no, they are the same measurement. But it would be good to calibrate the data before analyzing it. Please have a look at this topic: Radiometric & Geometric Correction Workflow
Retrieval of soil moisture with SAR is surely challenging. Based on your previous questions I can suggest to read some of the basics on radar processing (or have a look at the tutorials of ESA or ASF) before getting into soil moisture retrieval so you have a better understanding about what you are doing. There is no standardized solution on how to derive soil moisture and you surely need data collected in the field to calibrate your prediciton.