# FY3E GNOS II GNSS Reflectometry: Mission Review and First Results  
[PERSON]  
1 National Satellite Meteorological Center, China Meteorological Administration, Beijing 100081, China; [EMAIL_ADDRESS] (G.Y. ); [EMAIL_ADDRESS] (X.H. ); [EMAIL_ADDRESS] (P.Z. ); [EMAIL_ADDRESS] (N.X. ); [EMAIL_ADDRESS] (X.Z. ); [EMAIL_ADDRESS] (X.X.) 2 Key Laboratory of Space Weather, National Center for Space Weather, China Meteorological Administration, Beijing 100081, China 33 National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China; [EMAIL_ADDRESS] (W.B. ); [EMAIL_ADDRESS] (Y.S. ); [EMAIL_ADDRESS] (J.X. ); [EMAIL_ADDRESS] (F.H. ); [EMAIL_ADDRESS] (C.Y. ); [EMAIL_ADDRESS] (Q.D. ); [EMAIL_ADDRESS] (C.W. ); [EMAIL_ADDRESS] (Y.C. ); [EMAIL_ADDRESS] (M.M. ); [EMAIL_ADDRESS] (G.T. ); [EMAIL_ADDRESS] (P.H. ); [EMAIL_ADDRESS] (C.L.) 4 Beijing Key Laboratory of Space Environment Exploration, Chinese Academy of Sciences, Beijing 100190, China 4  
[PERSON], X.-Y. and abundant GNSS satellites from multiple constellations, which provide stable and continuous transmission signals. After a large number of airborne and land-based experiments, the GNSS-R technique was demonstrated by a series of spaceborne science missions. The first satellite mission was the UK Disaster Monitoring Constellation (UK-DMC) launched in 2003 [7]. It was followed by the UK TechDemoSat-1 launched in 2014 [8]. In 2016, NASA launched the Cyclone Global Navigation Satellite System (CYGNSS), which is a constellation of eight small satellites that can provide ocean surface wind observations with the coverage of latitude \(\pm\)38 degrees for the monitoring of tropical cyclones [9; 10]. In 2019, the first Chinese GNSS-R mission, BuFeng-1 A/B twin satellites, was launched, which retrieved ocean wind speeds using reflected signals from both GPS and BeiDou satellites [11]. In 2020, The ESA FSSCat mission was launched, aiming for land and ice applications. It includes two 6U CubeSats, both of which carry a dual microwave payload combining GNSS-R and an L-band radiometer for interference detection and mitigation [12]. Those science missions provided valuable data for the scientific research, and the potential of spaceborne GNSS-R for the observation of ocean, land and ice has been validated. The FengYun-3E (FY3E) satellite is the fifth of China's FengYun series of polar-orbiting meteorology satellites, following from predecessors FY3C and FY3D. It is the world's first early morning orbit weather satellite that will fill in the gaps of other polar-orbiting meteorology satellites, which are mostly in morning or afternoon orbits. On July 5, 2021, it was successfully launched at the Jiuquan Satellite Launch Center, China [13]. The Global Navigation Satellite System Occultation Sounder II (GNOS II) onboard the FY3E satellite is the upgraded version of the GNOS used on FY3C and FY3D satellites [14; 15; 16]. Besides the GNSS radio occultation (GNSS RO) and precise orbit determination implemented by GNOS, GNOS II can additionally provide GNSS-R measurements. As an integrated GNSS remote sensor, GNOS II can measure the ionosphere, the atmosphere and Earth's surface in three dimensions. One uniqueness of GNOS II is that it can receive GNSS reflected signals from multiple constellations, including GPS, BDS and Galileo. Moreover, GNOS II works together with a scatterometer onboard the same satellite, which provides the potential for cross calibration and validation for both instruments. Another important difference between the FY3E GNOS II and other GNSS-R science missions is that it operates with global data latency of less than 3 hours. Such a short data latency makes the products of GNOS II available for applications such as data assimilation in operational numerical weather prediction (NWP) models and monitoring of tropical cyclones.