Fundamental Study on Sensing of Targets in Random Media

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A method is presented for analyzing wave scattering of a conducting target in a random medium as a boundary value problem. The problem of the wave scattering can generally be formulated by introducing two operators : a Green's function in a random medium and a current generator, a new idea, which transforms any incident wave into a surface current on the target. The current generator depends on the target only and is mathematically constructed by Yasuura's method. The rader cross-section (RCS) of the target is expressed in terms of the current generator and the moment of the Green's function. The moment is approximately given as a solution of the moment equation in a random medium.The RCS of a conducting circular cylinder and elliptic cylinder in a strong turbulent medium where an incident wave becomes incoherent on the cylinder are numerically analyzed by a high-speed computer, and the characteristics of RCS are made clear for a conducting convex cylinder. As compared with the RCS of … More the cylinder in free space (sigma_0), the RCS in the turbulent medium (sigma_0) changes largely as a function of the spatial coherence length of the incident wave (L), the length of the axis transverse to the direction of incidence (d), the curvature of the cylinder surface directly illuminated by the incident wave, and the polarization of the incident wave : E-and H-waves. The change of sigma is summarized as follows : (1) For L*d, we have sigma*2sigma_0. (2) For L*d, sigma*2sigma_0 for E-wave incidence ; and the sigma for H-wave incidence changes largely, depending on the curvature of the cylinder, because of the creeping current on the cross-section surface. (3) For L<d, when the curvature changes rapidly, we have sigma_0<sigma*2sigma_0 for E-wave incidence and sigma*3sigma_0 in a case for H-wave incidence. When the curvature becomes flat, we have sigma*sigma_0 in some cases and sigma<sigma_0 in a case, for E-wave incidence, and sigma*0.5sigma_0 in a case for H-wave incidence. For L<d, we need to estimate the sigma in any cases carefully by our method. Less