Pre-processing Sentinel 1 GRD with SNAP graph


I want to pre-process the Sentinel 1 Data (downloaded with peps) by using SNAP in the context of the detection of irrigated plots and crop monitoring for a Region Of Interest (ROI). The steps of Apply Orbit File, Thermal Noise Removal, Remove GRD Border Noise, Calibration and Terrain correction are mandatory for my study ? And in which step can I add the “Subset” operation in the Graph to study just a region (ROI). Shoud be after Apply Orbit File or after Terrain Correction.

Thank you,

As per the requirement you do subset operation after the step of Apply Orbit file