I have read articles about the use of radar information to quantify soil moisture (like Sentinel1), is there any combination of bands (according to the polymetry) that allows me to clearly see my target?
The short answer is - there is no general polarization or band combination which lets you directly estimate soil moisture from backscatter, because too many factors play a role.
Have you seen this FAQ? I want to extract soil moisture from SAR data
Thanks for the reply, it clears up a lot of my doubts.
Anyway, would it be possible to combine different polarizations of more than one satellite?
Yes, this is possible. Not in a way that coherent (polarimetric) scattering between two independent acquisitions is preserved but different satellites can still contain complementary information. We tested this here for land cover classification Remote Sensing | Free Full-Text | Refugee Camp Monitoring and Environmental Change Assessment of Kutupalong, Bangladesh, Based on Radar Imagery of Sentinel-1 and ALOS-2