| As an important part of the Earth's atmosphere,the troposphere is often inseparable from the formation of various weather events and climatic phenomena.The temporal and spatial changes of tropospheric water vapor are active,and conventional atmospheric detection methods are difficult to capture its spatial and temporal distribution characteristics.Ground-based GNSS technology has gradually become one of the most promising detection means in modern meteorological applications,with the advantages of high precision,high temporal and spatial resolution,and all-weather observation.This thesis focuses on the ground-based GNSS technology.We firstly learn and understand the theoretical knowledge of ground-based GNSS combined with PPP technology for retrieving tropospheric water vapor,and triumphantly invert the tropospheric water vapor by using the Bernese software,and then we obtain the three-dimensional distribution information of water vapor based on GNSS water vapor tomography software.Furthermore,we initially explore the global climate change characteristics with the long-term tropospheric products provided by CODE,all of them laid the foundation for the application of ground-based GNSS technology and theory to modern meteorological systems and climate monitoring.The main research work and achievements of this paper are as follows:(1)In the aspect of ground-based GNSS technology for detecting two-dimensional water vapor,we analyze and reveal the accuracy difference of water vapor inversion of single GNSS PPP technology and the performance improvement range of combined positioning,and the globally distributed MEGX tracking station data is used to carry out GNSS retrieval experiment of atmospheric precipitable water.Taking the CODE tropospheric products and Radiosonde observations as a reference,we carefully compare and analyze the ZTD and PWV results obtained from individual GNSS and multi-GNSS,and the performance of multi-GNSS data for ZTD/PWV retrieval is also assessed.The results reveal that the accuracies from different individual GNSS results are different,the accuracy of multi-GNSS combination can obtain the most robust water vapor sequence results.Meanwhile,compared to the GPS,GLONASS,Galileo,and BDS single GNSS results,the multi-GNSS ZTD results are improved by 10.91%,19.04%,33.21% and 70.16%,respectively,and the multi-GNSS PWV inversion accuracy improved by 3.45%,16.16%,16.45% and 41.78%,respectively.(2)According to the basic principle of ground-based GNSS technology for 3D water vapor,a set of ground-based GNSS three-dimensional water vapor chromatography software was written in C++ language.In order to solve the problem of low utilization rate of GNSS signal in traditional tomography experiments,we design and implement a multi-GNSS water vapor tomography method which takes into account the boundary incident signal,and which uses the 12 station data and the sounding product from the Hong Kong SatRef.The experimental results show that compared with the traditional GPS tomography method,the introduction of multi-GNSS combination signal and boundary incident signal can increase the number of effective observation data,improve the space rate by 4.2% and 17.22%,improve the overall accuracy by 1.79% and 7.00% on MAE,and improve the RMS by 1.41% and 7.46% respectively.The new water vapor tomography method fusing the two kinds of signals has the most effective observation number,with an average space rate.The improvement was 21.01%,with 8.22% and 9.13% accuracy improvement on MAE and RMS respectively.(3)The tropospheric parameters of globally distributed GNSS stations are used to explore climate change characteristics based on the 13-year tropospheric resolving products provided by CODE.At fisrt,we analyze the consistency of the tropospheric parameters between the co-location GNSS station,it is found that the replacement of the receiver antenna type will mostly destroy the stability of the long-term sequence.For this reason,we then count the number of the antenna type replacement of each station and introduce a method to correct the ZTD deviation,and the results show that the method has obvious correction effect on the deviation caused by the antenna type replacement.In the subsequent tropospheric product time series analysis,we analyze the global cyclical information of atmospheric water vapor and its spatial correlation based on the information obtained from the ZTD and horizontal gradient sequences,such as the annual average,annual amplitude,initial phase and the trend changes,and so on,and we find that atmospheric water vapor changes and water vapor circulation flow are in the state of global balance. |
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