Analysis and Mitigation of Radio Frequency Interference in Spaceborne GNSS Ocean Reflectometry Data

With low signal power, Global Navigation Satellite System (GNSS) reflections in space are vulnerable to radio frequency interference (RFI) across the globe which can contaminate observations of GNSS reflectometry (GNSS-R) and introduce bias in the retrieved geophysical parameters. This article presents a comprehensive analysis of the RFI in the Fengyun-3E Navigation Satellite System Occultation Sounder II (FY-3E/GNOS-II) GNSS-R data over the ocean. It was found that major sources of interference are the reflections of regional GNSS and Satellite-Based Augmentation Systems (SBAS), and external L-band interference signals from the ground. Furthermore, interference can have different impacts on the observations through increasing the noise power, decreasing the signal-to-noise ratio (SNR), or biasing observables depending on the type of interference and retrieval method. Some geography-dependent biases in the retrieved wind speeds were found to be related to RFI. An RFI mitigation method is then presented to calibrate observables and reduce geographical wind speed bias for the operational retrieval system. The bias and root-mean-square error of retrieved wind speeds from a region that is affected by RFI were reduced from 1.26 and 2.78 to 0.04 and 1.59 m/s, respectively.