"I have an additional question. As the manual says：“In case of 2 sensors analysis, two different Refl Maps are processed and saved. They are called respectively MeanFirst and MeanSecond”.
In case of different sensors, is it possible to generate only 1 mean amplitude image for the common AOI？ How to do it ?"
The case of 2 sensors analysis is an advanced processing mode (as ERS and Envisat combination) that does not apply to your case.
You get only one reflectivity map per dataset.
If you are talking about combining different datasets (as ascending and descending tracks or different sensors) you can combine the geocoded (or orthorectified) maps in Google Earth or in a GIS environment.