Accuracy Assessment of the Doppler Frequency and Pseudorange Model Based on GPS/LEO Radio Occultation
The Doppler frequency and pseudorange model are important information for open-loop tracking of GPS/LEO signal. The Doppler frequency model can be predicted through iteration, with the use of a bending angle/refractivity climatology and satellite orbits. The pseudorange model can be obtained by multi-epoch or single-epoch algorithm. About 7279 COSMIC radio occultation soundings, from DOY (day of year) 71 to DOY 73 in 2007, recorded in open-loop mode are processed by above-mentioned algorithms, the calculated Doppler frequency and pseudorange model are compared with corresponding COSMIC observations. The statistical comparisons of the difference between COSMIC Doppler frequency observation and Doppler frequency model show: above 2 km impact height, the mean Doppler frequency shift caused by the Earth’s neutral atmospheric condition is less than 3 Hz, the corresponding standard deviation is less than 6 Hz. The mean and standard deviation of the difference between COSMIC phase observation and pseudorange model calculated by multi-epoch algorithm are less than 15 m and 23 m, respectively, above 2 km. Similar results can be found in the single-epoch algorithm. The accuracy of the pseudorange model calculated by single-epoch algorithm is better than that of multi-epoch algorithm. Therefore, the atmospheric Doppler and pseudorange model predicted by the single-epoch algorithm can be used to track the GPS radio occultation signals recorded in the open-loop mode.
KeywordsGPS/LEO occultation Open-loop Closed-loop The doppler frequency Pseudorange
The authors are grateful to University Corporation for Atmospheric Research (UCAR) for access to COSMIC RO data and ECMWF analysis data. This research is supported by the National Natural Science Foundation of China (11273047, 41305016), the Natural Science Foundation of Zhejiang province (LQ13D050002) and the Natural Science Foundation of Ningbo (2014A610156).
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