Sentinel-1 A- extracted DEM

Hi, I am extracting DEM from Sentinel-1 A data, but the vertical accuracy of the extracted DEM is very low to the limit that I can find differences in elevations reach 300 meters between the extracted DEM and SRTM 1" DEM. Does anyone know why or a solution?

In general S-1 is not recommended for DEM creation ,But in case S-1 is the only available solution, please put in mind the points are mentioned in the following post,

Selecting Images for InSAR DEM generation, Source of the post

It’s incomparable between S-1 created DEM and SRTM1 for the reasons are mentioned in the following post,

Incomparable DEM resulted from S-1 pair and SRTM, Source of the post

Thanks a lot.