Is it possible to coregister two S1 TOPS dual-pol images for both polarimetric channels simultaneously?
As far as I know, the “S1 TOPS Coregistration” tool requires the selection of ONE of the polarimetric channels, which is the only one to be coregistered.
From the processing point of view, one channel (preferrably VV for SNR reasons) could be chosen to compute the coregistration shifts, but the two channels (VV and HV) of the slave image could be interpolated by using the same shifts. However, I think this is not supported in SNAP currently.
Yes, it’s not possible with version 3 but, it has been updated just last week. It’s available in the master branch or if you can wait a little while it will be in release 4 later this month.