How to calculate the Scattering Matrix for a Sentinel-1 image

How can we calculate the elements of thescattering matrix(Spqwithpandqbeing the transmit/receive polarizations), for aSentinel-1image?

Does the image have to be in aSingle-Look Complex (SLC)format (contains complex values), in order to calculate thescattering matrix?

I found the formulas that I was looking for in this article:

These formulas obviously depend on thefresnel reflection coefficientswhich can be found here: