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This research involved studying the characteristics of composite electromagnetic scattering from a rocket moving above actual terrain using the finite-difference time-domain method. The angular distribution curve of the composite scattering coefficient was obtained, and the influences of factors such as the angle of incidence, the frequency of the incident electromagnetic wave, the content of moisture in soil, the dielectric constant of the rocket-shell material, the height of the rocket, and the undulation of the terrain on the composite scattering coefficient were investigated. Results show that the composite scattering coefficient oscillates with the scattering angle and increases in the direction of mirror reflection. It also decreases with increasing angle of incidence, frequency of the incident wave, and altitude of the rocket, while it increases with increasing soil moisture and dielectric constant of the rocket-shell materials. Although the influence of different terrain undulations on the composite scattering coefficient is noticeable, it follows no fixed pattern. [ABSTRACT FROM AUTHOR]

In this study, we obtained the intensity and orbital angular momentum (OAM) spectral distribution of the scattering fields of vortex electromagnetic beams illuminating electrically large targets composed of different materials. We used the angular spectral decomposition method to decompose a vortex beam into plane waves in the spectral domain at different elevations and azimuths. We combined this method with the physical optics algorithm to calculate the scattering field distribution. The OAM spectra of the scattering field along different observation radii were analyzed using the spiral spectrum expansion method. The numerical results indicate that for beams with different parameters (such as polarization, topological charge, half-cone angle, and frequency) and targets with different characteristics (such as composition), the scattering field intensity distribution and OAM spectral characteristics varied considerably. When the beam parameters change, the results of scattering from different materials show similar changing trends. Compared with beams scattered by uncoated metal and dielectric targets, the scattering field of the coating target can better maintain the shape and OAM mode of beams from the incident field. The scattering characteristics of metal targets were the most sensitive to beam-parameter changes. The relationship between the beam parameters, target parameters, the scattering field intensity, and the OAM spectra of the scattering field was constructed, confirming that the spiral spectrum of the scattering field carries the target information. These findings can be used in remote sensing engineering to supplement existing radar imaging, laying the foundation for further identification of beam or target parameters. [ABSTRACT FROM AUTHOR]

The rough structure may affect the flow field and electromagnetic (EM) scattering characteristics of a hypersonic vehicle. In this study, the EM scattering characteristics of the hypersonic vehicle RAM C-II with a microrough surface were investigated in the millimeter wave band. We first simulated the flow field of a smooth RAM C-II vehicle and calculated the radar cross section (RCS) in the wideband using the physical optics method. The calculation results show that many factors contribute to the variation in the RCS; however, it is occasionally difficult to predict. We then used a one-dimensional Gaussian random rough surface to generate a RAM C-II with a microrough surface through a point-coordinate transformation and simulated its flow field. The electron density flow field of the rough surfaced aircraft fluctuates greatly on the wall. Finally, we calculated the RCS of RAM C-II with different values of roughness in the millimeter wave band. The change of surface structure can be reflected in millimeter waves, and the RCS is determined by both plasma and rough structure. [ABSTRACT FROM AUTHOR]

Electromagnetic (EM) scattering of sea surface may exhibit sea-spikespikes when there exist breaking waves. As sea-spikes are usually mistaken for targets, the investigation of EM scattering characteristics and high-range resolution profiles (HRRPs) of three-dimensional (3D) sea surfaces with a plunging breaker is meaningful for target detection and recognition. To describe the basic features of a plunging breaker, this paper developed a feasible and wind-related plunging breaker model. Here, profiles of a plunging breaker in its life cycle are modeled according to the wind speed and time factor, and the small-scale roughness is considered. Then, the sea surface and plunging breaker are combined to obtain the composite model. Additionally, a hybrid algorithm based on the Capillary Wave Modification Facet Scattering Model (CWMFSM) and ray tracing technique is developed to calculate the EM scattering of 3D sea surface with a plunging breaker. Simulation results show that the sea-spike phenomenon is more likely to occur for the upwind and large incident angles. The amplitude of the backscattering electric field from the plunging breaker is much stronger than that of the sea surface. Furthermore, the HRRPs of 3D sea surface with a plunging breaker and target are computed. Sharp peaks from the plunging breaker that exhibit obvious target-like features are observed. [ABSTRACT FROM AUTHOR]

