Using 1 second LEO clock corrections for the Fengyun-3E radio occultation retrievals

Abstract. Clock offset constitutes a major error source for Global Navigation Satellite System (GNSS) radio occultation (RO) products, particularly for stratospheric observations. The adoption of high-rate clock correction strategy can effectively mitigate clock offset induced errors. In this study, high-rate (1-s) undifferenced (UD) Low Earth Orbit (LEO) clock corrections are used to retrieve RO observations from the Fengyun-3E (FY-3E) satellite. The retrieval results are compared with those derived from the conventional 30-s clock correction scheme and the single-difference (SD) scheme currently adopted in the official data processing. The results demonstrate that the 1-s LEO clock correction scheme improves the overall quality of FY-3E RO retrievals. For bending angle, the most prominent improvements are found in the altitude range of 40-60 km. Globally, its systematic difference is roughly 3% smaller than that of the 30-s scheme and 1% smaller than the SD scheme. Such superiority further propagates downward to refractivity and dry temperature. For refractivity, the largest improvements are also found in the altitude range of 40-60 km with systematic differences for the 1-s UD scheme reduced by approximately 0.5% relative to the other two schemes. Standard deviations of the 1-s scheme remain consistently smaller across the complete height range. Standard deviations of dry temperature are also improved with standard deviations about 0.5% smaller than SD and 1% to 2% smaller than the 30-s scheme in the altitude range from 0-40 km. The results in this study demonstrate the capability of using 1-s clock correction scheme for further promoting Fengyun GNSS Occultation Sounder-II (GNOS-II) RO observations. The results here can provide support for future operational processing and archive reprocessing of all Fengyun GNSS occultation datasets.