A method to establish the tomography model considering the data of GNSS stations outside the research area

To overcome the phenomenon of the traditional tomography technique that cannot use the data of GNSS stations outside the research area, a novel three-dimensional water vapor tomography modeling considering the data of GNSS stations outside the research area is proposed. The initial water vapor field of tomographic area in each voxel was calculated based on the GPT2w model. The proportional coefficient is introduced and combined with the initial value of water vapor density to determine the proportional coefficient expression. The water vapor content of the signals in the tomography area from the stations outside this area is estimated. Finally, the water vapor observation equation considering the data from the GNSS stations outside the tomographic region is established. The proposed method can be used to utilize the GNSS observation efficiently and improve the accuracy of tomographic result, but it only validated to the GNSS stations located in a certain range outside the tomographic area. Twenty-four GNSS stations and one radiosonde station in Zhejiang CORS network were used to verify the proposed tomography model in this paper. The experimental results show that compared with the traditional chromatography method, the utilization rate of GNSS signals and the voxel number with signals passing through are increased by 26.8% and 14.9%, respectively. Taking the radiosonde data as reference, it is found that the accuracy of integrated water vapor and water vapor density profiles calculated by the proposed method are better than those calculated by the traditional method