TOPSAR coregistration algorithm

Hi all, I want to do some modification to the source code of SNAP for my own research use, I would like to know if there are any references or documents which explain the coregistration(back geocoding) algorithm implemented in SNAP? And the implementions of other algorithms like interferogram or StampsExport can also be helpful.

I think the attached file will help you.
Sentinel1_TOPScoregistration.pdf (2.9 MB)