs geocode and geocode_back for forward and backward geocoding. The geocoding lookup table may be inverted using the program gc_map_inversion.
For the generation of Geocoded Ellipsoid Corrected (GEC) products the program gec_map with a constant height value specified instead of the input DEM file can be used. GEC geocoding does not require height information other than the constant height value.
SEE ALSO
geocode, geocode_back, gc_map_fine, init_offsetm, offset_pwrm, gc_map_inversion, gc_map, gec_map,
typedef_ISP.h, typedef_DIFF.h .