GNSS Multi-frequency And Multi-mode Reflected Signal Characteristics And Its Inversion At Water Surface Height

As the most intuitive factor reflecting the water regime,water level is of great significance to the study of water cycle,ecological changes in water areas,and the protection of life and property safety of residents around water systems.Traditional water level monitoring measures water level through water level gauges installed in tide gauge stations or hydrological stations,but the measurement results are relative results jointly affected by crustal deformation and water level changes,and are greatly affected by regions.With the rapid development of the global navigation satellite system(Global Navigation Satellite System,GNSS),GNSS-R(GNSSReflection)technology based on GNSS reflection signals also provides new ideas and methods for water surface height measurement,especially At this stage,large domestic projects such as the Three Gorges have established a large number of GNSS-based automatic deformation monitoring systems on high-risk slopes and dams,which can provide a large number of longterm monitoring systems for the application of GNSS-R technology in water surface surveying.Stable and high spatial-temporal resolution data not only expands the application scope of GNSS data,but also greatly reduces the cost of water level measurement,and lays a rich data source for GNSS-R water surface inversion in theoretical research and practical application.Based on the detailed elaboration of the basic principles of GNSS-R water level inversion,this paper focuses on the optimal station layout of GNSS-R in the survey area and the refined extraction of reflected signals to carry out the theory of multi-frequency and multi-mode joint inversion of water surface height Method and experimental verification research,the main research content and results of the paper include:(1)On the basis of studying the theory of GNSS reflection signal water surface height inversion,the overall process of GNSS-R technology water surface height measurement is given,and the signal-to-noise ratio data performance under multi-frequency and multi-mode signals and the reflection signal based on signal-to-noise ratio are given.An overview of extraction methods and their advantages and disadvantages in application.(2)In order to maximize the temporal and spatial resolution of GNSS-R station inversion data,the inversion event is defined by parameters such as effective reflection area and satellite elevation angle threshold,and a method is given based on the operating characteristics of the satellite and the geographical location of the station.GNSS-R station space-time layout optimization strategy.Through the analysis and experimental verification by simulating the middle and low latitude stations in the northern hemisphere,the results show that this strategy can effectively provide the optimal position and observation period of GNSS-R in the survey area,so as to be applied in waters with more geographic locations.(3)In order to improve the utilization rate and accuracy of the inversion results,the adaptive characteristics of the empirical mode decomposition method in signal decomposition and reconstruction are used to fine-tune the reflection signal extraction and further optimize the GNSS-R technical process.By selecting the sea surface for experimental verification,even for the water surface with large fluctuations,the inversion results obtained by the optimization method are obviously better than the classical method,and while ensuring the inversion accuracy is improved,the utilization rate of the inversion data is also greatly improved.(4)The GNSS-R station layout strategy and reflection signal extraction optimization method proposed in this paper are further verified by selecting the measured data in typical waters.In particular,using the observation data of GPS,BDS,and Galileo in a total of 9frequency bands,the single-frequency inversion results and multi-frequency joint inversion results under the multi-frequency and multi-mode mode are given.The results show that the refined reflection signal extraction After multi-frequency and multi-mode joint inversion,the accuracy and time resolution of the final results are better than those of single-frequency singlesystem,which has important reference significance for the practical application of GNSS-R.