Hello everyone, I am a new user of sentinel-1. Now I’m doing my ship detection project and I want to distinguish the backscatter value from the sea and from the ship. does anyone know how to calculate or show the backscatter value of Sentinel-1? 
Calibration will give you the backscatter-coefficient Sigma_0. In addition you should perform S-1 Thermal Noise Removal. If you are only interested in targets on the water Ellipsoid Correction is enough for geolocation.
hi mengdahl, thank you for the response
actually I still don’t really understand about some tools in SNAP. What is Ellipsoid Correction? is it a part of radiometric or geometric? If i use Ellipsoid Correction then, should i use the Calibration too?
Radiometry corrects the pixel values and geometry their location so yes, you should do both.