An Improved Particle Swarm Optimization Algorithm-Support Vector Regression Machine (IPSO-SVR) prediction model is developed in this paper to predict the electromagnetic (EM) scattering coefficients of the three-dimensional (3D) sea surface for large scenes in real-time. At first, the EM scattering model of the 3D sea surface is established based on the Semi-Deterministic Facet Scattering Model (SDFSM), and the validity of SDFSM is verified by comparing with the measured data. Using the SDFSM, the data set of backscattering coefficients from 3D sea surface is generated for different polarizations as the training samples. Secondly, an improved particle swarm optimization algorithm is proposed by combining the Particle Swarm Optimization (PSO) and Genetic Algorithm (GA). The combined algorithm is utilized to optimize the parameters and train the SVR to build a regression prediction model. In the end, the extrapolated prediction for backscattering coefficients of the 3D sea surface is performed. The Root Mean Square Error (RMSE) of the IPSO-SVR-based prediction model is less than 1.2 dB, and the correlation coefficients are higher than 91%. And the prediction accuracy of the PSO-SVR-based, GA-SVR-based and IPSO-SVR-based prediction models is compared. The average RMSE of the PSO-SVR-based and GA-SVR-based prediction models is 1.4241 dB and 1.6289 dB, respectively. While the average RMSE of the IPSO-SVR-based prediction model is reduced to 1.1006 dB. Besides, the average correlation coefficient of the PSO-SVR-based and GA-SVR-based prediction models is 94.36% and 93.93%, respectively. While the average correlation coefficient of the IPSO-SVR-based prediction model reached 95.12%. It demonstrated that the IPSO-SVR-based prediction model can effectively improve the prediction accuracy compared with the PSO-SVR-based and GA-SVR-based prediction models. Moreover, the simulation time of IPSO-SVR-based prediction model is significantly decreased compared with the SDFSM, and the speedup ratio is greater than 15.0. Therefore, the prediction model in this paper has practical application in the real-time computation of sea surface scattering coefficients in large scenes. [ABSTRACT FROM AUTHOR]

The face-centered cube (FCC) grid has more sampling points than the traditional Yee cell (as it contains a total of 14 grid points, of which six are center points and eight are vertices, and each grid point has three field components). Thus, FCC is better than the former in dealing with the dispersion error of anisotropic media. On the basis of this feature, this article first derived the FCC-finite-difference time-domain (FDTD) iterative formula for nonuniform plasma on the basis of FCC grid and verifies the accuracy of the algorithm. This algorithm is combined with the nonuniform plasma flow field model of hypersonic vehicles, and the backward single-station radar cross sections (RCSs) of vertical polarization (VV) and horizontal polarization (HH) are calculated under different flight altitudes, flight velocities, and external conditions. Results showed that as flying height increased or flying speed decreased, it results in an increase in RCS. Different external magnetic fields and incident angles also had an obvious impact on the electromagnetic scattering characteristics. From the perspective of electromagnetic wave polarization, both VV polarization and HH polarization have a great impact on RCS. These results provide a theoretical basis for studying the electromagnetic scattering characteristics of nonuniform plasma targets. [ABSTRACT FROM AUTHOR]

A new electromagnetic (EM) scattering model of the sea surface with single breaking waves is proposed based on the high-frequency method in this paper. At first, realistic breaking wave sequences are obtained by solving the fluid equations which are simplified. Then, the rough sea surface is established using the linear filtering method. A new wave model is obtained by combining breaking waves with rough sea surface using a 3D coordinate transformation. Finally, the EM scattering features of the sea surface with breaking waves are studied by using shooting and bouncing rays and the physical theory of diffraction (SBR-PTD). It is found that the structure that is similar to a dihedral corner reflector between the breaking wave and rough sea surface exhibits multiple scattering, which leads to the sea-spike phenomenon that the scattering result of horizontal (HH) polarization is larger than that of vertical (VV) polarization, especially at low-grazing-angle (LGA) incidents with upwind. The sea-spike phenomenon is also closely related to the location of strong scattering. [ABSTRACT FROM AUTHOR]

A new electromagnetic (EM) calculation model, the inhomogeneity zonal medium model (IZMM) (based on the physical optics (PO) method), is proposed to calculate and analyze the EM scattering characteristics of hypersonic vehicle covered with a plasma sheath. First, the flow field of the plasma sheath is divided into nonuniform calculation subregions with different spacing sizes. The shape of the external flow field of the aircraft is modeled by fitting with a paraboloid and circular platform with different radii. Then, the electron density, temperature, and pressure distribution are obtained by collecting data from different points in the flow field of the sheath. Finally, a piecewise PO method is used to calculate the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath from $L$ -band to $X$ -band. The numerical results show that the EM scattering characteristics of a target spacecraft covered with a plasma sheath can be described more accurately by using zoned medium model simulation. Under different flying conditions, the BRCS of hypersonic vehicle covered with a plasma sheath appears to be reduced to different degrees in the $S$ -band and the band range of 7–11 GHz, and a large attenuation of BRCS occurs in the head area of the aircraft. The research results enrich the EM modeling method of hypersonic vehicles, overcome some shortcomings of the existing PO method, and provide technical support and innovative ideas for the accurate analysis of the EM scattering characteristics of hypersonic targets. [ABSTRACT FROM AUTHOR]

