Targets In Random Media Research Articles

Experimental Demonstration of Statistical Stability in Ultrawideband Time-Reversal Imaging

We experimentally verify the statistical stability of ultrawideband time-reversal-based imaging of targets in discrete random media using electromagnetic waves. The measurements are carried out using a time-domain radar system that provides useful bandwidth of up to 40 GHz. We study the effect of the excitation bandwidth, discrete scatterers permittivity and fractional volume, and radar aperture size on the image stability. We also address the problem of imaging nonstationary targets in random media, where we verify the statistical stability of a differential time-reversal technique suited for tracking.

Influence of Incident Waves on Resonance in Backscattering from Targets in Random Media

The main concern of this study is the effect of incident wave properties on the resonance that occurs when the target size is close to the wavelength. In doing that, the laser radar cross-section of a conducting target is calculated using a boundary value method with a beam wave incidence and H-wave polarization. Therefore, the effect of creeping waves, produced with H-wave incidence, on the backscattering enhancement would be clarified. A comparison with a similar scattering problem using a plane wave incidence is considered.

Effect of H-wave polarization on laser radar detection of partially convex targets in random media

A study on the performance of laser radar cross section (LRCS) of conducting targets with large sizes is investigated numerically in free space and random media. The LRCS is calculated using a boundary value method with beam wave incidence and H-wave polarization. Considered are those elements that contribute to the LRCS problem including random medium strength, target configuration, and beam width. The effect of the creeping waves, stimulated by H-polarization, on the LRCS behavior is manifested. Targets taking large sizes of up to five wavelengths are sufficiently larger than the beam width and are sufficient for considering fairly complex targets. Scatterers are assumed to have analytical partially convex contours with inflection points.

Backscattering from conducting targets in continuous random media for circular polarization

The polarization of incident waves is one of the key factors in radar detection and remote sensing problems. In a previous study, attention was drawn to the anomalous increase in the radar cross-section (RCS) of a target in a random medium that occurs with H-polarization. This large increase occurs with a small-size target and is attributed to the coupling between the direct and creeping waves. In this work, we aim to probe the effect of the creeping waves on the scattering waves for circular wave polarization and compare it with the previous results. Therefore, we can control the target detection by choosing the proper polarization, which does not lead to anomalous phenomena. In doing so, we present numerical results for RCS and analyse the characteristics of the enhancement in the RCS (ERCS) behaviour of targets in random media. In this regard, we assume partially convex targets of different configurations. We consider the case in which a directly incident wave is produced by a line source distributed uniformly along the axis parallel to the conducting cylinder (target) axis. Then we can deal with this scattering problem two-dimensionally under the condition of strong continuous random media with large local scale size.

Numerical Analysis of Some Scattering Problems in Continuous Random Medium

Abstract—In this paper, we present numerical analysis for the following scattering problems: the radar cross-section, the backscattering enhancement, and the angular correlation function for waves scattered from practical targets embedded in random media. We assume perfect conducting targets with various cross-sections to study the effect of target configuration on the scattering problems. Also, we consider different random media with taking account of incident wave polarization. The scattering waves from conducting targets in random media can be estimated by a numerical method that solves the scattering problem as a boundary value problem. In this method, we use current generator and Green’s function to obtain an expression for the scattering waves.

An indirect estimate of RCS of conducting target in random medium

This paper discusses an indirect estimate of the radar cross section (RCS) of a conducting cylinder with a partially convex cross-section under the condition that backscattering enhancement occurs in a random medium. Once we evaluate the spatial coherence length (SCL) of the incident waves around the cylinder in the random medium, we may estimate the RCS approximately from the RCS in free space with beam wave incidence in which the spot size equals the SCL. This method is restricted only to the case where the SCL is larger than the target size.

NUMERICAL ANALYSIS OF SOME SCATTERING PROBLEMS IN CONTINUOUS RANDOM MEDIUM - ABSTRACT

In this paper, we present numerical analysis for the following scattering problems: the radar cross-section, the backscattering enhancement, and the angular correlation function for waves scattered from practical targets embedded in random media. We assume perfect conducting targets with various cross-sections to study the effect of target configuration on the scattering problems. Also, we consider different random media with taking account of incident wave polarization. The scattering waves from conducting targets in random media can be estimated by a numerical method that solves the scattering problem as a boundary value problem. In this method, we use current generator and Green's function to obtain an expression for the scattering waves.

Strong backscattering enhancement for partially convex targets in random media

Earlier work pointed out that the radar cross section (RCS), owing to the double-passage effect on waves propagating through random media, is enhanced by a factor ranging from one up to three. However, our study has manifested numerically a strong enhancement in RCS of targets with concave-convex surfaces in continuous random media, by taking account of boundary conditions of waves on targets. We have found that when a plane wave illuminates a convex portion of the concave–convex conducting target in a random medium, the factor of enhancement oscillates about two with target size. Moreover, this enhancement becomes quite large at certain target shapes and also under a specific condition of target size and spatial coherence length of the incident H-wave. The large enhancement is considered as an anomalous feature in the behaviour of backscattered waves in random media. By analysing the scattering problem for beam-wave incidence on the same target in free space, we manifest the mechanism of such anomalous enhancement.