Terrain Correction Issue with Specific S1 Products

I don’t know if this is the correct place to report this, but I am experiencing an issue when Terrain Correcting two specific GRD products. The resulting output is badly warped near the slice boundary. I haven’t yet experienced this issue with any other dataset, but don’t know if it’s indicative of a wider problem.

The attached image demonstrates the problem scenes (left) against a correct output (right)

The products are:

The minimum repeatable processing steps are:
Slice Assembly > Range-Doppler Terrain Correction (external and SRTM DEMs tested) [Output to Auto UTM]

This effect does not appear when Terrain Correcting each slice independently.

Have you applied the precise orbits?

This effect does not appear when Terrain Correcting each slice independently.

Do you mean that there is no warping? Or that there is no warping and the individual slices are accurately geocoded?

I have not applied precise orbits in this case, but have not seen this problem in any other scene where I have also not applied them.

Most of the output rectifies correctly. The region shown above is an extract near to the slice boundary. The coastline is best at highlighting the warping issue compared to the expected output. The lower part of the scene is really condensed and the middle seems to be stretched out. The problem runs across the whole output.

There also appear to be strips of straight lines running parallel to the angle of the slice boundary (there are two at the bottom and one towards the top of the image above)

I have checked the images and applying precise orbits to the assembled product solves the issue.

My guess is that assembling this particular pair of products creates a set of conditions that make the orbit interpolation step (in TC) go berserk.

As far as I can see the orbit info in the individual products is fine. The problem is in the way SNAP assembles (concatenates) the orbit state vectors or in the orbit interpolation step.

1 Like

Thank you very much for looking into this. Will try applying precise orbits then.