Methods Study Of GNSS Precise Orbit Determination

With the development of GNSS technology and the flourish of i GMAS,the GNSS orbit determination is becoming the focus of the navigation area and the location based service.This thesis aims to solve three problems during the process of orbit determination: accelerating parameters solution,impact of ERP errors on ultra-predicted orbit orbit and the orbit determination strategy of new-generation Bei Dou-3.The main researches as follow:1.From the principle of precision GNSS orbit determining,the initial orbit determination,the orbit integration,the least square(LSQ)parameter estimation,uncalibrated phase delay(UPD)estimation,ambiguity resolution and SRIF are discussed in detail,which are proved by the corresponding programs.2.With reference to the accuracy and time of rapid and ultra-rapid satellite orbit and the unbalanced distribution of global tracking stations,GNSS Data Analysis Centers are meeting with big challenge.This paper proposes an optimal stations selected model called SSS(Selected Step by Step)which is based on the GDOP(Geometric Dilution of Precision)value of observation equation.Firstly,the calculation methods of optimal and the minimum of ground tracking stations for precise orbit determination were deduced.Secondly,according to the global grid of s~o×s~oand k~o×k~o,the distribution of minimum stations were selected out.Thirdly,based on the standard of minimum GDOP,an optimal distribution of global tracking stations was gradually accumulated step by step.Six days continuous experiment shows,on the same numerical computation ability,SSS model can reach 90% level of accuracy as the whole data processing and reduce computation time at less 50%.Comparing with the ordinary methods,it shows that SSS model can get the same accuracy as the ordinary methods,while could save time reaching up 20%.Moreover,several comparison experiments indicated that SSS is the optimal or sub-optimal model for the station selected and improves the efficient of Data Analysis Centers.3.Due to GNSS Analysis Centers are unable to obtain real-time Earth Rotation Parameters(ERP)accurately,the accuracy of ERP predicted by IERS and IGS are analyzed,and the corresponding orbit 3D RMS is investigated.Impact of ERP errors on GNSS ultra-rapid predicted orbit and a real-time correction method are developed.Based on orbit prediction process,it's found that two main ways dominate the orbit precision.These include:1)orbit integration,and 2)the coordination transformation.The transformation from celestial coordinates system to Earth fixed coordinate system exerts the strongest effect on the accuracy of the ultra-rapid predicted orbit,while the impact of integration can be ignored.To obtain the most accurate ultra-rapid predicted orbit,the correction of predicted ERP is investigated,and a corresponding real-time orbit correction method is developed using the observed part as a reference to adjust the ultra-rapid predicted orbit.To validate the proposed method,three experimental schemes are designed.Experimental results show that the solution for the ultra-rapid predicted orbit accuracy is better using the proposed method than the IERS or IGS products are used.The accuracy of the orbit prediction is enhanced 50% at least,when the correction methods are used.4.Based on the orbit determination tasks of new-generation Bei Dou-3,the orbit estimation strategy is studied in this thesis.First,the data quality of i GMAS will be analyzed from the data preprocessing.Second,two orbit determination strategies are designed.From the results of orbit determination,the “Two Steps”is better than “One Step”,while is a little worse in accuracy.The reason for this phenomenon could be summarized as the accuracy of the reference orbit.