Export data from Sentinel 1 to GeoTIFF


Good Morning! I am dealing with GRD images of Sentinel 1, to extract the coefficient of backscatter, to measure soil moisture.
First I get data from Sigma0 VH_dB = -31,661 to -1,661 and Sigma0_VV_dB = -24,016 to 7,306. Are they normal values?
And another thing, when it comes to exporting it to GeoTIFF and opening the file in ArcMap, I get totally different values, why is that?
Thank you very much for the help