Research On The Imaging And Correction Method Of Unknown Wall Parameters By Through-wall Radar

Since the 1990 s,through wall radar technology has gradually become a hot research direction of scholars at home and abroad.Because it can “see” the target through the obstacles,that is,it can image the scene through the wall so as to determine the specific position of the target object.Because of its high resolution and strong penetrability,it is widely used in various fields.When imaging through wall scene,electromagnetic wave will be reflected and refracted many times when it meets the wall in the process of propagation,and its amplitude and phase will be attenuated and distorted.In addition,due to the influence of the material of the wall,its relative dielectric constant is greater than that of the air.Therefore,the propagation speed of the electromagnetic wave in the wall is slower than that in the air,which leads to the increase of its propagation delay,and then affects the presentation of the target position in the imaging.Moreover,in practical application,the wall parameters are unknown,and the wall is generally not composed of a single layer of uniform media,which brings greater challenges to imaging work.In view of the above problems,this paper makes the following related research:(1)In the case of known wall parameters,the compensation method of through wall radar imaging based on refraction theorem calculates the refraction point coordinates of electromagnetic wave inside the wall,thus confirming its propagation path and calculating the propagation delay of electromagnetic wave inside the wall.The BP imaging algorithm can restore the target to the correct position.However,under the condition of unknown wall parameters,it is impossible to accurately calculate the refraction point coordinate of electromagnetic wave,using the auto-focus method to determine the value range of electromagnetic wave propagation delay,all imaging results in the range of values are evaluated by image evaluation criteria,and selecting image quality evaluation function reaches the maximum value of radar image as the final result of imaging.In addition,aiming at the problem of too many iterations and too much computation,an improved auto-focus algorithm is proposed,which improves the computational efficiency and saves the computational time.(2)When the wall is double-layer and the parameters are unknown,a new algorithm of synthetic delay time of through wall radar imaging based on refraction static correction is proposed in this paper.Firstly,the overdetermined equations are established by reading the echo information to calculate the propagation delay of electromagnetic wave in outer wall.Then the propagation delay of each channel in the inner wall is estimated by the composite delay time increment.Finally,the abnormal propagation delay of each channel is corrected one by one,so that the imaging target is corrected to the accurate position.The effectiveness of the algorithm is verified by simulation and data analysis.(3)Using the Lab VIEW software to develop a test software for synthetic delay time method of through-wall radar imaging.Adding input controls on the interface can input different wall parameters and the gaussian noise of different intensity to test the performance of the algorithm.The MATLAB Script node provided by Lab VIEW is used to realize the mixed programming of Lab VIEW and MATLAB,and the program block diagram of the test software is built in the back panel.Finally,the intensity map and waveform map are output to observe the radar imaging results and the profile curve of the target location.