Removing a Deformation Model Using ROI_PAC
ROI_PAC provides the ability to remove a deformation model from an image pair during processing. Both an interseismic deformation model and a coseismic model may be removed during the course of processing. This tutorial provides details on how to prepare your deformation model for incorporation into ROI_PAC.
Preparing the Model
I will assume that you have already calculated your deformation model and have it in an ASCII format separated by white space. If your file has the format:
x y e n u
where x and y may be in UTM or longitude and latitude (WGS84). Additionally, the deformation values e, n, and u are in meters. Once you have your deformation model, the goal is to create three 4*real binary files, one for each deformation component, East, North, and Up and their associated resource files (.rsc files). The deformation file names must end in either an E, N, or U depending on which component they contain. While the resource files must have the same form as the resource file for the DEM. If your DEM projection is UTM then your deformation files need to be in UTM, but if your DEM is in latitude and longitude, then your deformation model needs to be in latitude and longitude as well.
I find it easier to calculate deformation models in UTM however, my DEM's are often in latitude and longitude. Thus, it is necessary to convert the UTM deformation model from UTM to latitude and longitude. To do so, one can use either PROJ or GMT to convert the UTM coordinates to latitude and longitude.
As an example, I've included this script to take a deformation model in UTM with the same format as discussed above and create three input binary files and their associated resource files (.rsc) for input to ROI_PAC. This script requires both PROJ and GMT to be installed.
Running ROI_PAC
Once you have your three binary deformation files along with their resource files, you need to tell ROI_PAC where you have put them. I typically place the three binary deformation files --- for example purposes, lets call them 081202-090106E, 081202-090106N, and 081202-090106U --- along with their resource files in a subdirectory inside my processing directory. If your processing directory were,
/home/user/data/InSAR/081202-090106
you could create a directory inside the processing directory called coseismic and add the following line to your .proc file where 081202-090106 is the prefix of my three deformation files, 081202-090106E, 081202-090106N, and 081202-090106U.
CO_MODEL=/home/user/data/InSAR/081202-090106/coseismic/081202-090106
It's also possible to remove an interseismic deformation model by following the same proceedure and specifying the file name prefix in your .proc file as follows:
INTER_MODEL=/home/user/data/InSAR/081202-090106/interseismic/081202-090106
Once you've added these extra lines to your .proc file, run process_2pass.pl as usual.
ROI_PAC's Output
Once your process_2pass.pl run has completed, you should have geo-coded interferograms with your deformation model subtracted.
The output file names from the ROI_PAC run will contain the string -models as part of their file name indicating that they have the model subtracted from them. For example, if we were taking 4 range looks, our final geo-coded output file from a ROI_PAC run that subtracted our deformation file would be:
geo_081202-090106-models_4rlks.unw
Wrapped output created before the deformation model is subtracted should exist in the output directory as well. This allows you to compare the removal of the model with the original interferogram. Using the same example as above, we would also have a file called:
filt_081202-090106-sim_HDR_4rlks.int
Which would contain the complex, filtered interferogram with orbit-estimated baseline correction performed and averaged with 4 range looks. It is possible, though not fully automated, to unwrap this file and geo-code it for comparison to the file created with your deformation model removed.
Tips
- Don't forget, byte-order counts. Make sure you generate your binary deformation files on the same architecture on which you'll be processing your InSAR data.
- Make sure your DEM and your deformation models use the same projection (i.e. UTM or LATLON in the resource file).
- The attached script creates binary deformation files with a 90 m pixel spacing. This isn't strictly necessary if you have a smooth deformation field, 300-500 meter pixel spacing should be sufficient.
- There are problems with removing co-seismic models from the script process_2pass_master.pl when using the snaphu unwrapping method. The details need to be worked out, but it is appears to be a scripting issue and so should be a straightforward fix.