A Decade of GNSS Signal Disruptions in SMAP-R Full-Polarimetric Observations Worldwide

Global Navigation Satellite System Reflectometry(GNSS-R) signals are frequently used to analyze surface scatteringproperties at L-band, providing valuable observations of Earth’ssurface conditions. However, GNSS-based remote sensing isinherently vulnerable to radio-frequency interference (RFI) andsignal disruptions, particularly in conflict zones where electronicwarfare tactics may be employed. According to a study of theStrategic Studies Institute (SSI) US Army War College, theUkraine-Russia war, for example, has seen an unprecedented levelof GNSS denial operations, with military and tactical jammingsystems deployed to disrupt satellite-based navigation andcommunication. Such interference not only affects positioning,navigation, and timing (PNT) services but also has significantimplications for remote sensing systems that rely on GNSS signals.This study examines worldwide detections of RFI through L2cGNSS-R measurements through the Soil Moisture Active PassiveReflectometer (SMAP-R) in the last decade. While the RFI wouldbe detected by any GNSS-R mission with worldwide coverage,employing SMAP-R data enables worldwide observations of theRFI dating back to 2015, and enables measuring the polarimetricimprint of the RFI over time for the first time. RFI is extensivelydetected over East Europe, arising from regions affected by theUkraine-Russia war. Additionally, the conflict in Syria, and thecivil war in Burma are both very distinctive areas. Besidesobserving an increased noise in the GPS L2c band, whichtranslates into a dramatically reduced signal-to-noise ratio (SNR),SMAP-R shows anomalous polarimetric responses resulting fromthe signal distortion, the degraded signal coherence, and theunexpected scattering patterns of interfering signals transmittedfrom jammers. SMAP-R proves a vast depolarization of the GNSSsignal through the Stokes and child Stokes parameters. RFI overthose areas makes the retrieval of geophysical parametersunfeasible. A flagging methodology is defined as it is being addedto the SMAP-R dataset.