Different velocity results generated from DInSAR and Offset Tracking techniques

Hello everyone,

I am currently working on glacier velocities using SAR interferometry (DInSAR) and offset tracking methods in SNAP. In the DInSAR-based process, I derived a land displacement map and calculated velocities using band maths by dividing displacement values by the time interval between image pairs.

Concurrently, in offset tracking, I employed 10x10 pixels and assumed max velocity of 2 m/day in offset tracking to obtain velocity results.

I calculated the velocity per day using the same method.

The concern arises from the noticeable differences in the velocity values obtained from these two methods. I would greatly appreciate any guidance or suggestions on potential factors that could contribute to these disparities.

Another problem I’m facing is that in the interferometry-based process, the velocity map aligned well with my study area when overlaid with an ESRI shapefile. However, in the offset tracking method (projected or not projected), the velocity map does not align properly with the same shapefile.

Thank you in advance for your time and expertise.