Radio Frequency Interference (RFI) is a known issue of low-frequency Synthetic Aperture Radar (SAR) data. In this paper, a processing system is described that is successful in detecting, characterizing, and mitigating RFI signatures in data of the L-band SAR system ALOS PALSAR. An RFI analysis system that is integrated into the SAR processor is logging a wealth of RFI-related information that is used to map, characterize, and classify RFI signatures across large spatial scales. The concept of the RFI detection and mitigation algorithm is described, the RFI analysis concept is outlined, and examples of spatial RFI maps are shown.