Range-Frequency Domain Iterative Notch Filtering Method for RFI Mitigation in SAR

As the electromagnetic environment increases complexity, electromagnetic signals in the same frequency band will interfere with a synthetic aperture radar (SAR), causing distortion in SAR images. Most notch filters set a fixed threshold and zero notch to achieve radio frequency interference (RFI) suppression, which is not adaptive when the energy level of the RFI varies. In this letter, an iterative notch filtering method based on range-frequency domain outlier detection is proposed. It uses hybrid indicators to distinguish the differences of the range spectrum of the Z-normalized SAR single-look complex (SLC) image and the zero-mean complex Gaussian distribution and obtains an adaptive detection threshold based on spectrum data to detect anomalies. Then, 2-D notch filters are constructed to achieve RFI mitigation. In addition, the proposed method performs the above operations with adaptive thresholds in an iterative manner by setting termination conditions to suppress remaining RFI. Compared with other methods, the proposed method can offer more precise RFI detection and effective RFI mitigation. Experiments based on simulated and real SAR data demonstrate the efficacy of the proposed method.