Gap in two S1A adjacent images of same day and same relative orbit!

Hello all,

So I am preprocessing some S1 GRD data downloaded from the ASF mirror.
I used both pyroSAR and SNAP s1tbx to process the data but I am getting a gap of approximately one pixel in between the two images (See images to see what I mean) I tried both with and without border noise removal without any success of a proper gapless mosaic of the two images.

Does any of you have any idea where or what I might be doing wrong??

Any help and suggestions are



I seemed to fix the gap issues with slice assembly but now there is another problem. Now the two images joined perfectly without any gap but there is a huge shift in the images by at least 200m.

It turns out I made the mistake of using external dem which did not fully cover the AOI, That’s why there was the shift. Now everything is fine. Hope this helps anyone facing the same problem!