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precise geocoding refinement
Added by Justin Brandt over 7 years ago
Hello InSAR world,
I'm working on processing some TSX data in Southern California looking at subsidence, and I seem to be having trouble with the geocoding refinement. All my images seem to be shifted to the East about 50 or so meters. Overlaying my interferograms on street shapefiles or aerial imagery show the offset is pretty obvious.
I've used both a USGS 10m NED dem and a LiDAR dem provided by a local agency, both appear to have the same offset.
I'm essentially using the scripts from the 2PASS_INT script included in the GAMMA package (gc_map, offset_pwrm, offset_fitm, gc_map_fine). I've been able to successfully process many other data types (ERS1/2, ENVISAT, ALOS1/2, CosmoSkyMed, Sentinel 1A), but for some reason the TSX geocoding is escaping me. I tried using pixel_area
I'm hoping someone has an example of a script they're working with that has been successful for them.
Replies (3)
precise geocoding refinement - Added by Charles Werner over 7 years ago
Hello,
The DEM must be referenced to the WGS84 ellipsoid. I suggest that you use the
mk_geo_radcal script for geocoding and calculation of the DEM in radar
coordinates, rather than the older csh scripts. With mk_geo_radcal you should
use the -d (generate the dem resampled to slant range) -p (use pixel_area to
simulate the image) and -j (ignore layover-shadow map) options.
TSX data have very accurate state vectors and the refinement is very small. I
suspect your error is due to using the wrong ellipsoid for the DEM. You need to
change the reference ellipsoid for the data for example with dem_trans.
Best regards,
Charles
RE: precise geocoding refinement - Added by Justin Brandt over 7 years ago
Hi Charles,
I have a quick question about dem_trans.
The DEM I have for this area is an airborne LiDAR dem supplied by a cooperator. The original datum/projection was a state coordinate system with data values in feet, so using ArcGIS I translated it to a UTM Zone 11 (NAD83) projection (values still feet). I will use dem_trans to convert it to the EQA WGS84 required by GAMMA.
I have a question about the dem_par files used as input/output for dem_trans. Since my LiDAR dem values are in feet, I planned to use a DEM_scale of 0.3048 for the DEM2_par to convert to meters, but it looks like dem_trans won't allow a DEM_scale other than 1.000.
Should I just edit the DEM2_par file after I run dem_trans, so that DEM_scale = 0.3048?
Thanks
RE: precise geocoding refinement - Added by Charles Werner over 7 years ago
Hello,
The option to convert the input DEM data from feet to meters was not included in
the dem_trans dem_trans requires that the input heights are provided in meters
so that vertical datum shifts are correctly calculated.
Here are two options:
1. Get ArcGIS to translate to meters by applying a scaling
2. Use one of the Gamma programs float_math or lin_comb to scale the data. Note
that the Gamma software requires the data to be in big endian format. If you are
in little endian format, you can convert to big endian using the gamma program
swap_bytes.
Best regards,
Charles