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The inverse synthetic aperture radar (ISAR) imaging of the target above the rough surface based on the time-domain (TD) electromagnetic (EM) scattering algorithms is focused on in this paper. It effectively combines TD ray tracing (TDRT) method for the composite scene and radar imaging model. The scattering echoes for ISAR imaging are solved by TDRT that the TD mutual coupling between the target and rough surface can be considered by the ray bounce strategy. Compared with the frequency domain ray tracing (FDRT) and multilevel fast multi-pole method (MFMM), TDRT algorithm not only ensures the calculation accuracy, but also greatly reduces the calculation cost. Then, we generate the ISAR image of the target above the rough surface according to the echo matrix based on TDRT. In order to improve the imaging quality of the target, the non-linear mapping theory is presented to suppress the virtual image points and noisy points and it is beneficial to the future research of target recognition in the composite scene.

An inverse synthetic aperture radar (ISAR) imaging framework is proposed to process transient scattered echoes into ISAR images. First, the time-domain shooting and bouncing ray (TDSBR) method is developed to simulate the transient scattering echoes. Then, based on the electromagnetic scattering echo expressions, the ISAR imaging formula is derived. In order to improve the imaging efficiency, we use Gaussian modulation pulse to replace the traditional linear frequency modulation pulse and propose an improved matched filtering method. Finally, some ISAR images are presented to demonstrate the accuracy and efficiency of the proposed method. Besides, by comparing with time-domain physical optics(TDPO) method, we also analyze the effect of multiple scattering contribution calculated by TDSBR on the image emphatically.

In the past, most of the transient electromagnetic (EM) analyses focused on the scattering from the target. The transient scattering from rough surface was rarely studied, especially for the layered rough surface. When the target is above the rough surface, it needs to solve the composite transient scattering from the rough surface and the target above it. In this article, we mainly focus on the time-domain (TD) analysis for transient scattering from the target and layered rough surface based on time-domain ray tracing (TDRT) modeling. Applying geometrical optics (GO), the multiple bounces of the transient EM waves between layered rough surfaces and target are traced to obtain the incident field of the irradiated surfaces. Then considering the particularity of the layered rough surface, we modify TD Gordon integral and reduce the TD physical optics (TDPO) integral to closed-form expressions to improve the computing efficiency. To demonstrate the efficiency and accuracy of the proposed algorithm, the transient scattering simulations of the composite model involving target and layered rough surface are compared with frequency-domain ray tracing (FDRT) with inverse fast Fourier transform (IFFT), as well as the results obtained by the multilevel fast multipole algorithm (MLFMA) of FEKO in conjunction with IFFT (IFFT-MLFMA). The characteristics of transient scattering from the composite model are further studied to show the physical phenomenon of scattering mechanisms. Specifically, the transient scattering from the composite model for different parameters is simulated for sensitivity investigation of the transient scattering to the variations in the related parameters.

Time-domain physical optics (TDPO) contour integral representations are developed for backscattered near fields from a perfectly conducting surface illuminated by a dipole source. The proposed representations are derived from the TDPO surface integral representations by introducing two theorems: surface gradient and surface divergence theorems. The proposed representations are free from singularities for all the source/observer positions in which the dipole antenna is located. In addition, the time-domain physical theory of diffraction is introduced to modify the physical optical field considering the effect of the edge diffraction. Numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method.

A ray tracing method based on the geometrical optics and physical optics approximation is proposed for calculation of the scattering from rough metal surface with rough coating in terahertz regime. Geometrical optics is utilized to describe the wave propagation concerning the reflection and transmission, whereas physical optics is applied to obtain the scattering fields by equivalent currents on the surfaces. The method provides a reliable treatment of scattering from rough layers involving identical/different roughness. The scattering predictions of the rough layers are compared to the multilevel fast multipole algorithm (MLFMA) to demonstrate the efficiency and accuracy of the proposed method. Once validated, we use the method to carry out a sensitivity study of the bistatic radar scattering cross section to variations in layer parameters of interest in terahertz coating target detection, such as the roughness of the coating and metal surface, thickness of the coating layer.

An efficient time domain shooting and bouncing ray (TDSBR) method is proposed to analyze the transient near-field scattering from an electrically large complex object illuminated by a far-field antenna source. The time-domain far-field incident sources can be derived by a convolution of pulsed excitation with the inverse Fourier transform of frequency domain (FD) far-fields radiated from an antenna. In order to obtain accurate near-field scattering results, time domain physical optics (TDPO) near-field integral representations are proposed and reduced to closed-form expressions to improve computing efficiency by applying locally expanded Green function approximation. Different from the plane wave incident situation, in the case of antenna radiation, the incident fields of each individual facet in the ray path are represented by the radiation fields from the equivalent mirror antenna derived in this paper. Since the radiation fields naturally contains the time delay term, the complicated processing of the time delay problem can be avoided by solving the equivalent mirror antenna radiation fields. It is simpler and more accurate than the traditional time domain geometrical optics (TDGO) method. Numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method.

In this paper, the scattered near-fields from electrically large complex PEC objects illuminated by far-field antenna sources are calculated by shooting and bouncing ray (SBR) method. In order obtain accurate near-field scattering results, an physical-optics (PO) near-field integral representation is proposed and reduced to closed form expressions to improve computing efficiency by applying locally expanded Green function approximations. By introducing the proposed PO near-field integral expressions, SBR can be used to analyze near-field scattering from a PEC target under far-field antenna sources radiation. The method is applicable to analyze the near-field scattering problem under arbitrary far-field source incident. Numerical example is presented to demonstrate the efficiency and accuracy of the proposed method.

An accurate and efficient physical-optics (PO) near-field integral representation is proposed to evaluate the near-fields scattering under dipole sources radiation. The coupling between targets and rough surface is analyzed by shooting and bouncing ray (SBR) method. By introducing the proposed PO near-field integral expressions, SBR can be used to analyze near-field composite scattering from a target above rough surface illuminated by dipole sources. Numerical examples are presented to demonstrate the exactness of the proposed method.