Research On Key Technologies And Applications Of The New-generation Geodetic VLBI

This dissertation focuses on several key technologies and applications of the new-generation geodetic VLBI system(namely VGOS),which could be helpful for VGOS construction and operation in the future.Main work and achievements can be concluded as follows.1.The proposal and system composition of new-generation VLBI observing system were summarized,as well as the status quo and trend at home and abroad.Also,some issues of researchable value were proposed.Then basic methodologies related to VLBI were studied,including the principle of radio interferometry and geometric time delay of VLBI in near and distanced fields,all kinds of corrections in observation model,generation of schedules and virtual observables in simulation experiments,and also two widely used data processing methods.2.The influences of different global distributions of VGOS stations and various network scales on the accuracy of station positions and EOPs were analyzed.In terms of different kinds of hardware specifications,which includes antenna diameter and slew rate,site clock error,system SNR,time delay measurement noise,record band and qualification bit,quantitative analysis of effects on observation results was conducted.3.A global and whole-year hydrostatic delay correction model was constructed,which could be exploited to calculate system offset of hydrostatic delay models at any place and any time on the earth precisely,improving the elevation calculation accuracy of stations.Compared with traditional ones,this corrected model could cut down the system offset of estimated wet delay effectively,maintaining the error within mm level.4.A method to obtain troposphere wet delay accurately with surface meteorological data was put forward.A search approach to calculating vertical profile temperature and a piece-wise water vapor pressure model were proposed after analyzing the characteristics of those two parameters on vertical profiles,which could be used to achieve the regional wet delay.5.Estimation method of tropospheric horizontal gradients was put forward based on higher degree Fourier series.A flexible estimation strategy of troposphere delay was brought out after analyzing the varying characteristics of troposphere delay with azimuthal angle,which could guarantee the accuracy and sustain the number of estimates at a low level meanwhile.6.A two-step estimation method of troposphere delay with consideration of mapping function(MF)errors was proposed,which was based on the model of MF errors varying with elevation angles and could reduce slant delay residuals effectively.Also,it would improve the estimated wet delay results.In addition,the method in this dissertation would be helpful to achieving real-time MFs,increasing time resolution considerably compared with VMF series MFs.7.Several issues in VGOS tracking GNSS satellites were studied.First of all,geometric,slew rate and angle distance conditions of network were discussed,when antennas tracking satellites.And then the effects of network distribution,tracking length and orbit errors on the estimation accuracy of geodetic parameters were analyzed.8.Detail researches were conducted on issues,which might be reached during Chinese VGOS site constructions,for instance,observation capability of Chinese VGOS network in future,as well as the capability of network consisting of new and old antennas.In the end,construction progress and testing results of Chinese VGOS site were introduced,with Shanghai site taken as an example.