Research On Sea Surface Moving Target Imaging Algorithm Based On Phased Array Airborne SAR

China is a large marine country,the detection of ship targets at sea is not only related to our economic interests,but also related to the sovereignty of national lords and coastal defense security.Phased array airborne synthetic aperture radar uses the spatial structure of array antenna to increase the spatial dimension sampling frequency and enlarge the range of surveying and mapping zone in the sea area,which makes it possible to image ship targets in wide area with high resolution.At present,there are some problems in phased array airborne SAR,such as complex antenna array structure,large amount of data processing and ship target imaging defocus,which affect the imaging efficiency and quality of moving targets in wide area.Therefore,this paper focuses on the phased array airborne SAR moving target high resolution imaging algorithm,and deeply studies the antenna beam scanning mode,multi-antenna receiving data processing algorithm,moving target Doppler parameter estimation and time-frequency analysis algorithm.The main work of this paper can be summarized into the following five parts:Firstly,Aiming at the selection of imaging scanning mode of phased array airborne SAR,range pitch scanning and azimuth scanning are used to image wide swath scene respectively.Firstly,the phased array airborne SAR imaging model is established based on the wide swath scene.Under the condition that the pulse repetition rate of the transmitted signal is limited,the signal processing process is deduced through the theoretical formula,and two imaging models of DBF-SCORE mode and TOPS mode are built.Then,through simulation experiments and measured data imaging,it is verified that the above two modes can realize range beamforming high resolution imaging and azimuth wide amplitude fast scanning imaging respectively.The scanning mode of phased array SAR beam control is clarified,which lays a foundation for the follow-up research of wide area sea surface imaging algorithm.Secondly,Aiming at the difficulty of massive data storage and operation in the process of phased array airborne SAR wide area sea surface ship imaging,starting with the sparse attribute of ship target distribution,a block sparse compressed sensing moving target imaging algorithm is proposed in this paper.Firstly,based on the traditional greedy OMP algorithm,the sea ship compressed sensing imaging algorithm model is built.The simulation results show that the ship meets the target sparse characteristics,and the compressed sensing algorithm can be used for imaging.Then,using the diversity gain of antenna array and the block sparse distribution attribute of ship target,a joint block sparse compressed sensing imaging algorithm is proposed.The imaging results of simulation and measured data show that a more unified target distribution can be obtained by using the block sparse class algorithm,which can greatly reduce the imaging time of the panoramic area and help to eliminate the false targets on the sea surface.Thirdly,Aiming at the problem of image defocusing and blurring caused by ship motion,a Doppler parameter estimation So WVD algorithm is proposed.Firstly,the influence of Doppler parameters on the imaging effect is analyzed,and the Doppler parameter signal estimation model is built.The simulation results show that the traditional algorithm is helpful to correct the range migration and compensate the azimuth phase error related to the range space variation,but the operation time is not suitable for real-time estimation.Then,in order to reduce the computational complexity,a Doppler parameter estimation So WVD algorithm is proposed.Simulation experiments verify the effectiveness of the algorithm.Compared with the traditional parameter estimation algorithm,So WVD algorithm is suitable for real-time Doppler parameter estimation of small targets such as ships by phased array airborne SAR.Fourthly,Aiming at the problem of image defocusing blurring under the three-dimensional swing of yaw angle,pitch angle and roll angle,on the basis of moving target self-focusing and time-frequency analysis algorithm focusing imaging,a synchronous compression time-frequency transform algorithm is proposed.Firstly,the maximum contrast / minimum entropy self-focusing iterative algorithm and block PGA focusing algorithm are used to further focus the blurred images of several ships in the measured data.The imaging results show that the algorithm can reduce the sea clutter sidelobe and sea surface virtual shadow very well.Then,the SAR/ISAR hybrid imaging model is built,the instantaneous time-frequency imaging of a single ship is carried out by using the traditional time-frequency analysis algorithm,and the synchronous compression time-frequency transform operator is introduced to obtain the focus image of the swinging ship at a certain moment.Through the comparison of the simulation experiments and the measured data performance parameters,it can be known that the synchronous compression algorithm can counteract the image defocus and blur caused by ship swing,obtain high-definition ship image,and can see the ship structure,size,bow,stern,side and other detailed parts..Fifthly,Aiming at the problem of positioning error of the moving ship,a VSAR algorithm for correcting the azimuth position of moving target is proposed by making use of the balanced distribution of antenna array structure.Firstly,the reason of azimuth position error of sea surface ship with radial velocity is analyzed,and the mathematical expression of azimuth position error is deduced.Then,the VSAR algorithm model is built,and the real position estimation of radial velocity and azimuth of the target is obtained by analyzing the phase difference of the data received by the antenna array.The simulation experiments and measured data verify the feasibility of the algorithm.he Imaging results show that the VSAR algorithm can observe the moving targets continuously and dynamically,effectively distinguish the static and dynamic targets in the Doppler band,and improve the ability to judge the trend and trajectory of the ship.