I tried to coregister the IW2 sub-swath of Sentinel-1 IW SLC TOPSAR data with another IW2 sub-swath of a Sentinel-1 TOPSAR product which is a S1 TOPS Slice Assembly product, using the S1 TOPSAR Coregistration operator and I got the error ‘ raf == null!’. What could be reason for this error?
Is there any solution to avoid this error and to do a successful coregistration of TOPSAR Slice Assembly product with another TOPSAR data using S1 TOPSAR Coregistration operator?
Are the products compatible, i.e. from the same orbit-track?
Yes, the products are compatible, of the same track, but of different orbits as the scenes are of different dates. I could do TOPSAR corregistration with one pair and make interferograms, topophase removal, phase filtering and SNAPHU unwrapping etc. Slice Assembly was performed as the interested areas are situated in two scenes of the same track and orbit (acquired on the same date).
I’ve seen this problem recently when you have a dimap file and the subset operator. Do you have the slice assembled product saved in dimap and then you have the TOPSAR coregistration graph? The first operator in the graph is TOPSAR split which passes the data through without manipulation but I think the band names change. @marpet this could be another scenario where issue SNAP-516 appears.
Thanks for your reply. I do have the slice assembled product in dimap format. I did not use the subset operator.
The TOPSAR data sets I used are the following:
Slice assembly was performed on the TOPSAR data sets acquired on 9 Oct 2015 and later I tried to coregister Slice Assembly product with the TOPSAR data acquired on 8 Dec 2015 using TOPSAR coregistration tool in SNAP and got the error of ‘ raf == null!’. Is there any solution for this error?
Instead of using TOPSAR Coregistration, should I try using the S1-Deburst operator on the SAR scenes and apply the normal Radar Coregistration operator for making an interferogram for the full scene area? I can do a subsetting also if needed before making inteferogram (for faster processing).
I could find a solution to avoid getting the error of ‘ raf == null!’ while performing TOPSAR Coregistration by selecting the following options in the S1 TOPS Coregistration (TOPSAR Coregistration) Operator : Data Format as ‘BEAM-DIMAP’ (instead of selecting ‘Any Format’ which is default) the in the first Tab ‘Read’ for the Master scene (as I used TOPS Slice Assembly product of SNAP) and selecting Data Format as ‘Sentinel-1’ in the second Tab Read (2) for the Slave image -Sentinel-1 scene- I used… It is working now with these options selected for the data used.