Gamma DIFF&GEO: Reference Manual

gec_map

ANSI-C program: gec_map.c, gec_map_grd.c

NAME
gec_map - Geocoding lookup table derivation for ellipsoid corrected geocoding.
gec_map_grd - Geocoding lookup table derivation for ellipsoid corrected geocoding of SAR image in ground-range / azimuth coordinates.

SYNOPSIS
gec_map <SLC_par> <OFF_par> <DEM/MAP_par> <href> <DEM/MAP_seg_par> <lookup_table> [lat_ovr] [lon_ovr] [sim_sar] [u] [v] [inc] [psi] [pix] [ls_map]

<SLC_par>	(input) ISP SLC or MLI image parameter file (slant range geometry)
<ISP_par>	(input) ISP/offset parameter file, enter - if geocoding SLC or MLI data
<DEM_par>	(input) DEM parameter file
<href>	(input) elevation reference [m]
<DEM_seg_par>	DEM/MAP segment parameters used for geocoding If this file exists, then the bounds of the DEM segment used for geocoding are read from the parameter file, otherwise the bounds are estimated using the SLC parameters and state vectors, and written to the new parameter file
<lookup_table>	(output) geocoding lookup table
[lat_ovr]	latitude DEM oversampling factor (default=2.0)
[lon_ovr]	longitude DEM oversampling factor (default=2.0)

Remark: enter - as filename to avoid creation of corresponding output file

EXAMPLE
gec_map 8560.slc.par 8560_8059.off dv_utm.par 400.0 8560_8059.utm.par 8560_8059.utm_to_rdc 2 2

Creates geocoding lookup table based for ellipsoid corrected geocoding (oversampling factors in latitude and longitude 2.0, a reference elevation of 400.0 m is used).

gec_map_grd 8560.grd.par dv_utm.par 400.0 8560.utm.par 8560.utm_to_grd 2 2

Creates geocoding lookup table based for ellipsoid corrected geocoding (oversampling factors in latitude and longitude 2.0, a reference elevation of 400.0 m is used).

INSTALLATION
Source code gec_map.c and gec_map_grd.c in ./src. For compilation adjust and use Makefile: Executable versions gec_map and gec_map_grd in ../bin

AVAILABILITY
Uses ISP and DIFF type definition files typedef_ISP.h, typedef_DIFF.h.

DESCRIPTION
gec_map calculates complex valued geocoding lookup table based on the MAP projection and the SAR imaging geometry. The geocoding lookup table has the dimension of the DEM/MAP segment and contains the corresponding SAR coordinates as complex valued numbers with the real part corresponding to the real valued column and the imaginary part corresponding to the real valued row number.

If the interferogram/offset parameter file is not available because geocoding is desired of an image not related to an interferogram, such as an MLI image from a SAR processor, a - may be entered instead of the parameter file name. In this case the required parameters are extracted from the SLC/MLI parameter file. The program create_diff_par can then be used to create the DIFF/GEO parameter file used to measure offsets between a simulated SAR image and the actual image in order to correct the geocoding map produced by gec_map.

A DEM/MAP segment covering the area of the SAR image is determined from the input DEM/MAP parameter file which may cover a much larger area than covered by the SAR data. The indicated oversampling rates in range and azimuth are also considered in the definition of the output DEM/MAP parameter file (by modifying the map pixel spacing, and number of pixels necessary to cover the SAR data). This allows to generate geocoded products at user defined spatial resolution.

Notice that the geocoding lookup table calculated is based on the map projection and SAR geometry information. In particular the orbit data is usually not perfectly accurate. 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 gec_map_inversion.

gec_map_grd has the same functionality as gec_map, but for SAR images in ground-range / azimuth coordinates (instead of slant-range / azimuth). No ISP/offset parameter file is asked for on the command line.

OPTIONS
The following DEM/MAP projections are supported:

Keyword	Projection
EQA	Equiangular
UTM	Universal Transverse Mercator
TM	Transverse Mercator (Germany, Finland, Italy, and others)
OMCH	Oblique Mercator (Switzerland)
LCC	Lambert Conformal Conic (France)
PS	Polar Stereographic
SCH	SAR Coordinates used at JPL
PC	Polyconic Projection
AEAC	Albers Equal Area Conic

For Terrain Corrected Geocoding based on a DEM provided in map geometry the programs gc_map and gc_map_grd can be used.

For Terrain Corrected Geocoding (GTC) based on height information given in SAR range-Doppler coordinates (typically estimated using SAR interferometry) the program gc_insar can be used.