Research On Improvement Of Regional ZTD Model Based On Sounding Data

Tropospheric delay is one of the important reasons that affect the accuracy of GNSS navigation and positioning.At present,the commonly used methods to eliminate tropospheric zenith delay error are parameter estimation method,external correction method and model correction method.Among them,model modification method is favored by experts and users in more and more fields because of its cheapness and universality.Based on the detailed analysis of temporal and spatial variations of tropospheric delay,this paper considers that the global accuracy of Hopfield model and that of Europe and the United States are good,but the accuracy is not good in China.Therefore,based on the Hopfield model,the tropospheric zenith delay adapted to China region is established.Function model,specific study detail and consequence are as follows:(1)The stratification and structure of atmosphere and several meteorological parameters related to tropospheric delay modeling are explained in detail.The variation characteristics of atmospheric refraction dry and wet components with altitude are analyzed.The tropospheric dry delay is calculated directly by Saatamonien model.Its precision can reach millimeter class.Considering the randomness of the wet component,based on the sounding data,the delamination integral method is used to extract the tropospheric wet delay,and the total tropospheric delay can be obtained.(2)based on the meteorological data provided by DORIS station from 2008 to2013,the trends of annual variation of temperature,pressure and water vapor pressure are analyzed qualitatively,and then the correlation between tropospheric delay and temperature,pressure and water vapor pressure is quantitatively analyzed through mathematical statistics.It is found that tropospheric delay is positively correlated with air temperature and water vapor pressure and negatively correlated with pressure.Using VMF1 global grid data to study the relationship between ZTD and station location,it is found that tropospheric delay and height are negatively correlated,that is,when the height of the station is high,tropospheric delay is smaller,and tropospheric delay is with the tropospheric delay.The tropospheric delay tends to decrease with the increase of latitude,the maximum tropospheric delay occurs near the equator and the minimum occurs near the poles,while the tropospheric delay haslittle correlation with longitude.(3)the time and Fourier variation of tropospheric zenith delay are analyzed.It is found that ZTD has obvious annual and semi-annual periodicity,showing the characteristics of large tropospheric delay in summer and small in winter.Therefore,based on the Hopfield model,the annual and semi-annual periodic terms are added,and the GHop model suitable for China is established.The accuracy of the new model is evaluated by using the tropospheric delay extracted from the sounding data as the true value.By comparing with two classical tropospheric delay models with meteorological parameters,Hopfield and Saastamoinen models,it is found that GHop The model is better than the two classical models.In this paper,the radiosonde data from 45 sounding stations in China are analyzed.The results show that the average accuracy of Hopfield model,Saastamoinen model and GHop model are ±48.68 mm,respectively.The ±46.84 mm and ±36.8mmGHop models have an average increase of 24.4mm compared with the Hopfield model,and 21.4mm relative to the Saastamoinen model.The new model can better express the nonlinear variation process of tropospheric delay.Certain application value.