The EAR Radio Frequency Interference Detection and Geolocation Methodology: Application to the NASA-ISRO Synthetic Aperture Radar (NISAR) Geocoded Polarimetric Covariance Product

Abstract

The National Aeronautics and Space Administration (NASA) Indian Space Research Organization (ISRO) synthetic aperture radar (SAR) (NISAR) mission February 2026 public data release includes 13 803 Level-2 Geocoded Polarimetric Covariance (GCOV) granules reporting measured normalized radar cross sections (NRCSs). An investigation of L-band radio frequency interference (RFI) in the GCOV product is presented that demonstrates the susceptibility of the mission’s observations to anthropogenic transmissions. An “Elliptical ARtifact” (EAR) RFI detection and geolocation methodology is described and applied to NISAR GCOV products. Because GCOVs represent multilooked measurements, existing RFI detection methods that process “raw” in-phase and quadrature backscatter returns are not applicable. The EAR method instead performs detections based on the “shape” of backscatter intensity anomalies consistent with the properties of NISAR’s SweepSAR mode of operation. Results in the vicinity of known sources of interference are used to demonstrate the performance of the EAR method. Larger scale tests further reveal 2396 detections representing more than 500 distinct sources across locations included in the February 2026 public data release. The majority of the sources identified in this “proof of concept” demonstration do not appear to have been previously reported, so the need for RFI detection beyond that available from a priori information on potential RFI sources is emphasized. The use of NISAR’s multiple operational modes in characterizing RFI source properties is also demonstrated. While future NISAR data releases are expected to include additional mission-provided RFI detection and mitigation, the EAR technique will remain useful for independent assessment of mitigation performance and for identifying residual RFI corruption in the NRCS products of NISAR or other SAR missions.