Coregistration S1, empty images

Microwave Toolbox
#1

Hello together,

I am currently dealing with a large number of S1 - L1 - GRD images and need to continue working with them in R. Therefore it is necessary that I coregistrate them, as R tells me that the extent is (slightly) different. But my problem is, that the coregistration leads to empty images without any information which tool caused the error.

Some technical information:

  • 217 images in total
  • 4 different tracks
  • preprocessing included apply orbit file, calibration, terrain flattening, range doppler terrain correction
  • coregistration settings: nearest neighbour, product geolocation
  • test run with 20 images: for the output extent I tried min (7 out of 20 are nulled), max (4 out of 20), master - find optimal master (6 out of 20)

I know there was a similar post already which suggested that after a preprocessing with terrain correction, a simple stack would be sufficient. But it’s not the case here. As mentioned above, R still indicates that the images of the stack do have different extents.

Does someone has an idea and could explain why this error is occuring? I am fairly new to SAR and snap and would appreciate your help.

Thanks a lot!

#2

if the images were acquired in ascending and descending mode, coregistration might fail because of different topographic effects (despite terrain flattening).
Have you checked if “create stack” produces sufficient results?

Edit: I overlooked that the images are of different tracks, which is the reason for the error.

1 Like
#3

You cannot co-register images from different tracks, except via blind luck in quasi-flat topography.

Co-register each stack separately, then terrain correct them into your projection and pixel-size of choice and then co-locate everything into a single stack (if you wish to have different observation geometries in the same stack).

1 Like
Why the image cannot display after S1-TOPS-Merge?
Intensity SLV file missing in stack after coregistration
#4

Thank you both for your help!

It worked just fine.

I am just wondering if it is of importance to terrain correct them afterwards, or if it´s fine to pre-process them beforehand (Orbit File, Calibration, TF, TC) and then to co-register and co-locate them.
I can´t think of a reason not to do so…