Regional Precision Tropospheric Delay Modeling

Tropospheric delay is a major error source of GPS survying. It can be reduced by differential method in short baseline measurement, However, the residual tropospheric delay is still the main error sources of precise surveying (such as deformation monitoring) when the height difference of baseline is large or the weather is fluxible in small region. In practical applications, empirical tropospheric delay model which need to enter the meteorological parameters is used to correct the errors, but the errors of the meteorological representativeness is introduced, so the accuracy of actual correction is not high. In this paper, the effects of height difference and the horizontal change of troposphere on the accuracy of GPS surveying is discussed at first. And then GPS observation data collected in several years from Hong Kong Continuously Reference Station Network is used to build the precise tropospheric delay model. This model is based on estimated zenith tropospheric delay of all the stations using the Bernese GPS software. The input parameters of the model are day of year and location of the station. The main achievements and specific research work of this paper are as follows:1. The atmosphere effect on GPS measurement, especially the reasons of the tropospheric delay is analyzed and then some methods to reduce the error are summarized. After that, some common empirical tropospheric delay correction models are compared.2. The residual tropospheric delay effects on GPS surveying caused by the height difference is analysized in detail based on the results from commercial GPS data processing software. In order to study on the residual troposphere delay variation with height difference, the Bernese software is also used to estimate zenith tropospheric delay. The results show that:in the hot and humid weather, the residual tropospheric delay error will vary with the increase of height difference if only standard meteorological elements and empirical model correction are used in baseline processing. 3. The baselines with different length but small height difference are calculated by a commercial GPS software and Bernese GPS software respectively. The regional tropospheric delay effects by horizontal varivation on GPS measurement was analyzed, the results show that: when the baseline is less than 15km, the residual tropospheric delay is not large. If the length between 15km and 30 km, the residual tropospheric delay effects on GPS measurements become significant. While the length close to or more than 30km, the residual tropospheric delay will become larger in hot and humid weather, and that the result is baseline solution often failed.4. Four years zenith tropospheric delay of 12 stations in the CORS network of Hong Kong estimated by Bernese GPS software this paper. And the precision troposphere model correspond the Hong Kong region has been established based on the results. The input parameters of the new model are only time and location. After testing, the average accuracy of the new model determine absolute zenith tropospheric delay is about 2cm, and the correction effect of tropospheric delay with large height difference is remarkable, the precision of determination of the relative tropospheric delay compared Saastamoinen model with standard meteorological parameters increased by about 2 to 3 times, the accuracy of height measurement will increase 4 times too. The new model not only can be applied to ordinary precise surveying of short-baseline but also can highly popularized in sub-meter level navigation and positioning applications.