The composite electromagnetic (EM) scattering characteristics of low-altitude target above valley composite rough surface are studied. The composite rough surface modeling theory is adopted to simulate the natural cavity structure of valley environment. Aiming at efficiently and accurately calculate the composite EM scattering from low-altitude target above valley environment, a hybrid method combining shooting and bouncing ray (SBR) technique and equivalent edge currents (EEC) method is proposed, in which SBR method based on the ray-density normalization (RDN) is applied to consider the multiple interactions between target and environment, and EEC method meliorates target's edge diffraction. Numerical examples illustrate the efficiency and validation of proposed hybrid method. Finally, based on the hybrid SBR-EEC method, the EM scattering characteristics of low-altitude target above valley environment are further investigated to show scattering mechanisms of this composite model and provide some useful conclusions through physical phenomena.

This paper proposes a hybrid method for computing electromagnetic scattering from target above composite rough surface of ground and near sea in adjacent region. First, a kind of composite rough surface for simulating ground and near sea in adjacent region is modeled by utilizing the Monte Carlo method, in which the ground region is modeled by adopting Gauss spectral function; the near sea region is modeled by adopting JONSWAP spectral function combined with shallow coefficient; diverse weighted inverse tangent functions are introduced to structure different boundaries and connect regions. Second, aiming at fast and accurately computing composite scattering from target above this kind of composite rough surface, a hybrid method with several acceleration strategies is proposed by combining adaptive iterative physical optics (AIPO) with method of equivalent currents (MEC), in which MEC meliorates edge diffraction. Finally, some examples verify the validation of the proposed hybrid method showing that: this hybrid method is an effective tool for analyzing the composite scattering characteristics of target above practical environment during radar detection and SAR imaging, and we also give the composite scattering from target above composite rough surface with different incident angle, shape of boundary and statistic parameters. Moreover, composite scattering from different targets above this kind of composite rough surface model is studied in order to provide some useful conclusions.

This article proposes a hybrid iterative solver for modeling composite rough surface electromagnetic scattering. First, a kind of divisional rough surface with the shape of a round water zone embedded in a larger land rough surface is modeled, in which the former is built by Pierson-Moscowitz spectrum; the latter is by Gauss spectrum. Second, aiming at fast computing scattering from this kind of composite rough surface with large scale and fast waving, a hybrid iterative solver is based on forward-backward iterative physical optics with several acceleration strategies, as well as impedance boundary condition. Finally, numerical results show that this hybrid iterative solver can satisfy the requirement for high efficiency, reliable precision in computing scattering from large scale composite rough surface.

The electromagnetic (EM) scattering characteristics of target above coastal environment are complicated due to the simultaneous existence of ground region and sea region. Nevertheless, the actual target possesses both conducting part and dielectric part. Such a composite scattering problem involves multiple media parameters and large amount of unknowns. Hence, aiming at accurately and efficiently calculating the EM scattering from combined conducting and dielectric target above coastal environment, the hybrid SIE-KA method is introduced in which single integral equation (SIE) method is utilized to reduce the number of combined target’s unknowns and Kirchhoff approximation (KA) is applied to obtain induced electric and magnetic current on the surface of coastal environment. Moreover, multilevel fast multipole algorithm (MLFMA) is adopted to significantly reduce the computational cost and memory requirement. Several numerical examples demonstrate the accuracy and efficiency of the hybrid method. Finally, the EM scattering characteristics of combined conducting and dielectric target above coastal environment have been studied. The radar cross section (RCS) curves with different category of environment, polarization mode, working frequency, statistic parameters of coastal environment, permittivity of target’s dielectric part, target’s height and target category have been analyzed in detail to provide some useful conclusions. The approach and results can be broadly applied in remote sensing simulation of coastal environment with combined target.

Due to simplicity, hybridization of shooting and bouncing ray (SBR) and physical optics (PO) has been widely used for fast scattering analyses. A composite random rough surface model is presented for describing the concave structure of strait environment. Monte Carlo method is used to build strait composite random rough surface, gauss spectral function is used to simulate ground part of strait, and Pierson Moskowitz (PM) spectral function is used to simulate ocean part of strait. Weighted inverse tangent function is presented to smooth adjacent region. The ray-density normalization (RDN) theory is introduced to improve the SBR method. In consideration of the inartificial cavity construction of strait in natural environment, the improved SBR/PO is used to calculate the electromagnetic scattering of the strait composite rough surface. Electromagnetic scattering characteristics of ground, ocean, and strait composite random rough surface are compared. The impacts of open area of strait concave structure on the curves of bistatic scattering coefficient (BSC) of horizontal-to-horizontal (HH) polarization of strait environment are analyzed. The influence of root mean square (RMS) of ground region on BSC of HH polarization is discussed. The numerical results can use for reference in the fields of remote sensing, detection and inversion of electromagnetic environment.

In this paper, an improved hybrid scheme combining the method of moment (MoM) and physical optic (PO) is proposed to analyze composite scattering from multiple 3D conductingobjects above a 2D random rough dielectric surface. In the calculation scheme, rough surface scattering is calculated using the PO method and target scattering is calculated by the MoM. The coupling interactions between the multiple targets are considered using the domain distribution method (DDM), where the matrix equations are constructed upon each individual target and are then presented and solved as a whole. The contribution from rough surface scattering, which is calculated by the PO method, is coupled with the impedance matrix, and the unknowns must be considered only in the MoM region. Most of the composite scattering problems are computing interactions between objects and rough surface, and solving the complex impedance matrix equation in the MoM part. To solve these two problems, first, the combined multilevel fast multipole algorithm (MLFMA) and the fast far field approximation (FaFFA) are introduced to accelerate interactions between objects and rough surface, where the near area on the rough surface is computed by MLFMA, while the far area is computed by FaFFA. In addition, to further improve the efficiency, the adaptive integral method (AIM) is employed to solve the impedance matrix equation of the MoM part in the scheme. The results are compared to those obtained with the traditional MoM-PO method, showing that the hybrid method proposed in this paper can maintain a high accuracy with a much smaller computational time and fewer resource requirements. The numerical results obtained under several different conditions are presented and discussed in this paper.