Geocoding ALOS polarimetric decomposition products

Hi all,

I’ve read the tutorial on orthorectifying ALOS data. From what I can see there is a step of simulating a SAR image and matching it to the actual data. How can I apply the output GCPs to a derived product? I’m specifically working with a polarimetric decomposition generated from ALOS1 L1.1 data. Note the decomposition is a multi-looked version of the original dataset.



Edit: the post contains wrong information and is therefore no longer of use. The problem is solved by @lveci below.

the matching in the SARSim Terrain Correction is performed automatically.

How did you generate the multi-looked polarimetric decomposition? To my understanding, polarimetric information is lost when applying multi-looking. So you must have applied it after the decomposition? T

The SAR Simulation Terrain Correction simulates a SAR image from the scene geometry and a DEM and then tries to coregister it with the SAR image using cross-correlation. If your working on a decomposition, this won’t work. You’ll need to use the range Doppler terrain correction. With ALOS 1.1 there may still be some error in the geocoding unless you can correct the orbits.

The multilooking can be applied to quad pol data and produce complex output. You can then do the polarimetric processing as usual.

I didn’t know that, thanks for clarification.

Thank you @ABraun and @lveci for your inputs
I understand the co-registration is made with the amplitude information. Is it possible to save the ground control points generated at this step, and apply them to geocode the polarimetric decomposition? I tried the range doppler terrain correction, and as you noted, there were still geocoding errors.
Thank you again!

the GCPs are randomly generated but you won’t find ones which match when you input the decomposition and match it to the simulated SAR image as lveci said. So they wouldn’t contain information which can be used for geocoding.

Which error appears when you try to use the RD-Terrain correction? Where is your study area located?

The GCPs cannot be generated with the decomposition. Once they are generated from amplitude data they are mere tie points which can be applied to geocode any image with the same geometry as the amplitude data. The question (for @lveci) is whether SNAP provides this functionality.

No, SNAP can’t do this at the moment but, I agree it would be useful for this situation.

OK, thank you anyway to both of you for the clarification!