Research On Methodology Of GNSS Single Frequency PPP For Atmospheric Delay Correction

Single-frequency receivers have been widely used in the satellite navigation and positioning fields due to their advantages such as low cost,low power consumption and small storage space required.However,the single-frequency receiver has defects,such as long convergence time and low positioning accuracy.Based on this,this paper studies the GNSS single frequency precise point positioning(PPP)constrained by atmospheric delay.Mainly include cycle slip detection and repair of single-frequency,tropospheric and ionospheric delay models,atmospheric delay-constrained single-frequency PPP,etc.The main research contents and results are as follows:(1)This paper briefly summarizes the PPP mathematical model,parameter estimation methods and main error correction processing,and then the accuracy of the CSRS-PPP online solution results are evaluated.After analyzing the online data processing results of 10 MGEX stations evenly distributed in the world for three years in different seasons,it is concluded: taking the SNX released coordinates as the reference true value,the residuals and RMS values in the three directions of E,N and U and the average RMS value during the experiment period are all within 1cm.Therefore,if there is no reference truth value in the SNX file,the CSRS-PPP online solution result can be used as the reference truth value.(2)Aiming at the shortcomings of traditional single-frequency cycle slip detection and repair methods,which are sensitive to sampling interval and ionospheric delay,and have low success rate of cycle slip repair,therefore,based on the Satellite-specific Epoch-differenced Ionospheric Delay(SEID)model,this paper proposes a cycle slip detection and repair method suitable for single-frequency observations.The experimental results show that the model can effectively detect different types of cycle slip combinations(including small cycle slip,equal cycle slip and special cycle slip),and the cycle slip repair value is correct.(3)The influence of nine tropospheric delay mapping function models(MFM1?9)on tropospheric delay and positioning accuracy under five single-frequency combined systems is systematically analyzed.Five single-frequency combination systems include single GPS(single G),single GLONASS(single R),dual system combination(GPS+GLONASS,GR),three system combination(GPS+GLONASS+BDS,GRC)and four system combination(GPS+GLONASS+BDS+GALILEO,GRCE).The experimental shows: compared with the single system,the repetitiveness percentage of the combined system has increased.Except for the MFM1 and MFM3,the repeatability percentages of the other seven mapping function models improved exceeded 70%;single G positioning results have the highest increase in repeatability percentage in the E direction,single R and GR positioning results have the highest increase in repeatability percentage in the N direction,and GRC and GRCE positioning results have the highest increase in repeatability percentage in the U direction;different mapping function models have little effect on the E,N and U direction results of five single frequency combination systems.(4)Systematically analyze the influence of seven meteorological parameter models(MP1 ? 7)on tropospheric delay and positioning accuracy under five single-frequency combined systems.It's concluded that: different meteorological parameters calculation method has little effect on the accuracy of tropospheric delay and positioning results.The calculation method of different meteorological parameters added to the horizontal gradient model correction has been improved by more than57.7%.The positioning results of single G added to the horizontal gradient model correction are improved the most in the E direction,single R and GR are the most improved in the N direction,and GRC and GRCE are the most improved in the U direction.Adding the correction of the horizontal gradient model to the tropospheric delay increased by more than 60%,and the MFM1 and MFM3 models have a lower improvement than the other seven projection function models.Compared with the standard atmospheric parameters,the positioning results of each combined system to the statistical results of the calculation method of different meteorological parameters with the correction of the horizontal gradient model are similar.(5)Based on the SEID model,a single-frequency observation value is proposed to invert the dual-frequency observation value,and then combined with the spherical harmonic function model,the phase smoothing pseudo-range method is used to calculate the satellite and receiver DCB and ionospheric delay.It is concluded that the DCB of satellites calculated by this method are mostly within ±0.5ns compared with the reference true values,the ionospheric delay is within ±20tecu,which is slightly larger than the results of the existing literature.After analysis,it is believed that the main reason is that the spherical harmonic function model ignores the internal characteristics of the ionosphere,and the lack of IGS and MGEX stations around the station,which results in the low precision of GIM products.(6)The influence of the four interpolation methods of GIM products NENE,BILI,BICU and JUNK on the convergence time,positioning accuracy and calculation time is analyzed.It is concluded that the BILI interpolation method is the best.In static and simulated kinematic modes,the TIC3 constraint method has the largest convergence improvement in the horizontal and vertical directions.The TIC1 constraint method improves the convergence in the vertical direction more,and the TIC2 constraint method improves the convergence in the horizontal direction.The accuracy of the final positioning results of the four constraint methods is roughly the same.Increasing the tropospheric delay constraint in the MS period can shorten the convergence time and improve the positioning accuracy;in the low latitude band,the RMS value of TIC3 and TIC2 are almost the same,and the RMS value of TIC2 in the MS period compared with in the NMS period is up to 7.9 cm;in the mid-latitude band,TIC2 has the shortest horizontal convergence time in the NMS period;the convergence time of TIC2 in the NMS period is at least 5.6% shorter than that in the MS period;in the high-latitude band,the RMS value of TIC3 during MS is smaller than that of TIC2,and the RMS value of TIC2 during MS is larger than that of NMS.(7)Systematic evaluation of CLK93 product quality and real-time single frequency PPP accuracy.It is concluded that the availability of GPS and GALILEO system satellites is the highest,GLONASS is the second,and the BDS system has the worst availability.The main reason is that the instability of the data stream network.The RMS value of the real-time orbit products of GPS and GALILEO system in the three directions of radial,tangential and normal are basically less than 5cm,most of the GLONASS system is less than 8cm,and the BDS system only has the radial error RMS value of about 5cm.The RMS value of tangential and normal error exceeds10 cm.The equivalent distance values of the RMS mean values of GPS and GALILEO clock errors are 0.020 m and 0.021 m,respectively,while BDS and GLONASS can reach 0.079 m and 0.059 m.In the real-time static and simulated kinematic modes of single G and GR system,TIC3 has the fast convergence time in the horizontal and vertical directions.TIC1 improves the convergence speed in the vertical direction,and TIC2 improves the convergence speed in the horizontal direction.