WV mode processing (SLC to GRD)

Is it possible to process WV mode SLC images to GRD using SNAP?
Then, how can I do that?

When I tried to calibrate one SLC image in WV mode to sigma0, I met an error message like this

Do I need another preprocess before calibration? (I applied band subset before cal)
Or is there any flowchart to make WV SLC to GRD sigma0 dB?