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Inversion Methods for Ionospheric Occultation from GPS Observation Data

2004; Wiley; Volume: 47; Issue: 4 Linguagem: Inglês

10.1002/cjg2.3534

2326-0440

Zhen Zeng, Xiong Hu, Xunjie Zhang, Wei‐Xing Wan,

Geophysics and Gravity Measurements

Abstract Based on the assumption of the local spherical symmetric ionosphere, we derive two inversion methods with which ionospheric density profiles are extracted from the dual frequencies and single frequency radio occultation data. The estimation errors of the dual‐frequencies method come from errors of the carrier phase measurements, while the errors of the single frequency method are mainly determined by the precision of the pseudo‐range measurements. Since the pseudo‐range measurements tend to be about 100 times noisier than those of the carrier phase, the retrieval precision with the dual‐frequencies method may be generally higher than that with the single frequency. However, slightly different paths of carrier L 1 and L 2 will bring errors to estimations of the dual‐frequencies method. The radio occultation simulation results with a three‐dimensional ray‐tracing program are used to evaluate these inversion methods. Results show that the inversion profiles agree very well with the given model ionosphere, which suggests reliabilities and accuracies of both methods. Then, two inversion methods are applied to the processing of GPS/MET data for ionospheric occultation. The inversion results indicate reasonable ionospheric profiles. Inversion profiles by the single‐frequency method are consistent with those by the dual‐frequencies method. It provides the theoretical inversion base for ionosphere radio occultation observations with a single frequency GPS receiver onboard LEO.