Study On Novel Inversion Algorithms Of Ocean Wave And Current Parameters With Marine X-band Radar

There is some information about sea surface other than moving vessels and reefs in the Marine X-band radar image sequences.By analyzing the continuous image sequences,high-resolution ocean wave and surface current information can be calculated using corresponding inversion algorithm.Now,the marine X-band radar has been widely used in monitoring systems for obtaining wave and current information.Two novel inversion algorithms of ocean wave and current parameters with marine X-band radar have been presented and realized.At the beginning of this dissertation,the research background and research significance are briefly introduced.The history and recent status of the research on ocean remote sensing using marine X-band radar are also summarized.Then,the imaging model and modulation by marine X-band radar are presented.For further research,a wave and current monitoring system based on marine X-band radar,with independent intellectual property rights,was developed by radio oceanography laboratory at Wuhan University.A set of software for the monitoring system was also developed using C++ Builder under Windows system.Based on the study of the conventional inversion algorithms based on FFT and shadowing respectively,we introduce the whole process of the two conventional algorithms in detail.Some improvements and innovations have been taken into the two conventional inversion algorithms.Shadowing recongnition is one of the key steps in the conventional shadowing algorithm.An improved shadowing recongnition based on image segmentation that increases retrieval efficiency and accuracy is proposed.The model of this conventional shadowing algorithm has been detailedly analyzed and discussed,and a correction term for the 1-D illumination model is presented.After introducing the conventional algorithms,two novel inversion algorithms have been presented.A new shadowing algorithm for retrieving SWH based on inverse fast fourier transform(IFFT),one of the two novel algorithm,is shown in the paper.This algorithm abandons the 1-D illumination model.A new image sequence is obtained by the IFFT of the filtered wave directional spectrum,and a series of shadowing modulations based on the different setting SWH values is taken in the new image sequence.Then,shadowing modulation results are matched with the shadowing recongnition result from the original image sequence,so SWH can be estimated.The other new algorithm using array beamforming for estimating waves and currents from marine X-band radar image sequences is also proposed,which is differ from the conventional algorithm.Array beamforming is used to extract the wave directional spectrum from the image sequences;the image intensity time series is considered as the signal received by the "antennas" in conventional array beamforming.To retrieve the current velocity,the following feature is utilized:the total power reaches a maximum when a suitable current is used in the beamforming calculation.Because the new algorithm is based on individual pixel points,as opposed to the full image in the conventional method,the coordinate transformation procedure can be avoided.Because of the filter capacity in beamforming,moving vessels and shadowing have little effect on the estimate results,and the empirical modulation transfer function is not required to amend the wave spectrum.The wave and current retrieval scheme is validated using a simulation.Finally,the above algorithms are validated by the seaside field experiment.The radar data from in Zhou Shan,China,on January 2014,are processed by the above algorithms.Estimate results are compared with the data from the in-situ buoy.The satisfactory inversion effects show values of reliability,practicability and application in the above algorithms.At the end of the dissertation,a summary and prospect on the new algorithms are made.