Research On Sea Surface Target Detection Method Under Airborne Radar

Airborne radar can achieve large range and long distance detection by virtue of its own mobility,flexibility and the height advantages,so it has a wide range of applications in both military and civilian.However,airborne radars usually observe the sea surface at medium and high incident angles,which increases the energy of sea clutter.On the other hand,due to the motion of the carrier,the radial velocity is generated between the sea clutter and the carrier,and the sea clutter will produce a doppler frequency shift.In addition,the transmitting beam has a width,so that the radial velocity between the sea clutter and the radar in different directions is different,which causes the doppler spectrum broadening.Therefore,the airborne radar underwater clutter will have radial velocity expansion,which will increase the probability that the target will be submerged by sea clutter,leading to the performance degradation of conventional constant false alarm detection and adaptive matching algorithm.In view of this situation,this thesis starts with the simulation of airborne radar sea clutter,then airborne radar sea clutter suppression and target detection is performed on the basis of sea clutter property analysis and feature extraction.Specifically speaking,the main content of this thesis is summarized as follows:1.The first part focuses on simulation and characteristic analysis of airborne radar sea clutter.First,according to the space geometric configuration of the airborne radar,the expression of the doppler frequency of the sea clutter under the forward-looking array is derived,and it is found that the space-time coupling relationship of the sea clutter under the forward-looking array is nonlinear.Then the total echo power is calculated according to the divided scattering units,and finally the space-time 2-D sea clutter data is obtained.The simulation results show that when the pulse repetition frequency(PRF)of the radar is very low,the simulated sea clutter will produce ambiguity on doppler frequency;when the radar works in high PRF mode,the sea clutter will produce range ambiguity.On the other hand,the operating wavelength of the radar is longer,the echo power of the sea clutter generated by the simulation is greater,and the doppler spectrum broadening of the sea clutter is smaller.In addition,the characteristics of the sea clutter measured by the airborne radar are analyzed.The simulation results show that the airborne radar sea clutter obeys the K+Rayleigh(KR)distribution,and the time-frequency domain characteristics such as time-frequencyspectrum Shannon entropy and time-frequency aggregation can well distinguish between sea clutter and target.2.The second part focuses on sea surface target detection algorithm of airborne radar,the detection algorithm based on joint feature is proposed.Firstly,the feature is extracted from the pure sea clutter data,and then the feature dimension is reduced by principal component analysis.Secondly,the convex hull learning algorithm is used to calculate the detection decision region of the reduced feature vector.Finally,the feature vector of the sample to be tested is detected.If all the feature points fall within the detection decision region,it means that there is no target,otherwise,there is a target.The experimental results show that the multi-feature joint detection algorithm can not only realize the target detection on the sea surface,but also the detection probability of this algorithm is significantly higher than that of the conventional algorithm under the same signal-to-clutter ratio.3.The third part focuses on the sea clutter suppression and weak target detection algorithm.When target detection is carried out under the background of strong sea clutter,target echo is likely to be submerged by sea clutter,so sea clutter suppression is needed.The proposed suppression algorithm mainly uses singular value decomposition to project the Hankel matrix of sea echo into the target subspace.The experimental results show that singular value decomposition can suppress sea clutter and improve signal-to-clutter ratio,which is beneficial to detect target.Then,a detection algorithm based on the corss S-Method is proposed for detecting weak target on the sea surface.Firstly,the CSM of the signal is calculated.Secondly,the cross Wigner-Ville distribution inverse transform is used for timefrequency decomposition on the basis of singular value decomposition.Finally,the timefrequency aggregation of the decomposed component is used to determine whether it is the target signal component.The experimental results show that the algorithm can not only realize the detection of weak target on the sea surface,but also display the instantaneous motion state of the target.