Method And Experiment Of Tropospheric Ducts Inversion Using Ground-Based GNSS Occultation

Tropospheric duct is one important type of atmospheric refraction, which can makeVHF-band radio waves and above form transhorizon propagation. The prerequisite forrational using or avoiding the adverse effects is the effective perceived of thetropospheric duct. In recent years, the problem of remote sensing the tropospheric ductshas been greatly studied. At almost the same time, the technology of remote sensingatmosphere based on signals of GNSS has been widely studied and applied. Thisdissertation proposes and systemically studies the inversion methods for the marinetropospheric ducts from ground-based occultation GNSS signals. The main contents andinnovations are as follows:1. The types, mechanism of formation, and statistical characteristics of thetropospheric ducts are described in detail. The evaporation duct model and troposphericduct model which is needed in the inversion are introduced. The theory and algorithmsto predict radio wave propagation within the tropospheric duct environment arediscussed. The parabolic equation method and ray tracing technology are described andimplemented to analyze the ducting propagation. The path loss predicted by thepropagation model is verified by the experimental data which was obtained over threesea links of various path lengths.2. The key problem of predicting the propagation of ground-based occultationsignals has been mainly studied. To match the circularly polarized GNSS signals, firstly,it is proved that circularly polarized wave can be model by parabolic equation. Secondly,the propagation model of ground-based GNSS occultation signals has been developedby using the combination of ray tracing and parabolic equation. Using reciprocity,another model has been founded to predict occultation signal propagation in thepresence of marine tropospheric ducts. The latter model can be more rationallyimplemented with better utilization of parabolic equation. Simulation and experimentshow the validity of the propagation model in ground-based GPS occultation events.3. A key breakthrough is the development of retrieving tropospheric ducts fromground-based GNSS occultation signals while the GNSS satellites rise or set at the localhorizon over the sea. The model of predicting GNSS occultation signals within thetropospheric duct environment is regarded as the forward model. Then the inversionmethod of retrieving tropospheric ducts has been proposed, and the algorithm has beenrealized, which is based on the forward model and an intelligent optimization algorithm.The range-dependent duct profiles are modeled with K-L expansion, which can be used in the inversion model. According to the inversion model, evaporation duct and surfaceduct are inferred and analyzed with ground-based occultation signals as input.4. The experiment of ground-based GNSS occultation for remote sensingtropospheric was carried out. Statistics and analysis of the occultation events have beenmade. And the influence on the occultation signals has been analyzed, includingreflection or scattering of sea surface, atmospheric refraction and antenna height, etc.Based on large experimental data, the occultation signals are used to retrieve theatmospheric refractivity profiles by artificial neutral networks. In the process ofinversion for tropospheric duct parameters, a convenient approach of retrieving theheight of antenna from the interference signals is proposed. According to the inversionmodel established, the tropospheric duct parameters have been obtained from theoccultation signals received by a ground-based receiver in the end. It is shown that theinversion results are very consistent with the radiosonde observations, which means theeffectiveness of the new technology.5. Evaluation method of tropospheric ducts affecting various types of radars isexplored. Firstly, the relationships of detection probability, coverage region, refractivityprofile and its solving method for conventional radar are presented. Secondly, for thetracking radar, a new algorithm to calculate elevation error based on parabolic equationis presented, which can take the multipath and refractive effects (including ductingeffect) simultaneously. Finally, a method of calculating the ground and sea echoes ofweather radar is presented for the serious issues affecting weather radar data qualitywithin super-refraction or ducting condition. The ground and sea echoes are simulatedand analyzed. The idea of how to apply tropospheric ducts from ground-basedoccultation GNSS signals has been conceived finally.