Radio frequency interference (RFI) is a known issuein low-frequency radar remote sensing. In synthetic aperture radar (SAR) image processing, RFI can cause severe degradation of image quality, distortion of polarimetric signatures, and an increase of the SAR phase noise level. To address this issue, a processing system was developed that is capable of reliably detecting, characterizing, and mitigating RFI signatures in SAR observations. In addition to being the basis for image correction, the robust RFI-detection algorithms developed in this paper are used to retrieve a wealth of RFI-related information that allows for mapping, characterizing, and classifying RFI signatures across large spatial scales. The extracted RFI information is expected to be valuable input for SAR-system design, sensor operations, and the development of effective RFI-mitigation strategies. The concepts of RFI detection, analysis, and mapping are outlined. Large-scale RFI mapping results are shown. In case studies, the benefit of detailed RFI information for customized RFI filtering and sensor operations is exemplified.Index Terms-Calibration, error correction, L-band, radar remote sensing, radio frequency interference (RFI), synthetic aperture radar (SAR).
I. INTRODUCTIONR ADIO frequency interference (RFI) has long been identified as a problem in L-band synthetic aperture radar (SAR), limiting the performance, and applicable signal bandwidth of SAR in many areas around the globe [1]. Most RFI are incoherent electromagnetic interference signals emitted by communication systems, television networks, air-traffic surveillance radars, and other mainly military-based radiation sources whose operating frequency overlaps with the frequency band of a SAR system. RFI usually appear as various kinds of bright linear features in the azimuth-time rangefrequency diagram of a SAR dataset and the interference-to-SAR signal ratio is often high. Incoherent RFI will be partly mitigated by the matched filter process that is applied in the SAR image focusing due to Manuscript
This paper analyzes severe, broadband, radio frequency interference (RFI) signatures that are commonly observed in L-band ALOS PALSAR images acquired close to the North American Arctic coast. These RFI signals are caused by military over-the-horizon radar systems. We introduce the specifics of the interfering signals and demonstrate that standard RFI filters used in the operational ALOS PALSAR processor are insufficient to remove their influence. A new approach for filtering the identified RF interferences is presented and its performance is analyzed by a cross comparison with reference methods. The capabilities of the new correction method are emphasized by presenting several processing results. A statistical and geographical analysis of the strength and distribution of observed RFI signatures is shown, indicating widespread contamination of imagery across the American Arctic coast.
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