COSMO quad-pol preprocessing with SNAP


I need to process CSG quad-pol data, do calibration, terrain correction and reprojection. For that, I think I need to bring together the four polarimetric channels into 1 product in SNAP. Does anybody have experience how that works?

My goal is to generate the coherency matrix elements

I tried to do calibration, terrain correction and reprojection with the individual channels:

but it does not work at all (the outcome is a grey intensity image).

Ellipsoid correction instead of terrain correction works, but SNAP loses the complex numbers on the way and produces only the intensity.

Kindly, pedro