Processing RADARSAT-2, TerraSAR-X, and ALOS 2 data

yes, for all mentioned sensors, radiometric calibration (Menu > Radar > Radiometric > Calibration) will derive Sigma0 as the backscatter coefficient.
The only thing required is that you import yourd data correctly (Menu > File > Import > SAR > …) so that SNAP is able to recognize the sensor behind the data and apply the calibration accordingly.

Please also see here: What is sigma0

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