Research On Significant Wave Height Inversion Method Based On Ship-borne GNSS-R Delayed Doppler Maps

In recent years,Global Navigation Satellite Systems Reflectometry(GNSS-R)technology has become an emerging technology for the development of marine remote sensing.GNSS-R technology can invert and reconstruct multi-objective and multi-dimensional feature information in data images.In many research fields such as ocean remote sensing and global meteorological observation,significant wave height is an important parameter to describe the sea state of a specific sea area.Based on the global navigation GNSS-R technology,this thesis proposes an effective wave height inversion method using delay Doppler images.Using GNSS-R technology to achieve high-precision inversion of sea surface significant wave height is of great significance for marine environmental monitoring and marine disaster prediction.Firstly,this thesis introduces the conventional navigation satellites in Global Navigation Satellite Systems(GNSS),and analyzes the geometric principle,signal characteristics and sea surface scattering principle of GNSS-R technology in detail.In this thesis,a ship-based GNSS-R significant wave height measurement experiment was deployed and implemented by a miniature L-band marine environmental dynamic detector and Oceanpal receiver mounted on the ’ Yukun ’ teaching ship.On the basis of this experiment,this thesis further introduces the functions and overall architecture of the GNSS-R hardware receiver related modules used in the experiment,including the simulation design principle of the satellite signal receiving antenna and the design and construction of the Doppler delay mapping receiver.Secondly,by studying the traditional model Interferometric Complex Field(ICF)based on GNSS-R inversion of significant wave height,it is found that coherent integration filters out the high-frequency components of ICF function,resulting in large inversion error of ICF-based inversion method in open sea conditions.In this thesis,a delay Doppler image is generated based on the reflected signal,and the definition of signal-to-noise ratio is given.On this basis,this thesis proposes an effective wave height inversion method based on signal-to-noise ratio,and verifies the feasibility of the algorithm through ship-borne experiments.Although the inversion method based on signal-to-noise ratio proposed in this thesis solves the problem of limited inversion of ICF algorithm in offshore waters,the algorithm mainly uses the average value of correlation power after fitting,which is also affected by signal noise.Therefore,how to fully invert and characterize the significant wave height remains to be further explored.Finally,based on the relationship between the length of one-dimensional delay-dependent power delay window and the effective wave height,a model based on delay window to invert the effective wave height is designed.In the data processing stage,clustering and data cluster morphology analysis are used to further improve the accuracy of fitting.In order to obtain a more stable and accurate effective wave height inversion model,this thesis has made innovations in data screening and algorithm :(1)In this thesis,the delayed Doppler image is generated by the reflected signal,and the corresponding definition of signal-to-noise ratio is given.Therefore,an effective wave height inversion method based on signal-to-noise ratio is proposed.(2)In this thesis,a model of effective wave height inversion based on time delay window is proposed for the first time,which realizes more accurate effective wave height inversion,breaks the inherent mode of traditional inversion model,and provides a new research direction for effective wave height inversion.(3)In the aspect of data filtering,in order to make the data fitting avoid too much influence of outliers,this thesis further processes the data by clustering and data cluster morphology analysis.In the one-dimensional correlation power and time fitting curve of the reflected signal,since the correlation power is greatly affected by the fitting,the ICF model and the SNR model have large errors.In this process,the delay window scale is less affected by fitting and more stable.In order to verify the feasibility and robustness of the inversion model,this thesis compares the inversion data obtained by the three models with the measured data of the nautical seismometer,and finds that the model structure based on the time delay window is the simplest and the inversion accuracy is higher.This thesis confirms that the significant wave height inversion model based on time delay window has great reference and application value for the monitoring of sea state information.