Analysis And Application Of Phase Of GNSS Reflected Signal

In recent years,Global Navigation Satellite System Reflectometry(GNSS-R)has developed rapidly.At present,most GNSS-R studies mainly focus on the amplitude characteristics of the reflected signals,but this dissertation focuses on the phase characteristics of the reflected signals.In this dissertation,the reflected signal phase refers to the phase difference of the carrier phase of the reflected signal and the direct signal.In GNSS-R radar remote sensing technology,the carrier phase difference between the reflected signal and the direct signal directly reflects the bistatic range of the target.The bistatic range is closely related to the motion of the object,so it is of great significance to study the phase of the reflected signal.In this dissertation,the phase model of the reflected signal is analyzed systematically,and the application of the phase characteristics of the reflected signal to the enhancement of the signal-tonoise ratio(SRN)of the echo signals and the deformation monitoring are explored.The main research work is as follows:Firstly,the carrier phase models of the direct signal and the reflected signal are derived.And on this basis,the model of reflected signal phase is derived.Under the illumination of Geostationary Earth Orbit(GEO)satellites,by analyzing the phase model of the phase of reflected signal,the phase characteristics of the reflected signals from vessels in different motion states are studied.The theoretical analysis shows that the phase of the reflected signal from a stationary vessel is disturbed near its mean;the phase of the reflected signal from a moving vessel is constantly changing.The experimental results verify this analysis.Secondly,the vessel detection based on the range spectrum,the vessel detection based on the range-Doppler diagram and the enhancement of the signal-to-noise ratio of the echo signal based on the phase characteristics are studied.Vessel detection based on range spectrum can effectively detect stationary vessels.Even if the echo signals of stationary vessel are relatively weak,the stationary vessels can be detected through long-term coherent accumulation.However,this method cannot detect moving vessels with weak echo signals,because long-term coherent accumulation cannot enhance the echo signals of moving vessel.The vessel detection based on the range-Doppler map can effectively detect the moving vessels with weak echo signal,but when the echo signal of the moving vessels is too weak,this method is powerless.In order to solve this problem,this dissertation uses the phase of the reflected signal to derive the relationship between the Doppler and the offset of bistatic range.Then through the spectrum shift in the range direction,the spectrum shift in the Doppler direction and the time-based signal accumulation,the signal-to-noise ratio of the echo signal is enhanced.The experimental results prove that the signal-to-noise ratio of the echo signal can be improved by about 4d B on average after the signal-to-noise ratio enhancement process.Finally,by analyzing the relationship between the deformation and the change of the bistatic range,the relationship between the change of the bistatic range and the phase change of the reflected signal,the relationship between the phase change of the reflected signal and the deformation is determined.The deformation of the object is ultimately measured by the amount of change in the phase of the reflected signal.The experimental results show that the error of this method is less than centimeter level.