To investigate the electromagnetic scattering problem related to a foil in a turbulent hypersonic plasma environment, the scattering field formulas for hypersonic plasma turbulence were improved by applying the anisotropic power spectrum. Using the theory of electromagnetic scattering of a conducting object, the second moment of a conducting object's scattering field is obtained in the hypersonic plasma turbulence. Finally, the backscattering cross-section of the foil surrounded by the hypersonic plasma turbulence was calculated. The results showed that the fractal dimension led to an increase in the complexity of the hypersonic turbulent structure, and thus had a greater influence on the electromagnetic wave scattering. The scattering cross-section of the foil in the hypersonic turbulence decreases rapidly. Meanwhile, the anisotropic parameters in the model represent scale-dependent stretching of the turbulent eddy. As the anisotropic parameters of the turbulence increase, there will be less scattering of the hypersonic turbulence. At this point, the total scattering cross-section of the foil in hypersonic plasma turbulence increases gradually. By improving the aerodynamic shape of the aircraft, it can produce a large number of anisotropic turbulent eddies which can effectively improve the passive jamming capability when the foil is cast. [ABSTRACT FROM AUTHOR]

An efficient approach to analyze the electromagnetic (EM) scattering from coated objects above a three-dimensional (3-D) dielectric random rough surface is proposed in this paper. The electric and magnetic current densities on the sea surface are analytically realized using the semi-deterministic facet scattering model (SDFSM). Considering Fresnel reflection coefficient, a scheme combining the shooting and bouncing rays (SBR) and the physical theory of diffraction (PTD) is developed to calculate the scattering of the coated objects. Simulation results obtained with the combined method are verified by comparison with exact simulations using the multilevel fast multiple method (MLFMM). Scattering of large coated objects over sea surface composite model are too large and complex to be calculated using exact methods. With the asymptotic approach in this paper, the scattering performance can be analyzed with rather moderate computational efforts. Numerical results of composite scattering from an electric large three-dimensional model, e.g. an airplane target over a randomly rough surface with Pierson Moskowitz (PM) spectrum are presented and discussed. [ABSTRACT FROM AUTHOR]

3-D time-varying and spatially nonuniform plasma is applied using the finite-difference time-domain algorithm in investigating the effects of electromagnetic (EM) wave scattering in the plasma sheath. The plasma sheath is stratified in space, and three types of electron density in time-varying forms are assumed. The characteristics of different time-varying forms are analyzed using radar cross section (RCS). In addition, the effects of RCS change with time at S - and L -bands are investigated using electron density as the time variable. In the condition of time-varying and spatially nonuniform plasma sheath, the attenuation of EM wave is affected by different time-varying regularities of electron density ( ne ). The RCS varying with time is related to the change rate of ne . [ABSTRACT FROM PUBLISHER]

This paper is aimed at applying the multiregion model to the composite EM scattering from a dielectric target and a dielectric rough surface. In the multiregion model, the rough surface is divided into multiple regions, the method of moment (MoM) is only adopted in the dominant region. Hence, this model can markedly reduce the number of unknowns. Firstly, we derived the single integral equation (SIE) in which the number of unknowns is half of those in the conventional MoM and the equations will be easier to deal with. Then the multiregion model is extended by SIE. With the multiregion model, one can obtain the accurate equivalent currents on the dominant region and accurate bistatic scattering coefficient in small and moderate scattering angles with much less time and memory requirement. [ABSTRACT FROM AUTHOR]

We propose an inverse synthetic aperture radar (ISAR) imaging algorithm for a composite target-ocean scene based on time-domain shooting and bouncing rays (TDSBR) method. To do this, we develop the TDSBR method to simulate the electromagnetic scattering echoes from a composite target-ocean scene. Then, we derive the ISAR imaging formulas based on electromagnetic scattering field expressions. The demodulation, pulse compression, and azimuth inverse fast Fourier transform are performed on the scattering echo data to obtain ISAR images. Linear frequency modulation (LFM) pulses are usually used in traditional radar imaging. However, its long pulse width leads to more computation time for simulations. To increase efficiency, we replace LFM pulses with modulating Gaussian pulses. As a result, we modify the matched filter to achieve pulse compression under modulating Gaussian pulse excitations. Simulation results confirm that this proposed method improves efficiency while ensuring image quality. This proposed technique fully incorporates the electromagnetic scattering mechanism and is accurate. It effectively combines the electromagnetic scattering algorithm and the radar imaging algorithm. Finally, we present ISAR images simulated by this method. These results confirm the feasibility and efficiency of this technique. [ABSTRACT FROM AUTHOR]

Based on the detection platform of space-borne radar (SBR), the dynamic electromagnetic (EM) scattering characteristics of a hypersonic vehicle covered with plasma sheath are calculated and analyzed by the physical optics (PO) method. Using the angle-time conversion method, the dynamic radar cross section (DRCS) of the vehicle in horizontal flying path and different flying states is solved in the range of L-band to X-band. The relevant effective statistical features are extracted from the time-scale matrix of DRCS based on continuous wavelet transform (CWT). The numerical results show that: At different flying altitudes, the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath has irregular fluctuation and large range reduction in the head region of the vehicle. Generally, the higher the incident EM wave frequency is, the more detailed the fluctuation characteristics of the DRCS can be reflected. Within the same radar illuminate angle range, the time consumed by the vehicle DRCS is inversely proportional to the flying height and flying speed and is directly proportional to the detection altitude of the SBR. Besides, the different kinds of statistical eigenvalues extracted from DRCS will play an important role in hypersonic targets classification and recognition. [ABSTRACT FROM AUTHOR]