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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.

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.