Hi, I want to create a difference image from two multi-temporal S1 GRD IW subset products.
After Doppler Terrain Correction, I presume I still need to coregister the two images for accurate differencing. However, I find the Coregistration dialog confusing, and the ‘Help’ pages imply that coregistration is only used for InSAR purposes. Can someone please give me some advice? Do I need to coregister, and what parameters should I set in the coregistration dialog?
Many thanks for any help
Don’t let all the parameters confuse you. Throughout SNAP it’s intended that the defaults should work for most cases and the parameters are there for extra control.
If the GRDs are for the same orbital pass and relative orbit then terrain correcting and create stack may be enough to get pixel level alignment.
Many thanks for your kind reply. However, not all defaults are given, i.e. the type of re-sampling to be used?
Could you please still answer my other question, i.e.
“I presume I still need to coregister the two images for accurate differencing.” Is this right as the Help pages infer only to use for InSAR?
Also, In mountainous areas, is it better to do differencing without terrain correction?
Many thanks for any further advice.
For info I am trying to create a difference image over the island of Dominica pre- and post- hurricane Maria (18 Sep 2017) using Sentinel-1 GRD products.
My processing steps are:
1: Extract sub-scene
2: Apply radiometric calibration
3: Apply Doppler terrain correction
4: Coregister the image pair
5: Band maths to subtract one form the other
Besides my query above on coregistration, I also ask should I be applying a despeckle algorithm somewhere, or is it best to not despeckle if differencing?
For information, I am differencing a scene dated 25 Aug 2017 from 18 Sep 2017 (the latter being the actual date of the hurricane). Basically, nothing is the same in the resulting difference image!
Many thanks again for any information.