FY3E GNOS II GNSS Reflectometry: Mission Review and First Results

Abstract

FengYun-3E (FY3E), launched on 5 July 2021, is one of China’s polar-orbiting meteorological satellite series. The GNOS II onboard FY3E is an operational GNSS remote sensor that for the first time combines GNSS radio occultation (GNSS RO) and GNSS reflectometry (GNSS-R). It has eight reflection channels that can track eight specular points at the same time, receiving reflected signals from multiple GNSS systems, including GPS, BeiDou and Galileo. The basic GNSS-R output generated by GNOS II is a 122 × 20 non-uniform delay-Doppler map whose high resolution portion captures more information near the specular point. This paper introduces the GNSS-R aspect of the FengYun-3E GNOS II, including the instrument, power calibration and wind speed retrieval algorithm. Preliminary validation results for its first four months of data are also presented. After preliminary quality control, the overall wind speed error is less than 2 m/s at wind speeds below 20 m/s for data from both GPS satellites and BeiDou satellites when compared to the ECMWF reanalysis winds.

Assessment of FY-3E GNOS-II GNSS-R Global Wind Product

“…Observables, the Delay-Doppler Map Average (DDMA) and Leading Edge Slope (LES), are then computed from the DDM BRCS. Details for the L1 processing can be found in [10]. Particularly, the Effective Isotropic Radiated Power (EIRP) of GNSS satellites (GPS and BDS) are estimated by static look-up tables (LUTs) constructed from data collected by two power monitors [10].…”

“…SNR was found to be a good data quality indicator of retrieved winds. The computation of SNR can be found in [10]. Figure 12 shows the histogram and median of SNR for GPS-R and BDS-R.…”

“…The Global Navigation Satellite System Occultation Sounder II (GNOS-II) onboard the FengYun-3E (FY-3E) satellite launched on July 5, 2021, is a GNSS remote sensor that can collect data from both GNSS radio occultation and GNSS-R [10]. The FY-3E satellite is at an altitude of 836 km in a sun-synchronous orbit (SSO) descending in the early-morning at around 6 local solar time (LST) [11].…”

“…Given the sampling frequency of 1 Hz, the spacing of wind samples between one and another on a given track is about 5.6 km. Details of the mission and instrument can also be found in [10]. The first uniqueness of GNOS-II is that it can receive reflected signals from multiple GNSS constellations (GPS and BDS currently, and Galileo soon by sending commands).…”

“…Second, as GNOS-II is at an orbit of high inclination angle, its wind product can achieve nearly global coverage. Finally, since FY-3E is an operational satellite, its data latency is less than 3 hours, which is applicable for operational use and also applies additional requirements to the retrieval algorithm [10].…”