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This article presents the computation of the backscattered field in simulation of synthetic aperture radar (SAR) raw data. We develop an improved Kirchhoff approximation to estimate the surface fields induced by the incident waves. The improved Kirchhoff approximation is a second-order iterative solution of the integral equations governing the targets’ electric and magnetic current densities. In computing the second-order re-radiated fields, we applied the shoot-bouncing-ray (SBR) technique to enhance propagation path tracking efficiency. The geometrical theory of diffraction (GTD) was employed to account for the diffraction fields from the edges and wedges, which constitute the total scattered fields collected by SAR in synthetic aperture. As the SAR moves along the azimuth direction, the backscattered signal computation is repeated as the antenna beam crosses the targets. This procedure demands heavy computational resources but requires no priori assumptions of radar cross-sections (RCSs) nor speckle statistics. The raw data is generated as an output signal of the SAR system response into which the backscattered signal is input. We chose three types of the target to demonstrate our approach to confirm the effectiveness. The first set of targets are three dihedral reflectors – two of them were rotated to constitute three unique scattering matrices. The results show that the polarimetric information, both relative amplitudes and phases, are well–preserved. The second target is a rough surface with exponential power spectral density and Gaussian height probability density. We examined image speckle statistics of multi-looking image. The third target type is an electrically large cargo ship (container) sitting over a sea surface. Polarimetric analysis via the Pauli and Y4R decompositions reveals that the polarimetric features are well preserved. Simulation results demonstrate that the present approach is fully coherent in streamlining the data flow from backscattered field to complex single look images within the SAR imaging scene. [ABSTRACT FROM AUTHOR]

Passive millimeter-wave and terahertz (MMW/THz) imaging is a significant technique used in personal security inspection and scene surveillance. However, a human body generally generates an obvious reflection on the floor, which may have negative influences on target detection and observer vision. In this article, we present a physically based method using dual-polarization feature and saliency information to solve the problem of reflection removal. The physical principle of a special dual-polarization phenomenon has been revealed by theoretical calculation and simulation analysis. By combining the second Stokes parameter (TQ) and modified linear polarization ratio (mLPR), a new feature parameter has been created to extract reflections of human bodies. By using a saliency analysis, the false positive alarms are eliminated completely. The experimental results demonstrate the robustness and effectiveness of the proposed method using various measured MMW/THz images. [ABSTRACT FROM AUTHOR]

Passive millimeter-wave (PMMW) imaging has been used for several close-range applications such as personal security checks, scene monitoring, and so on. PMMW images contain a variety of types of image edges which represent intensity discontinuities. As a special edge, an object contour edge is an important feature for object detection and recognition, which denotes the external shape of the object. In this article, a physically based contour edge display method using adjustable linear polarization ratio (ALPR) by multipolarization imaging is proposed. Polarization brightness temperature (TB) models of the object and radiometer observation are built. According to the physical principle of edge generation, the ALPR properties of the contour edge are investigated. By fusing multipolarization information, the simple feature parameter ALPR is sensitive to the object contour edge. Then, the specific operation process of the proposed method based on multipolarization images is presented. Simulations and measurements of polarimetric imaging for personal security inspection scenes were conducted to verify the contour edge display performance. Finally, the applicability of the method is discussed and summarized. [ABSTRACT FROM AUTHOR]

In this paper, a 3-D diffraction tomographic algorithm is proposed for real-time through-the-wall radar imaging (TWRI). The spectral expansion of the three-layered medium dyadic Green's function is employed to derive a linear relationship between the spatial Fourier transforms of the image and the scattered field under Born approximation. Then, the image can be efficiently reconstructed with inverse fast Fourier transform (IFFT). The linearization of the inversion scheme and the easy implementation of the algorithm with FFT/IFFT make the diffraction tomographic TWRI algorithm suitable for on-site applications. The 3-D polarimetric TWRI is investigated using the proposed algorithm for the enhanced target detection and feature extraction as well as mitigation of the wall effect in the cross-polarization. Numerical and experimental results are presented to show the effectiveness and high efficiency of the proposed algorithm for 3-D real-time TWRI. [ABSTRACT FROM AUTHOR]

We consider the problem of through-the-wall radar imaging (TWRI), in which polarimetric imaging is used for automatic target detection. Two generalized statistical detectors are proposed which perform joint detection and fusion of a set of multipolarization radar images. The first detector is an extension of a previously proposed iterative target detector for multiview TWRI. This extension allows the detector to automatically adapt to statistics that may vary, depending on target locations and electromagnetic-wave polarizations. The second detector is based on Bayes' test and is of interest when target pixel occupancies are known from, e.g., secondary data. Properties of the proposed detectors are delineated and demonstrated by real data measurements using wideband sum-and-delay beamforming, acquired in a semicontrolled lab environment. We examine the performance of the proposed detectors when imaging both metal objects and humans. [ABSTRACT FROM AUTHOR]