| High Frequency Surface Wave Radar(HFSWR)utilizes the advantages of that propagation attenuation of(3-30MHz)radio wave will decrease when propagating along the ocean surface to carry out targets detection,marine remote sensing over the horizon and all-weather.According to different radar system installation platforms,HFSWR can be classified as shore-based HFSWR and sea surface floating platform HFSWR.With the successful development of shore-based HFSWR system and the launching of testing experiments on the sea at home and abroad,the shore-based HFSWR technology becomes more and more mature and has widely used in target detection at sea and ocean dynamics parameters remote sensing detection.Due to the attenuation of electromagnetic wave along with distance,the detection of the shore-based HFSWR is limited in far ocean area.However,the sea surface floating-platform radar extends the application of HFSWR technology and break the constraints of the shore-based HFSWR.Floating-platform surface wave over the horizon radar can flexibly detect the ocean area of interest by advantage of platform movement and erection on the sea surface.It can also be used as a detection node to build the integrated network with shore-based radar through the distributed synchronization technology so as to realize target detection at sea and ocean dynamics parameters remote sensing detection of larger ocean area.Therefore,the floating-platform radar has broad prospects for development and application in military and civilian.However,due to the complexity of floating platform motion in this mode,there are still some problems in the process of radar echo signal processing.Based on the National 863 plan key project,Wuhan University sea state laboratory and its related cooperation organizations carried out the test experiment of floating-platform radar on the ocean,which greatly promoted the application and development of the floating platform HFSWR.This paper studies the radar echo signal preprocessing method of floating platform on the sea,which is an important part of the radar signal processing of the project.The research results provide a new idea and method for the study of radar sea state remote sensing on the sea surface floating platform.The main research contents are as following:1.The system composition,working mode and signal waveform system of the floating-platform radar are introduced in this part.In order to make full use of the space area of the platform,a uniform circular receiving array is designed and its radiation/reception performance is analyzed and simulated.Considering the move-ment of the floating platform with time,a simple motion model is established based on the relationship between six degrees of freedom motion of the platform and the receiving array,and the influence of floating-platform's movement on the array signal processing is analyzed.2.Two kinds of direct wave calibration algorithms are introduced,namely getting the eigen-value of direct wave signal based on covariance and getting phase difference of each antenna directly from direct wave.In the integrated network combined with floating-platform radar and shore-based radars,each shore-based radar station can receive more than two radar stations direct wave signals.A Double-preferred method for getting amplitude and phase calibration value is proposed to provide more accurate calibration values for channel matching of shore-based radars.Based on the floating platform motion model,the main factors affecting the amplitude and phase calibration are analyzed and rotation motion of platform and distortion of radiation pattern in receiving antenna array predominate.Thus a piecewise calibration method for floating-platform radar is proposed to compensate the rotation motion and the distortion of the antenna radiation pattern.The validity of the method is verified by the measured data and the estimated direction of arrival.3.The first-order scattering cross section equation of the radar system receiving platform yaw motion is studied,and the characteristics of the first order spectrum region of radar single-base and bistatic mode are analyzed.The traditional first-order spectral region division method and implementation flow are briefly introduced.In general average-smoothing difference spectrum method,the problem of selecting a smooth number of points and causing a large deviation of the dividing result is proposed.This paper proposes a least square approximation fitting function method based on the characteristics of the first order spectrum-peak.Altering bistatic angle in every range cell in bistatic mode,the maximum search boundary for each range is confirmed dynamically.The least square method and the incorporation of the altering bistatic angle factors into the bistatic division method are verified to be valid and rational by the division results based on the measured radar data in this paper. |
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