Retrieving Water Surface Height With High Accuracy And Reliability Based On GNSS-R And Its Validation

The change of water surface height has a significant impact on climate,environment and human survival.In the context of global warming,the rising trend of ocean tide level and inland reservoir water surface height has brought security risks to human society,so how to effectively monitor the water surface height and predict its rising trend has become a hot issue in current research.However,traditional water surface height monitoring methods have low spatial and temporal resolution,difficult to guarantee accuracy,reliability and availability under complex terrain and bad weather conditions,high power consumption and high measurement cost.In recent years,the Global Navigation Satellite Systems-Reflectometry(GNSS-R)technology has been widely used in water surface height inversion,which not only provides long-term stable and high spatial and temporal resolution signals,but also can effectively use many shore-based IGS stations in coastal areas and The GNSS deformation monitoring system established by large and medium-sized dams and high slopes of reservoir banks provides hardware equipment and rich data resources without repeated construction,which has become one of the hot research areas for experts and scholars at home and abroad.However,in the current research,especially in China is still mainly in the initial stage of GNSS-R technology water surface height inversion theory and application research,still need to refine the reflection signal extraction and other key issues for in-depth research and solution.In order to make full use of the data from the existing sea-based IGS stations and the GNSS deformation monitoring system on the shore of reservoirs and dams,so as to reduce the cost of water surface height monitoring,as well as to improve the temporal resolution and accuracy of water surface height change monitoring.This thesis focuses on the basic principle of GNSS-R for water surface height inversion,based on which the key issues of refined water surface height inversion are studied in detail,the software development is realized based on the principle,and the reliability and effectiveness of the algorithm are verified by the measured data.The research contents and results of this thesis specifically include.(1)Detailed derivation of the principle of GNSS-R refinement of water surface height inversion,focusing on the method of refinement of extracting available inversion satellites and their effective time periods,and on this basis,the trend term removal and Lomb-Scargle spectrum analysis are completed to give a complete data processing flow of inversion of water surface height.Then the signal-to-noise ratio and its characteristics are introduced,and the correspondence between signal-to-noise ratio and multi-path in the low altitude angle range is discussed in depth.And the key issues of refinement of water surface height inversion of GNSSR technology,such as satellite signal reflection point trajectory,the Fresnel reflection region,SNR residual sequence refinement extraction and Lomb-Scargle spectrum analysis,are discussed in detail.(2)The "GNSS-R refined inversion water surface height data processing software v1.0" is developed in the MATLAB environment,and the technical route of the software is given and its basic functions are introduced.The basic functions of the software were tested with GNSS observation data,and the feasibility and validity of its application to the inversion of water surface height were verified,and the results showed that the GNSS-R technology can accurately obtain the water surface height.Development of the software alleviates the huge and complicated data processing work in water surface height change monitoring,and improves the monitoring efficiency.The progress of the software provides data support for the processing of subsequent experimental data.(3)The experiments were performed by selecting the actual data from reservoirs with small water surface variation and ocean shore stations with large water surface variation.Firstly,the actual measurements were made in the reservoir,and the inverse water surface height was compared with the actual measured water surface height for analysis.The results show that the inversion accuracy of both different stations reaches the centimeter level,which meets the general water surface height monitoring need.In order to further verify the reliability and accuracy of the algorithm in complex environments,another tide level monitoring experiment was carried out with the data from the marine shore-based stations,and correlation analysis was performed with the data from the neighboring tide gauge stations to verify the feasibility and effectiveness of GNSS-R technology in reservoir water surface height and tide level monitoring.