TopSAR coregistration questions (help!)

Hi everyone,

I would like to know something about S1 SLC IW products coregistration.

  1. after the TOP-Split operation for two products ,coming one from ascending orbit and the other from descending, is it possible to execute a back-geocoding coregistration? The back-geocoding seems to be possible only between subswaths with same numbers (1-1, 2-2…)

  2. the orbit type (ascending or descending )is visible only in the metadata and product properties,or even before downloading a s1 product?

3)for a coregistration of 3 s1 products and after TOP-merge and terrain correction I had an enormous processing time with 32GB of Ram,is that “normal”?
Questions especially for @lveci and @ABraun :slight_smile:

Thanks in advance!

Don’t attempt to coregister ascending and descending orbits. Remember that shadow and layover fall into opposite directions.
Upon ordering the data you can specify ascending or descending orbits in the SciHub.
Always search for data coming from the same orbit (relative orbit number can be calculated from the absolute orbit number. see Sentinel 1 relative orbit from filename)

Yes,and then also the subswaths with same indexes belong to different regions if the products are in descending & ascending orbit respectively. So an attempt of coregistration could return an empty product, is that wrong?
Then to create a stack o multiple coregistered images (with same polarization) should I select only products from the same orbit and in different times?

yes, exactly. Stay in the same relative orbit. All ascendings or all descendings. You can create two stacks, analyse separately, create separate thematic maps and fuse the results, if your please.

And what about the processing time? could that be caused by the length of the processing chain? probably also @marpet could know the answer :slight_smile:

I am also experiencing long processing times, even though I am just working with IW SLC pairs to obtain amplitude change detection and coherence components (both geocoded). My machine has also 32 Gb RAM. I am trying to avoid working on anything else which consumes a lot of RAM. I would do any Office stuff or browsing on a separate machine.

Try not to do everything in a single monster graph, that tends to be inefficient, especially on machines what do not have SSD:s.