Hello Fabio.

I attach linñ below a document about sentinel-1. I think it is very important to solve your problema.

Also you can obtain information or data (with Landsat 8) of your study área in:

http://landsatappv1p1.s3-website-us-west-2.amazonaws.com/

Enjoy.

Emilio Ramírez Juidías.

http://www.itc.nl/library/papers_2016/msc/wrem/cliu.pdf

as Sentinel-1 uses a c-band radar with a wavelength of about 5 cm it only interacts with the canopy or surface of vegetation. Some results can be derived about the abundancy of several types of vegetation but for real biomass estimation you would rather need ALOS PALSAR which uses L-band data. It is highly sensitive to aboveground biomass between 0 and 350 t/ha.

Here is a nice study for savanna landscapes:

http://www.geos.ed.ac.uk/homes/cryan/pubs/Mitchard2009GRL.pdf

You can get some of the ALOS data for free at the ASF:

https://vertex.daac.asf.alaska.edu/

JAXA also provides yearly mosaics of ALOS data for free:

http://www.eorc.jaxa.jp/ALOS/en/palsar_fnf/fnf_index.htm

Both require a short registration.

https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/applications/land-monitoring