Study On 3D Imaging Algorithm For Highly Squinted SAR

3D SAR imaging extends the conventional 2D SAR imaging technology by forming a new synthetic aperture along the elevation direction.The 2D SAR image that is the projection of the real world on the imaging plane is obtained by making two-dimensional matching filtering of the echo signal,and the focused value of each range-azimuth cell is the integral of the reflected signal from the scattering points at different height.The geometric distortion such as overlay,shadow and telescope results in the loss of real 3D information.The 3D SAR imaging system can reconstruct the 3D observation scene,in addition to the rangeazimuth resolution ability,but also can determine the distribution of scattering points at different height.The 3-D imaging technology has wide range of applications in 3D topographic mapping,forest monitoring and missile guidance.Developing 3D imaging technology has become an urgent requirement in the field of SAR technology.In this paper,two 3D imaging techniques,tomography SAR and curvilinear SAR,are studied.The specific work of my dissertation is as follows:The basic principles of SAR imaging are studied,and the causes of various geometric distortions are analyzed in combination with the fuzzy model of two-dimensional SAR.The basic principles of SAR imaging are studied,and the causes of various geometric distortions are analyzed in combination with the fuzzy model of two-dimensional SAR.According to the imaging geometry and echo model of SAR,the method of obtaining distance and azimuth high resolution and the causes of distance migration are analyzed.The classical frequencydomain and time-domain imaging algorithms are simulated.Using the cylindrical symmetric fuzzy model of 2D SAR imaging,the causes of geometric distortions such as overlay,telescopic and shadow are analyzed.These work lays a theoretical foundation for the subsequent extension from 2D SAR imaging to 3D SAR imaging in this paper.The 3D imaging method for high-squint tomography SAR is studied,and the superresolution 3D imaging algorithm for front side view mode of the mobile trajectory is proposed.By analyzing the echo of tomography SAR,the current 2D SAR imaging is extended to 3D SAR imaging.The three-dimensional spatial-variant coupling of rangeazimuth-height direction is eliminated by time-domain imaging algorithm,and 3D imaging is decoupled into two-dimensional imaging and tomography focus.The focus method of tomography is focused on.The results show that tomography signal and the height of scattering point is a Fourier transformation relationship,and the NUFFT algorithm can achieve good tomography focus effect for the echo of non-uniform baseline.The compressive sensing super-resolution algorithm is introduced into tomography SAR.The simulation results show that compressive sensing can not only solve the problem of low resolution caused by limited aperture size,but also solve the problem of de-focus caused by sparse baseline.The current FFBP algorithm is improved to better adapt to mobile trajectory.Combined with the compressive sensing in tomography direction,the tomography SAR can also obtain good 3D imaging effect when making maneuver ingestion trajectory flight,and simulation experiments verify the validity of the algorithm.The 3D imaging algorithm of high-squint curvilinear SAR is studied.The FFT-based curvilinear SAR 3D imaging algorithm is derived and simulated,and the effect of aperture shape on imaging effect is analyzed.The focus effect of several typical curve apertures is compared intuitively,which provides a basis for the selection of aperture shape.According to the sparseness of the observation scene,the adaptive 3D back-projection algorithm for high-squint imaging mode is proposed,which reduces the complexity of 3D projection imaging.The CLEAN algorithm is used to enhance the 3D image quality.The idea of aperture division is introduced into curvilinear SAR 3D imaging,and a fast 3D imaging algorithm based on virtual sub-aperture division is proposed.The long aperture is divided into short apertures and the full aperture image is obtained through sub-aperture image interpolation fusion.The calculation analysis shows that the complexity of the algorithm is significantly reduced,and simulation experiments verify the validity of the algorithm.