GAMMA Questions

I've found it to be somewhat challenging, as there are some ramps that still show up in the data, but it does work well overall. I'd be happy to share my routines for that if it would be helpful. (Mike Poland)

Hi Mike,

I also face the problem that I have overall ramps left at the end of the processing, besides applying quad_fit and quad_sub that should actually remove these ramps (at least to my understanding). My current solution is to use SRTM data to de-ramp the final result, whereas I have masked out the glaciated areas during the ramp calculation.

I also tried to use IceSAT data as proposed in the article by C. Nuth and A. Kääb. However, there is no good coverage within my region of interest (Central Asia) and the remaining IceSAT footprints have in some areas (steep slopes) sometimes incredible high differences to the SRTM DEM (up to 1000 m!). So I think I will not use IceSAT at all, but only fit the TDX DEMs to the SRTM DEM.

What's your solution to remove the ramps?

This is similar to the solution I use. I employ a high-res DEM to de-ramp the final product, but it takes a few steps and involves using the DEM to first refine the baseline:

1) add the topo phase back into the unwrapped image (sub_phase)
2) extract GCPs using the DEM and calculate their phase values (extract_gcp and gcp_phase)
3) recalculate the baseline (base_ls), resimulate the topo phase (phase_sim), and re-remove that phase from the unwrapped image (sub_phase)
4) calculate and subtract a quadratic to remove any residual, which often still exists after the baseline refinement (quad_fit and quad_sub)

The interferogram should be flat at this point, except for any difference in topography since acquisition of the TDX data. You can use all of the calculated baseline information to reprocess the scene, and it should be in good shape.

Hi Mike,

thanks for the suggestion. I'll give it a go the next time I work with TDX DEM generation. :)

Hi all.
After seeing the suggestions from everyone of you. I would like to add one thing. If the SRTM Heights are added back to the TDX DEM in order to de-ramp it, this will generate penetration bias due to C band + X band both. This is a problem in case if anyone concerned with absolute DEM but if you are most likely to get elevation changes wrt SRTM DEM, C band penetration is removed again. I would rather try to independently process the TDX data (Differential Interferogram with 0 height) to get rid of these different penetration biases. It may work !
Thanks