Research On Ambiguity Resolution For Precise Point Positioning And Regional Modeling Of Atmospheric Delay

Precise point positioning(PPP)integrates the flexibility of traditional single point positioning and the high precision of network RTK,which only uses a single receiver to achieve high precision positioning in centimeter level.It is not only one of the key technologies to realize the global real-time precise dynamic positioning and navigation,but also the most advanced hotspots in the field of GNSS.At present,most of the PPP services are based on float solution.The PPP float solution limits the application of PPP,which leads to the positioning accuracy and stability that is not as good as network RTK.Therefore,it is of great significance to study the theories and methods of ambiguity fixing,thus can promote the wide applications of PPP technique in engineering and other fields.Atmospheric delay is one of the main factors that limit the convergence time and positioning efficiency of PPP,so how to establish an accurate correction model of atmospheric delay is of great significance to the realization of fast and efficient PPP.In this paper,the basic theory and method of PPP are studied systematically.The essential reason for the loss of integer characteristics of the float ambiguity is analyzed.Based on the ambiguity-fixed algorithm of Integer Recovery Clock(IRC),the fixed-solution of PPP ambiguity is realized.Based on the deep analysis of the spatio-temporal characteristics of tropospheric delay and ionospheric delay,the regional modeling methods of tropospheric delay considering the difference of elevation and horizontal position as well as of ionospheric slanting delay based on the Ionospheric Pierce Point(IPP)are proposed,which can be used as atmospheric constraints for the regional augmented PPP.The main contents and work of this paper are as follows(1)The basic theory and methods of PPP are introduced in detail,including mathematical model,error correction,data preprocessing and parameter estimation.The receiver and satellite bias are systematically studied,and the essential reason that the traditional PPP ambiguity can not be fixed is analyzed.Based on the ambiguity-fixed algorithm of IRC,the PPP ambiguity is fixed step by step with the method of partial ambiguity resolution(PAR)considering quality control.Numerous experimental results show that the convergence speed of PPP can be greatly accelerated by multi-GNSS combinated,the convergence time of NEU direction is shortened by about 15.1%;the ambiguity-fixed solution can obviously improve the positioning accuracy,the RMS values of the NEU direction are reduced by 45.4%,31.6%,20.1%,respectively.(2)The spatio-temporal characteristics of tropospheric delay are analyzed.Considering the relationship between troposphere delay and elevation and horizontal position,a regional modeling method,which considers the difference of elevation and horizontal position,is proposed.Tropospheric delay is separated into the elevation and horizontal components,which are regional modeled,respectively.The priori tropospheric delay of rover station is interpolated to enhance the PPP with consideration of tropospheric delay constraints.Results show that:the accuracy of the tropospheric delay obtained from the PPP with fixed station coordinates is within 8mm;the elevation and horizontal components after be separated are closely related to the elevation and the horizontal position,respectively;the PPP with consideration of tropospheric delay constraints can significantly improve the positioning accuracy of North and Up directions,the RMS values are reduced by 10.0%,23.2%,respectively.(3)The spatio-temporal variation and characteristics of ionospheric delay are analyzed.Considering the surface characteristics of the ionosphere single layer,the ionospheric delay is naturalized to the IPP A modeling method of the ionosphere slant delay based on the location of the IPP is proposed,and the priori constraints of the ionosphere delay are interpolated through the IPP at the rover station to enhanced PPP.Experimental results show that the ionospheric delay derived from the PPP with fixed station coordinates is in accordance with the GIM results;the difference between the interpolated value of the ionospheric delay and the estimated value from the rover station is within 2TECU;with consideration of ionospheric delay constraint,the PPP converging to within 10cm becomes more faster.The time is reduced from about 22 minutes to 17.5 minutes.