Offset Tracking (Greenland) - ACE30 vs new Copernicus 30 m DEM

Hello everyone!
I am working with GRD products from Sentinel-1 to calculate glaciers velocity in Greenland. So far I have used ACE30 DEM for DEM-assisted coregistration step and everything worked fine. Recently I’ve changed DEM to new Copernicus 30m DEM. Now I receive totally different results (previous velocities were comparable with MEaSUREs data) and I am not sure what is the reason.

Moreover, I’ve another pair of GRD images: from different satellite mission (same area, same dates) and in this case Copernicus DEM gives the best results - and they agree with results from S1 data with ACE30 DEM. Applying ACE30 gives far to high velocities (over 120 m/day - quite impossible).

Some ideas what is the reason of such differences? Why one DEM gives great results, when the other one is totally wrong? And why 1 DEM works great with S1 data and for different satellite another one is much better (area and timspan are the same so that’s not the problem)?

have you ever dispalyed the ACE30 DEM and Copernicus 30m DEM side by side within your area? I’m not sure how this immense differnce in spatial resolution affects the coregistration accuracy, but maybe @qglaude has an idea.

The DEM precision shouldn’t have a huge impact. The DEM is used only for the coregistration but in theory not even mandatory. However, large differences in the DEMs (data gaps, resampling errors) may lead to bad coregistration.

I would advise to look at the DEM difference, as @ABraun suggests.

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Thanks for your comments, I will take a closer look at both DEM.

But I am still not sure why for the same area but different satellite missions: one DEM works when the other doesn’t for S1 data and for the other dataset ir works quite the opposite.