Investigations In To Advanced Techniques For High-resolution Signal Processing Of Downward-looking Imaging Radar

Synthetic aperture radar(SAR)is widely used in both civil and military applications due to its remarkable high resolution and all-weather imaging capability.Conventional SAR operates in a side-looking or oblique mode,which inevitably poses problems of shadowing and cascading.Linear Array Synthetic Aperture Radar(LASAR)overcomes the problems caused by the traditional SAR working mode by erecting a linear array in the vertical course direction to achieve a change of working mode-downward-looking imaging.At the same time,it relies on the linear array to obtain the resolution capability in the vertical course direction,thus realizing three-dimensional imaging.However,due to the limited size of the linear array,there will be a problem of insufficient resolution in the vertical line direction.For this reason,this paper proposes a forward downscale imaging radar system based on LASAR-simulating the linear array as a virtual beam for range scanning,and using super-resolution technology to obtain high resolution beyond the radar beam width through signal processing methods,so as to obtain more complete and accurate information about the scene.In this paper,based on the system architecture and technical regime of forward and downward looking imaging radar,we focus on echo modeling and super-resolution imaging algorithms,and the main work includes:1、 Overview of the research background and research significance of this topic.The development process of radar imaging is introduced,several current 3D imaging radar systems are described,with emphasis on LASAR,and the research status of super-resolution imaging technology and its application in scanning radar are reviewed.Finally,the main work content and structural arrangement of this thesis research are introduced.2 、 For the spatial geometric structure of the forward downsight imaging radar,the historical distance between the imaging target and the carrier platform is analyzed;the establishment of the radar echo model is completed;the preprocessing method is used to construct the echo convolution model in the vertical course direction;the pathological mechanism in it is analyzed;the relationship between the theoretical limit of the super-resolution algorithm and the relevant parameters is deduced.3、For the problem of insufficient resolution in the vertical airline direction,the positive downside TV-BR super-resolution algorithm is proposed based on the TV algorithm.Firstly,the classical super-resolution methods-the algorithm of maximum likelihood estimation based on prior information and the algorithm of maximum a posteriori estimation-are analyzed;according to the characteristics of the echo model of positive downsight imaging,different gradient operators are introduced jointly as the constraints of the objective function,and the L-curve method is used to interleave the fixed regularization parameters to constrain the operators,and finally,the r-split Bregman method is used in the framework of MAP solving.Through simulation,it is verified that the algorithm can effectively improve the detection capability of radar for scene details and terrain contours.4.The conventional two-dimensional SAR algorithm is studied and analyzed,and pushed to three dimensions;based on the application scene characteristics and echo model characteristics of positive downside 3D imaging,the Pdhr-SAR algorithm for positive downside 3D high-resolution imaging based on super-resolution-SAR joint processing is proposed,and the effectiveness of the algorithm is verified by simulation.