Real part of the dielectric constant || How to find in Sentinel1

Hi,
Can anyone give me some direction how can the real part of the dielectric constant be found in a soil sample where soil moisture has to be estimated? Is it possible to find it from the amplitude or intensity values of the sentinel 1 image or does it need some sort of laboratory investigation on the soil samples? This is a variable in the Dubois model for surface soil moisture estimation. Thank you …