Analysis And Processing Of The First-order Sea Echo Observed By Shipborne Hf Surface Wave Radar

High frequency surface wave radar(HFSWR)can be used for over-the-horizon,wide-range and all-time remote sensing in specific sea areas,which is a good choice for measurement of the ocean surface wind,wave and currnet,detection and tracking of ships or low-altitude flying targets as well.Be compared with HFSWR system used large aperture antennas,a portable system has the features of small,less occupied area,easy for installation and maintenance,can also achieve good angular resolution via super-resolution algorithm.HFSWR can be divided into shore-based and shipborne according to different setup locations.Besides the characters inheriting from the shore-based radars,shipborne radars can expand detection range,improve environmental adaptability,monitor the ocean more flexibly.Therefore,the shipborne portable HFSWR has great advantages and application prospects for civil or military use.Exploratory experiment in Fangchenggang,has been accomplished by Radar and Signal Processing Laboratory(RSPL),Wuhan University,to research sea echo characteristics,the performance of ocean parameters extraction and target detection.Based on this shipborne experiment,this paper make a theoretical research and measured data processing on the expansion mechanism of the first-order sea echo,the inversion of the radial current field and the wind direction,the suppression of stretched sea clutter,and achieved some results.The main research work of this paper is listed as follow:1)This paper analyzes the effect of ship velocity,current,wind direction and radar aperture angle on the first-order sea echo spectrum with a shipborne detection model by an underway method,and explains the reasons why the Doppler spectrum of shipborne test is different from shore-based radar.2)Discussing the feasibilities of radial current extraction,detailing the principles and results of every processing steps.Current velocity and azimuth distribution are consistent with the theoretical model,the inversion results of the radial current field are given at last.Based on the characteristics of Doppler spectrum changes with wind direction,a new method of wind direction estimation is proposed,the problem of ambiguous wind direction in monostatic radar is solved,and the estimation result agrees well with the actual wind direction.3)In order to suppress the sea clutter,the performance of a single monopole cross-loop antenna in shipborne radar is studied by space-time adaptive processing,a method based on spatial decomposition is proposed.This method can inhibit the stretched sea echo and highlight the targets,while it makes the target azimuth change.To this end,the methods of adding an adjustment factor or antenna element,compensating the steering vector is proposed to eliminate this effect.