Raster merge

In the context of Oil Spill detection, I have an AOI which is situated on the border of two sentinel-1 tiles. I need therefore to merge the two tiles and then crop out the window containing the whole AOI.

As I also need to preprocess the data I wonder which order is more effective (and why?) :

  1. Preprocess of individual tiles → merge the two tiles → Crop out the interresting window

  2. Merge the two tiles → preprocess the new mosaic → crop the interesting window