Research On Technologies Of Multibaseline SAR Three-Dimensional Imaging

Recently,synthetic aperture radar(SAR)three-dimensional(3-D)imaging technique has attracted wide attention due to its ability of achieving the distribution and scattering characteristics of targets in real 3-D space.Multibaseline SAR(MB SAR)is a 3-D SAR imaging mode with multiple flight tracks.It can be simply realized by using the existing SAR systems to form the sensing geometry with multiple passes.Therefore,MB SAR is a very promising 3-D SAR imaging mode.This thesis centre on the MB SAR imaging mode,and makes a deep investigation about the key technologies for the high-quality and high-resolution MB SAR 3-D imaging.The main contents and innovations can be summarised as follows:First,the fundamentals of the MB SAR 3-D imaging are investigated and analyzed.The fundamental imaging principles and spatial resolutions of two typical MB SAR imag-ing mode,i.e.,multibaseline linear SAR(MB LSAR)and multibaseline circular SAR(MB CSAR),are analyzed.Although the azimuthal motion tracks of the MB CSAR are differ-ent from that of the MB LSAR,these two modes have the same elevation imaging model.Therefore,the real data collected by the MB CSAR acquisition can also be used to verify the validity and feasibility of the proposed elevation processing methods in the thesis.Second,the problem of tomographic phase error calibration for the MB SAR 3-D imaging are investigated.Phase error calibration is a necessary step in the MB SAR 3-D imaging.The thesis first analyses the source and characteristic of the tomographic phase errors.Then,the method based on the phase gradient autofocus(PGA)and the method based on the sharpness optimization autofocus(SOA)are proposed to perform the phase error calibration in the MB SAR elevation imaging.Experimental results with real data verified the validity and feasibility of the proposed methods.Third,the problem of high-resolution elevation reconstruction for the MB SAR 3-D imaging is investigated.High-resolution elevation reconstruction is a key step in the MB SAR 3-D imaging.Usually,the length of total baseline in elevation is kept small to reduce the cost,which results in a coarse Rayleigh resolution in elevation.To real-ize super-resolution elevation reconstruction,a elevation reconstruction method based on the iterative adaptive approach(IAA)and generalized likelihood ratio test(GLRT)is proposed in this thesis.This method first performs elevation focusing using IAA and then makes a model order selection using GLRT to obtain sparse elevation reconstruc-tions.Compared with the widely used compressive sensing based methods,the proposed method does not need fine tuning of any hyperparameters,and can achieve almost the same super-resolution power and estimation accuracy with much higher efficiency.Fourth,3-D imaging using the multibaseline bistatic SAR(MB Bi SAR)is investi-gated.Bi SAR imaging mode has many advantages compared with the monostatic SAR imaging mode.By analysing the mathematical model of MB Bi SAR 3-D imaging,it is known that the elevation imaging model of the MB Bi SAR is the same as that of the mono-static MB SAR.In order to obtain high-quality Bi SAR 2-D images with high efficiency,a bistatic fast back projection(BP)algorithm based on the elliptical polar coordinate is proposed.Compared with the bistatic original BP algorithm,the proposed method can achieve almost the same 2-D image quality with much higher computational efficiency.After obtaining the Bi SAR 2-D images,the phase error calibration and reconstruction in elevation for the MB Bi SAR is the same with that for the monostatic MB SAR,and the corresponding methods for the monostatic MB SAR can be used for the MB Bi SAR el-evation processing.Therefore,the MB Bi SAR 3-D imaging can be seen as an extension of the traditional monostatic MB SAR imaging mode.The thesis has used MB SAR real data or simulated data to verify the proposed method,and the experimental results proved the correctness of the theoretical analysis and the validity and feasibility of the proposed method.Therefore,the research in the thesis is valuable both in theory and engineering.