Research On SAR Ship Target Detection And Imaging Method Based On Image Sequence

Synthetic Aperture Radar(SAR)plays an important role in military and civil fields because of its all-time,all-weather and high-resolution imaging characteristics.In recent years,the safety of marine resources and territorial seas has attracted increasing attention from all countries.SAR has distinct advantages in marine monitoring and detection.Geosynchronous SAR(GEO SAR)is a powerful and wide-covered remote sensing system that can achieve long-term beam stationing for observation scenes and targets,and it is suitable for ship detection and tracking.In terms of target detection,parameter estimation,target imaging,etc,the processing methods and strategies of GEO SAR with long synthetic aperture time(up to 100s)characteristic are different from the low-orbit satellite with short synthetic aperture time(usually less than 1s).Therefore,it is important to study target detection and refocusing imaging methods of the ship under the background of GEO SAR observation.The main research contents are as follows:1.The problem of echo simulation and imaging of sea surface and ship target is studied.Based on the target echo model of stationary ship,the model of ship under complex motion is analyzed.Starting from ship target translation and rotation,this paper deduces the range model of ship translation and rotation,and deeply analyses the changes of the range model,Doppler frequency parameters,echo model and the impact of imaging performance.Different from the static statistical modeling of traditional sea surface simulation,a simulation strategy for dynamic modeling of sea clutter in the sea surface coherent time is proposed for the long synthetic aperture time(generally much larger than the sea surface coherent time)characteristic of GEO SAR.And a piecewise dynamic model of sea surface under the long-term observation of GEO SAR is implemented by using linear filter method.The modeling strategy takes into account the accuracy of the statistical characteristics of sea clutter and the computational efficiency of sea clutter simulation.Based on the simulated echo,the problems of moving target SAR imaging are pointed out.2.The influence of ship translation on imaging in the long synthetic aperture time of GEO SAR is studied.A whole process framework with ship detection,parameter estimation and imaging focusing is presented based on sub-aperture image sequence detection.Firstly,the statistical characteristics of sea clutter in GEO SAR sub-aperture images are analyzed by dynamic sea surface simulation.The conclusion that GEO SAR sub-aperture images obey K distribution is pointed out.The performance of constant false alarm rate(CFAR)detection method based on K distribution and IB-CFAR detection method for ship target detection of GEO SAR sub-aperture image sequence is compared and analyzed.Then,the translation parameters are estimated based on the ship target detection results.Finally,according to the result of estimating the ship translation parameters,the range compression data is compensated to achieve the focusing imaging of the ship target.Compared with traditional low-orbit satellites,GEO SAR sub-aperture image sequences provide more free degree for parameter estimation.Therefore,the refocusing performance for target is compared based on GEO SAR sub-aperture image sequences parameter estimation result and based on Doppler offset parameter estimation result.The simulation results verify the validity of the whole processing framework used in this paper.3.The problem of ship target imaging with translation and rotation is further studied.Firstly,based on the geometric model of SAR imaging,the changes of range and Doppler frequency are deduced in theory,and the changes is caused by ship rotation motion.The influence of ship rotation motion on imaging is analyzed by simulation with using ship scattering point model.Then,a SAR-ISAR refocusing imaging strategy based on GEO SAR subaperture image sequence is presented.That is,"Subaperture Image Sequence Acquisition-Translation Parameter Estimation-Translation Parameter Compensation-Refocusing Imaging Result".Based on the above strategies and combined the characteristics of the long synthetic aperture time characteristics of GEO SAR,a processing strategy to improve the resolution of GEO SAR sub-aperture image sequence step by step is proposed.The simulation results verify the correctness and effectiveness of the proposed processing strategy.