Profiling Tropospheric Refractivity Based On Single Ground-based GPS Receiver

The tropospheric refractivity profile is the basis for radio wave correction for refractive error, however, there is not a simple and convenient method to measure it for all-weather in real time at present. The Global Navigation Satellite System(GNSS) have been applied successfully not only in the traditional field such as ranging, time service, and navigation, but also in environmental monitoring, geodesy, astronomy, and meteorology and so on. On the basis of estimating electromagnetic wave refraction parameters (path delay and bending angle) by single ground-based GNSS receiver, the retrieving algorithms of tropospheric refractivity profile have been investigated herein. The main topics and results of the study are as follows:Firstly, the general methods of obtaining tropspheric delay by the Precise Point Position method (PPP) depend upon the precise IGS (the International GPS Service) final products, which are usually available on the thirteenth day after the last observation, therefore the tropospheric delays can not be acquired in real time. On the basis of the PPP method with IGS ultra-rapid products, new techniques are developed here of calclulating the benging angle and the slant path delay (STD) at the straight line elevation below 5°in real time. The experiment show that the RMS errors of the estimated STDs by the methods are less than 5%.Secondly, on the assumption that the tropospheric refractivity profile approximates to some model, the retrieving methods are proposed for estimating the parameters of the model by some searching algorithm by path delay of GNSS receiver. The main advantage of this method is that the historical radiosonde data are not necessary here.Thirdly, the statistical relationships between simulated path delay and atmospheric refractivity at various height based on historical radiosonde data have been analysed, and it is found that there are good correlations between them. Therefore the regressing models are founded between (a) surface meteorologic parameters and simulated tropospheric path delay and (b) tropospheric refractivity profile.Fourthly, the BP (Back Propagation) neutral network, SVM (Support Vector Machine), LS-SVM (Least-Squre SVM), and RVM (Relevance Vector Machine) are used to model tropospheric refactivity profile by the STDs, and these models are compared by simulation and experiment. The RVM model based on the differences of the STDs at various straight line elevations has the best performance, especially for tolerating the errors of the retrieved STDs.Fifthly, combining (a) the estimation method of the slant path tropospheric delay (STD) at low straight line elevation (<5°) of single ground-based GNSS receiver in real time and (b) the RVM inversion method based on the differences of STDs, a method is developed for retrieving atmospheric refractivity profiles in real time based on single ground-based GPS receiver, which solves the difficulty of inversion in real time. The simulation and experiment indicate the validity of the method.The studies in this dissertation propose a new method to retrieve atmospheric refractive profile in real time, at low cost, and high efficiency. The results herein will be helpful for correction for tropospheric refractive error of radio wave in electronic systems including TT&C (Telemetry, tracking, and commanding), navigation, radar, etc.