Radio Occultation Technology Research Based On Ray-tracking Algorithm

As the new atmospheric detection technique,radio occultation has a wide range of applications in astronomy,geography and national defense for its high resolution and long-term stability.This study has realized the forward simulation program based on radio occultation technology and ray-tracking algorithm,which can calculate temperature,pressure,electron density and refractive index through the atmospheric and ionospheric model.After that,the ray path between GPS and LEO(Low Earth Orbit)can be simulated,and phase delay can be calculated.The efficiency of occultation data processing is greatly improved by this program.Firstly,the theoretical framework and principle of ray-tracking algorithm has been elaborated.This forward simulation program contains 3 modules,which is ray path preprocessing,error correction and LEO tracking.The function of each module and the relationship between then are analysed.Ray path can be calculated step by step through these modules,so that the phase delay of GPS signal caused by atmosphere can be further acquired.The feasibility of ray-tracking forward simulation program is verified using space-based and mountain-based occultation data.For the space-based occultation,satellite coordinates and phase delay measured data are provided by the COSMIC website.The ionospheric electron density and atmospheric temperature are obtained using the known earth atmosphere models,and then the radio wave propagation path is calculated according to the refractive index at each point.The measured phase delay is in good accordance with the simulation value.The results show that the ray-tracking forward simulation program can be used for space-based occultation data processing.For the mountain-base occultation,a mountain-base occultation experiment was carried out on the Jiugongshan Mount in 2015.The satellite coordinates were provided by the IGS Precision Ephemeris and the carrier phase values were collected by the hardware receiver.As the sampling frequency of the hardware receiver is not consistent with the output frequency of satellite coordinate,the Chebyshev interpolation method is used to interpolate the satellite coordinates.Compared the carrier phase simulation values with the measured values,the experimental results show that the ray tracing algorithm can be used for mountain-base occultation data processing.In this paper,the feasibility of the ray-tracing forward simulation program is verified by the space-based and mountain-based occultation data.It is proved that the algorithm can be applied to occultation data processing.The stability and real-time performance of the program is well,the operation efficiency is high,which provides the research foundation for the occultation inversion technology,and has certain guiding significance in the ray path calculation and the mountain-based occultation.