How to get the background noise (NESZ)of sentinel-1

Hello, I want to extract the background noise (db) of the sentinel-1a data. It should be negative, but I don’t get the proper background noise (positive value) in the annotation/calibration noise in the data. What should I do?

You can study the issue by reading this document and its references:

https://sentinels.copernicus.eu/documents/247904/2142675/Thermal-Denoising-of-Products-Generated-by-Sentinel-1-IPF