I’m doing a multitemporal analysis using RADARSAT-1, ENVISAT ASAR WSM, and Sentinel-1A EW data (HH polarization).
I recognize that processing them has a calibration step, but was wondering if there are any established cross-calibration methods I need to use before using the images for my analysis? I thought the calibration step for processing each image was sufficient but wasn’t entirely sure.
Does anyone have any experience with cross-calibration of these sensors? If so, any recommendations on resources so I can teach myself?
doesn’t calibration itself make sure that images of different sensors become comparable?
I agree with @ABraun, performing calibration on all the sensors makes the measurements already comparable. Of course there would be other things to consider, e.g. potentially different incidence angles from the different sensors.
thats right. Calibration to Sigma0 corrects for the overall incidence angle (referring to the flat earth’s surface).
But calibration to Gamma0 (first calibrate to Beta0, then perform radiometric terrain flattening which produces Gamma0) uses a digital elevation model to also correct for the local incidence angle (referring to the topographic surface).
That is correct, but if the backscattering from the ground is directional in any way, Gamma0 cannot correct for that. In that case one is observing different aspects of the target with the different sensors, so the backscatter-difference should be viewed as a signal.