Research On Broadband Chirp SAR Imaging Technology Based On Compressed Sensing

Synthetic aperture radar(SAR)is widely applied in the fields of military reconnaissance,resource exploration and environmental assessment.Wideband linear frequency modulation(LFM)signal is transmitted by synthetic aperture radar system to obtain high resolution target imaging.With the increase of transmitting signal bandwidth and the increase of imaging area,the traditional SAR imaging system has been faced many great challenges,such as high sampling rate,large data volume and real-time processing.The compressive sensing(CS)theory,emerged in recent years,has been highly concerned in the field of SAR imaging technology.Based on the characteristics of the signal and the target scattering rate distribution,the sparse model of echo signal is constructed.With the huge advantage of compressed sensing information processing,compressive sensing SAR imaging technology is expected to use a small amount of radar echo data to achieve high-resolution target imaging.Therefore,this theses focuses on the technology of compressed sensing SAR imaging for wideband linear frequency modulation signal.The main research efforts include the sparse analysis of LFM echo signal,the compression measurement method,the reconstruction algorithm and the application of compressed sensing in SAR imaging.The main contents of this theses are summarized as follows:(1)The research of synthetic aperture radar imaging algorithm based on Stretch processing.The two-dimensional representation model of the SAR echo signal is studied,and the high resolution of the range signal and the azimuth signal are analyzed respectively.On this basis,we study the synthetic aperture radar imaging algorithm based on Stretch processing.Simulation experiments verify the feasibility of the algorithm.(2)The research of the sparse representation of SAR echo signal.Aiming at the sparsity analysis of wideband LFM SAR radar echo signal,an orthogonal sparse basis based on Stretch processing and Fourier transform is constructed and then a new form of sparse representation of radar echo signal is proposed.Based on the constructed orthogonal sparse basis,the SAR range signal and azimuth signal are sparsely analyzed respectively,and then the corresponding sparse models are established.(3)The research of the compression measurement method and the signal reconstruction algorithm.Aiming at the compressed measurement method of radar echo,the Analog-to-Information Converter(AIC)is introduced into the compressed sensing SAR imaging system to achieve real-time compression measurement of the echo signal.And the performance of the AIC measurement system is verified by the simulation experiment.Aiming at the reconstruction algorithm,we study three greedy matching reconstruction algorithms of OMP,ROMP and CoSaMP.The performance comparison and screening of the algorithms are carried out by the simulation experiments.(4)The research of compressed sensing SAR imaging for wideband LFM signal.Based on the sparse model of echo signal,compressive sensing processing is done in range and azimuth respectively.Then the SAR two-dimensional imaging algorithm based on compressed sensing is proposed and the detailed process steps of the algorithm are provided.The simulation experiments compare the performance of the taditional Stretch processing method and the compressed sensing method in one dimensional range imaging and two-dimensional SAR imaging,and verify the effectiveness and superiority of the imaging algorithm based compressed sensing.