Spaceborne GNSS Reflectometry with Galileo Signals on FY-3E/GNOS-II: Measurements, Calibration and Wind Speed Retrieval

Reflected Global Navigation Satellite System (GNSS) signals from Earth surface can be received by receivers at Low Earth Orbit for the remote sensing of geophysical parameters. While the technique has been studied for around 30 years, most early spaceborne GNSS reflectometry missions only adapted to receive GPS signals and the studies of reflected Galileo (GAL) signals in space are limited. The GNOS-II payload onboard the FY-3E satellite is the first mission that can operationally receive reflected GPS, BeiDou (BDS) and GAL signals at the same time. This paper presents the GAL reflectometry measurements from GNOS-II together with their calibration and wind speed retrieval methods. Results show that while GAL has a different signal modulation, the observables can be used to retrieve wind speeds using the same geophysical model functions of GPS after a dedicated calibration. The retrieved wind speeds from GAL also have a comparable accuracy as those from GPS and BDS.