I’m a Masters Student a bit new to this, and I’m using the S1tbx to calibrate an image I have. It is a GRD IW Sentinel-1A product. The purpose is to prove that by doing this manually I can get the same result as the inbuilt automatic calibration tool as part of the project. I know that in ENVI the Band Maths option can be used to calibrate an image using the formula provided in documentation. I was wondering whether this was also an option on SNAP, or if not what to use?
I have used the formula in https://sentinel.esa.int/documents/247904/685163/S1-Radiometric-Calibration-V1.0.pdf for a distributed target and obtained a sigma0 value of around 571. When trying to use this figure in the Band Maths window expression box I have been using expressions like “Amplitude_VV*571.4289793” and “Amplitude_VV^2/(6.6117035e02)^2”. I am not sure of the correct usage of the number now that I have worked it out, and none of the outputted bands look any different to the original. When I look at the pixel info for corresponding pixels across the images, on the outputted bands it lists under the “Bands” tab the corresponding values between images, and although the values displayed are orders of magnitude different, they don’t physically look different on the image produced. I was wondering why this might be? They are also a magnitude of 10 out, compared with the automated calibration image.
Firstly, am I going about this the right way using Band Maths? Secondly, is the use of the sigma0 number and the band name in either of the expressions “Amplitude_VV*571.4289793” and “Amplitude_VV^2/(6.6117035e02)^2” correct? Lastly, is the option of “Units” important in the Band Maths window, as I don’t know what to put?
Many thanks for any help,