UAVSAR backscattering coefficient extraction in dB

I’m new with remote sensing polarimetry data processing. I had processed *.grd format of UAVSAR data and I would like to extract scattering coefficient in dB. does BMP format give me backscattering coefficient?how can I see backscattering coefficient for each pixel?

BMP is just the data format, not necessarily related to the type of information contained in the products. After importing, most of the SAR data is uncalibrated.
If you want the backscattering coefficient, you need to calibrate your data. But note that after calibration you can no longer apply most of the polarimetric tools, because they require the complex information.

Edit: Why not continuing here? soil moisture mapping using UAVSAR