Hello,
We know one single Sentinel-1 swath is quite large. Is it possible to cut a small area out by using SNAP before any SNAP-processing like Gamma0 calculation? Thanks in advance.
Best regards,
Chia-Hsiang Yang
you can import a subset and by this considerably reduce the processing time of the first step you apply.
Select File > Import > SAR Sensors > Sentinel-1
Once you select a valid S1 product, you will see the Subset button on the right
This opens a second window (wait for the preview thumbnail to load) where you can define a subset area by a blue polygon (or entering geographic coordinates)
In the Band Subset tab, you can also select one polarization in case you don’t need both (e.g. for InSAR VV is sufficient)
Confim with OK and a temporary product “subset_0_…” appears in the Product Explorer. You can now apply any processing on it withouth having to process the entire image.
Hello ABraun,
Thanks for your reply. Sorry I might miss some informaiton when I put the quesiton on the table. We’re dealing with IW SLC data. When we followed your step, we hit an error massage saying, quote, “No sub set can be created of a multi-size products.” We want to cut the images as early as possible so we can save some processing time. Do you have any comments on this?
yes, the procedure I suggested above only applies for GRD data. It would have been good to know in advance that you are talking about SLC 
For SLC you can only apply TOPS Split as a first step and reduce the number of bursts as described here.
But as you were referring to the calculation of Gamma0, GRD products are often sufficient.
Appreciate! Really helpful!
Sorry ,I don’t see any preview thunbnail, but "no subset can be create of a multi-size products"after click Subset button,is there something wrong with the step,thanks a lot.
best regards,
boris
Thank you @ABraun,I’ve study your Subsequent answers。Thanks again.
As I explained in the next post, this only works for GRD products: