Research On Tropospheric Delay Model In The Northern Hemisphere

Tropospheric delay is one of the main factors affecting the precision of satellite navigation and positioning.There are four methods to eliminate the the tropospheric delay error in current,which main include external correction,parameter estimation,model correction and difference method.At present,the method of model correction is the most widely used.This paper analyses the effect of spatiotemporal variation on the troposphere delay,and then establishes the tropospheric delay function model based on the Hopfield model.This paper does some study specifically in the following research areas:(1)The tropospheric delay in the northern hemisphere is extracted using meteorological data from the global upper air sounding station provided by the University of Wyoming web site.The atmospheric refractive index of the northern hemisphere is analyzed in detail.It is found that the refraction index shows a significant negative exponential relationship with the height change.Therefore,the atmospheric refractive index is fitted by the piecewise negative exponential function to obtain the tropospheric delay.(2)The tropospheric delay of the sounding station is calculated by interpolating based on the VMF1 global grid tropospheric delay,which is compared with the extracted tropospheri delay to analyse the reliability.It is found that the accuracy of extracted tropospheric delay is about 4 mm,and the empirical models can reach 3-7cm.So,the extracted tropospheric delay can be regarded as an approximate true value,which can be used to establish tropospheric delay region model latter.(3)Study on HL tropospheric model with latitude parameters.The difference of tropospheric delay in different spaces of the northern hemisphere was analyzed,it is found that latitude has a significant effect on the troposphere delay,but different longitude has little effect on it at the same latitude.At the same time,the seasonal variation of the tropospheric delay is studied.We can know that the troposphere delay has obvious periodic or semi-periodic characteristics with time.On the basis of it,a new modified model HL model taking latitude parameters into account based on Hopfield model is proposed,and the concrete expression of HL model is given.(4)The tropospheric delay extracted from sounding data is used as the true value to analyze the HL model accuracy.The HL model is greatly improved comparing with the Hopfield model and Saastamoinen model.The average precision of the Hopfield model,Saastamoinen model and HL model are ± 31.85mm,± 34.37mm and ± 25.58mm respectively.The HL model increases 19.7%compared with the Hopfield model,and it increase 27.5%in November.Compared with the Saastamoinen model,the HL model increase 25.6%,in March increased 30.1%.