Study On Sea Clutter Suppression For Shipborne High Frequency Surface Wave Radar

At present,the research and application of land-based HFSWR has been rather extensive.With the economic globalization and the expansion of national interests,landbased HFSWR has limitations.As the evolution of land-based HFSWR,the research of shipborne HFSWR is logical.The main feature for the shipborne platform is the mobility besides inheriting the advantages of land-based HFSWR.Shipborne HFSWR can quickly go to the area of interest to carry out the mission of target detection with this feature.Therefore,shipborne HFSWR has a wide range of development prospect and application value.When a shipborne HFSWR detects ships in the water,sea clutter becomes main interference.The Doppler spectrum of sea clutter is broadened because of the movement of the shipborne platform,which leads to detecting targets difficultly.Now,the study on the sea clutter suppression for shipborne HFSWR is rare,and the related papers are few.In view of the present situation,this thesis will expand the research on sea clutter suppression for shipborne HFSWR and propose more practical sea clutter suppression methods.The main research content of this thesis is as follows:1.First,generation mechanism of sea clutter in HFSWR is introduced.Second,in order to propose better sea clutter suppression methods for shipborne HFSWR,the characteristics of sea clutter for shipborne HFSWR are analyzed,including the spacetime characteristics and chaotic characteristics in sea clutter.However,the characteristic analysis of sea clutter is on the basis of the uniform linear motion of shipborne platform.Three,a novel sea clutter modeling method is proposed using the space-time distribution of sea clutter and considering the three-dimensional movement of shipborne platform at the same time.Four,three-dimensional sea clutter data cubes are constructed,and the modeling method is validated by comparing with the measured sea clutter data for shipborne HFSWR.In addition,the target information extraction methods for two kinds of linear frequency-modulated interrupted continuous wave are introduced.2.Until now,2D FFT plus DBF method,named FFT-DBF,is used commonly to detect targets in HFSWR systems.In addition,it is concluded by analyzing space-time and chaos characteristics of sea clutter,that time-domain sea clutter in any range cell and azimuth cell may be predictable.So a new sea clutter suppression algorithm called PC algorithm is proposed.The time data in all range cells is processed firstly by DBF to obtain the data in the azimuth of interest.After that,the average data in the corresponding azimuth around the range cell of interest is used to train a RBF(Radial Basis Function)neural network.Then,the time data in the range cell and azimuth of interest is used as the input of the RBF network trained.Finally,the differences between predictive values and actual value are processed by FFT to find the Doppler cell generated by the moving target.Compared with FFT-DBF algorithm,the validity of PC algorithm is illustrated by the simulated data and the measured sea clutter data with a simulated target.3.PC algorithm can suppress sea clutter in time domain for shipborne HFSWR.The simplified PC algorithm cannot only suppress sea clutter,but reduce computational complexity.However,they are both one-dimensional methods to suppress sea clutter in time domain.To improve clutter suppression performance,two novel space-time cascade algorithms called IOW algorithm and IOP algorithm are proposed.The IOW approach is firstly to suppress sea clutter in Doppler domain,and then the results of clutter suppression are combined with orthogonal weight method to mitigate sea clutter.The validity of IOW is verified by simulated and measured data.Although IOW can mitigate sea clutter to some degree,the issue of target gain loss exists for IOW algorithm when first-order sea clutter and target are within the same mainlobe.To solve this problem,IOP algorithm is proposed in this thesis,and its principle is similar to IOW algorithm.The only difference is that oblique projection is used instead rather than orthogonal weight.4.To improve the performance of sea clutter suppression further,STAP method is utilized to mitigate sea clutter for shipborne HFSWR.However,the traditional STAP technique needs a large number of samples and has high computational complexity,so it is difficult to use in practice.Thus,a dimension-reduced STAP method named JDL is introduced to suppress sea clutter and is illustrated by simulated and measured data.In addition,an improved JDL named IJDL algorithm is proposed.For IJDL,the time data of all sensors in the range cell of interest is firstly processed by FFT to obtain Doppler cell data.Then,MUSIC algorithm is used to process the data of all sensors in any Doppler cell in the range cell of interest(The samples used in MUSIC are from adjacent data files).The two-dimensional(2D)Doppler-azimuth data can be obtained in the range cell of interest.By the above processing,the 2D data in many range cells can be obtained.Finally,adaptive processing method which is similar to JDL algorithm is utilized to suppress sea clutter.The validity is verified by simulated and real data.