Research On Theory And Method Of Tidal Level Monitoring Based On GNSS-MR

The continuous rise of sea level caused by global warming poses a great threat to the national economy and people’s property safety of coastal countries.The effective monitoring of sea level change has become a current research hotspot.In recent years,with the deepening of GNSS research,a GNSS multipath reflectometry(GNSS-MR)remote sensing technology based on GPS multipath effect has been developed internationally.This technology has the advantages of stable signal source,global coverage and low equipment requirements,and is widely used in remote sensing research such as soil moisture,snowfall depth and dam water level.At present,some scholars at home and abroad have carried out the research work of GNSS-MR tide level inversion and achieved some useful research results.However,there are still some urgent problems to be solved,such as low inversion accuracy,low time resolution and single frequency extraction method of reflected signal.Based on this,this paper systematically studies the theory and method of GNSS-MR tide level inversion.The specific work and innovation of this paper are as follows:(1)The GNSS-MR tide level inversion model is constructed,and the basic steps and flow chart of tide level inversion are given;The key technologies of GNSS-MR-Fresnel reflection area,reflection point trajectory,signal separation and Lomb-Scargle spectrum analysis method are systematically studied and analyzed through measured data or simulation experiments.(2)The GNSS-MR tide level inversion experiment of GPS,BDS,Galileo and GLONASS systems was systematically carried out using the measured data of HKQT station.The results show that all GNSS signals can achieve tide level inversion,the inversion accuracy is between 10 cm and 20 cm,and the correlation coefficient is better than 0.92;The longer the wavelength of the downloaded wave in the same system,the higher the inversion accuracy,the greater the correlation coefficient,and the greater the system deviation.(3)Aiming at the low time resolution and accuracy of GNSS-MR tide level inversion,a multi-mode and multi frequency tide level inversion method based on LSSVM is proposed,which is verified by experiments using the measured data of HKQT station.The results show that the RMSE of tide level retrieved by this method is 6.57 cm,the correlation coefficient is 0.9901,the time resolution is 0.478 h,and the accuracy of tide level retrieved is centimeter level,which greatly improves the performance of GNSS-MR tide level inversion.(4)The traditional GNSS-MR uses Lomb-Scargle to extract the reflected signal frequency,which is susceptible to noise interference,the frequency extraction accuracy is low,and the real-time characteristics of the signal cannot be revealed.In order to further improve the accuracy of GNSS-MR tide level inversion,a method of NTFT extracting the reflected signal frequency for tide level inversion is proposed.The experimental verification is carried out using the GPS measured data of HKQT station.The results show that the RMSE of GNSS-MR tide level inversion based on NTFT is0.1044,the mean deviation is-0.0239 m,and the correlation coefficient is 0.9720.Compared with the traditional GNSS-MR,the accuracy improved by 6.30%,the systematic deviation is reduced by 70.92%,and the correlation coefficient increased by0.3%.