Want to find out sub soil moisture from Sentinel or any other satellite images. But don't know the process exactly.
If you are interested into some global soil moisture products, I'd advice to see what is doing the research group lead by Wolfgang Wagner in TUWien, which is a world-leading research group in soil moisture products from remote sensing. This page is a gateway for 3 different products:
Metop ASCAT Soil Moisture
ESA CCI Soil Moisture
The ESA-CCI soil moisture product (daily global soil moisture data) can be downloaded from this page after completing a form.
- ASAR 1km Surface Soil Moisture
If you want to know how soil moisture can be retrieved from remote sensing, it is actually a quite long process and it depends a lot of what you are interested in (passive vs active sensors, time & spatial resolution, depth of characterization). I'd suggest the following review article, although many other are available:
- Wagner, W., Blöschl, G., Pampaloni, P., Calvet, J. C., Bizzarri, B., Wigneron, J. P., & Kerr, Y. (2007). Operational readiness of microwave remote sensing of soil moisture for hydrologic applications. Hydrology Research, 38(1), 1-20.
Note: I'm not involved at all in the Wagner research group. Other research group worldwide and publications are surely worth considering.