In-orbit performance of GNOS on-board FY3-C and the enhancements for FY3-D satellite

The Global Navigation Satellite system Occultation Sounder (GNOS) instrument on each of the Fengyun 3 (FY3) series meteorology satellites is a global navigation satellite system radio occultation (RO) payload used for remote sensing of the earth's neutral atmosphere and ionosphere. The GNOS, the world's first RO sounder compatible with both the BeiDou (BD) navigation satellite System (BDS) and the Global Positioning System (GPS), can observe around 700 (500 GPS + 200 BDS) RO events per day. This payload can receive BDS/GPS dual-frequency signals using the B1/B2 closed-loop (CL), GPS L2 semi-codeless, GPS L2C CL, GPS L1 C/A CL, and GPS L1 C/A open-loop (OL) tracking methods. This paper assesses the in-orbit performance of the Fengyun 3-C satellite (FY3-C) GNOS instrument, including the warm start time, the number of satellites tracked for positioning, carrier phase measurement errors, open-loop tracking performance, real-time navigation error analysis, the number and distribution of occultation events and Precise Orbit Determination (POD) error statistics, and illustrates the performances' results which shows the stability and feasibility of FY3-C GNOS. Moreover, the enhancements to be implemented on the Fengyun 3 D (FY3-D) satellite for a planned September 2017 launch include extended occultation channel numbers, open-loop tracking for both L2C and B1I carrier phases, and optimized antenna patterns.