Preliminary validation of the refractivity from the new radio occultation sounder GNOS/FY-3C

Mi Liao,Wei-Hua Bai,Yue-Qiang Sun,Peng Zhang,Xiang-Guang Meng,Yan-Meng Bi,Yan Liu,Guang-Lin Yang,Qi-Fei Du

doi:10.5194/amt-9-781-2016

Abstract

Abstract. As a new member of the space-based radio occultation sounders, the GNOS (Global Navigation Satellite System Occultation Sounder) mounted on Fengyun-3C (FY-3C) has been carrying out atmospheric sounding since 23 September 2013. GNOS takes approximately 800 daily measurements using GPS (Global Positioning System) and Chinese BDS (BeiDou navigation satellite) signals. In this work, the atmospheric refractivity profiles from GNOS were compared with the ones obtained from the co-located ECMWF (European Centre for Medium-Range Weather Forecasts) reanalysis. The mean bias of the refractivity obtained through GNOS GPS (BDS) was found to be approximately −0.09 % (−0.04 %) from the near surface to up to 46 km. While the average standard deviation was approximately 1.81 % (1.26 %), it was as low as 0.75 % (0.53 %) in the range of 5–25 km, where best sounding results are usually achieved. Further, COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) and MetOp/ GRAS (GNSS Receiver for Atmospheric Sounding) radio occultation data were compared with the ECMWF reanalysis; the results thus obtained could be used as reference data for GNOS. Our results showed that GNOS/FY-3C meets the design requirements in terms of accuracy and precision of the sounder. It possesses a sounding capability similar to COSMIC and MetOp/GRAS in the vertical range of 0–30 km, though it needs further improvement above 30 km. Overall, it provides a new data source for the global numerical weather prediction (NWP) community.

Highlights

When a ray transmitted by the Global Navigation Satellite System (GNSS) passes through the atmosphere, the signal received by the GNSS receiver on a low Earth orbit (LEO) satellite is bent and delayed
In addition to different latitudes, we evaluated the deviation of GNOS GPS from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis in winter and summer
The results show that the mean bias and standard deviation of refractivity between GNOS GPS (BDS) and ECMWF reanalysis are about −0.09 (−0.04) and 1.81 % (1.26 %), respectively, from the near surface to the altitude of 46 km

Summary

Introduction

When a ray transmitted by the Global Navigation Satellite System (GNSS) passes through the atmosphere, the signal received by the GNSS receiver on a low Earth orbit (LEO) satellite is bent and delayed. With the advantages of high vertical resolution, high accuracy, all-weather sounding, self-calibration, long-term stability, global coverage, and low cost, RO-based operations were regularly carried out, some of which include the German CHAMP (CHAllenging Minisatellite Payload; Wickert et al, 2001), the Argentinian SAC-C (Satellite de Aplicaciones Cientificas-C; Hajj et al, 2004), the US/German GRACE (Gravity Recovery and Climate Experiment) (Beyerle et al, 2005), the Taiwanese/US COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate; Anthes et al, 2008), and the European MetOp/GRAS (GNSS Receiver for Atmospheric Sounding) mission (Von Engeln et al, 2009). The first satellite-based RO instrument named GNOS (Global Navigation Satellite System Occultation Sounder) was launched on 23 September 2013 and mounted on the Chinese polar orbiting meteorological satellite Fengyun-3C (FY-3C) (Bai et al, 2014)

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Conclusion