Research On Precise Point Positioning Technology Based On BDS In Polar Regions

President Xi and Central Committee of the Communist Party of China put forward an important strategic thinking on the construction of the strong marine power.One of the major decisions is to expand our polar strategic interests.On the Chinese polar affairs,we carried out our polar expedition depending on GPS in the long term,which is lack of autonomy.Coverage of BDS,well improved and developed recently,is gradually enlarged around the world.It is imperative to use the BDS for polar scientific research and satellite navigation applications for providing stable,reliable and high-precision navigation and positioning services.Compared with the relative positioning mode,PPP can be achieved in Polar Regions to determine the high-precision location.It Also can be efficient and helpful to save manpower and resources.However,current researches and applications in polar mainly focus on GPS.There are few researches on polar PPP in BDS,especially the practical application of BDS PPP in the polar regions.This paper aims to analyze characteristics of polar BDS PPP,including a small residual value,a low satellite elevation and the special climate.Then we propose corresponding methods to improve the PPP performance of BDS in polar based on these characteristics.The main work and contribution of this paper are as follows:1.For the unevenness coverage of BDS visible satellite number and PDOP value in polar regions,the BDS observations in polar regions are divided into three categories according to observation conditions,Then PPP performances of the three type of regions are analyzed and the priori weight matrix is found inappropriate.2.The residual characteristics of the carrier phase and pseudo-range of BDS PPP are analyzed statistically for the accuracy presentation.It is found that observations residuals of BDS PPP carrier phase in polar are generally smaller than those of the stations at middle and low latitude.According to the residual characteristics of BDS PPP,a method to preseting the weight for BDS Classified-Satellite observations based on variance-covariance component estimation of Helmert in polar region is proposed.This model is established based on the measured data and proved to have improved the BDS PPP performance.3.In view of the fact that the satellite elevation angle in the polar region is generally low,the elevation elega cutoff angle which is more suitable for the polar BDS PPP has been proposed after the comparison of the observation condition,the zenith tropospheric delay estimation and positioning accuracy.4.The GPT2-Saas zenith tropospheric delay correcting model is firstly proposed to be used in Polar Regions which is the combination of the Saastamonien model,GMF mapping function and GPT2 high-precision meteorological model,replacement of the measured meteorological data which is difficult to obtain.The GPT2-Saas model has better performance in accuracy of the zenith tropospheric delay estimation and positioning than UNB3 model and EGNOS model.5.For the limit of the single BDS PPP performance in whole polar regions under all processing modes,the multi-GNSS combined PPP based on BDS is applied to Polar Regions to improve the performance of positioning accuracy and reliability.Compared with the single BDS PPP,the multi-GNSS combined PPP has a greater improvement in the performance of the convergence time,positioning accuracy and reliability solutions,especially in the dynamic mode.