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Communication Dans Un Congrès Année : 2017

Propagation and scattering in a ducting maritime environment from a fast method of moments

Résumé

In coastal and maritime regions the microwave propagation is affected by the high variability of the meteorological parameters in space and time. This variability leads to respective changes in the tropospheric refractive index, namely ducting effect, which implies that the Radar wave is trapped near the surface and can propagate over a long distance. The ducting is present for a small percent of time but it significantly influences the radar and communications systems working in the microwave range. Then, the presence of a duct strongly affects the propagation, but also jointly, the scattering from the sea surface. For a longtime, The Parabolic Wave Equation (PWE) method combined with SSF (Split- Step Fourier), has been widely used to model radiowave propagation in a cone centered on the paraxial direction over highly-conducting irregular surfaces in an inhomogeneous atmosphere. For a complete review of this method, see the textbook of Levy (2000, IET, London) and the references therein. The great advantage of the PWE-SSF method is that it can deal with most real-life inhomogeneous environments and is that it fast (based on the calculation of successions of FFTs). Its main drawback is the underlying paraxial approximation leading to an approximation of the propagator (that is, the Green's function) and the boundary conditions are determined from a heuristic way, for instance from the Ament reflection coefficient (Ament, IRE, 1953). The well-known Method of Moments (MoM) is a way of solving rigorously the scattering problem by converting the Boundary Integral Equation (BIE) into a linear system, in which the impedance matrix must be inverted to determine the surface currents. Then, the scattered field is computed by radiating the surface currents. For a ducting environment, the main drawback of the MoM is that the Green's function (propagator) is known only for a small class of refractive index profiles. That is why, when the BIE method is applied, the propagator is usually derived under the PWE approximation. The duct effect is significant over a long distance, which means that the size (related to the surface length) of the linear system to solve is huge for practical applications. Combining three techniques, i.e., Subdomain Decomposition Iterative Method (SDIM), Adaptive Cross Approximation (ACA) and Forward-Backward Spectral acceleration (FBSA), a fast MoM is presented to efficiency calculate the propagation and scattering in ducting maritime environments. The resulting method is named ``SDIM+FBSA+ACA''. The SDIM allows us to split up the surface into sub-surfaces, the ACA allows us to accelerate the coupling steps between the sub-surfaces and FBSA allows us to accelerate the calculation of the local interactions on the sea sub-surfaces. The resulting complexity and memory requirement are then nearly proportional to N, the number of surface unknowns, whereas from a brute force of MoM, they are N3 and N2, respectively.
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Dates et versions

hal-01508413 , version 1 (14-04-2017)

Identifiants

  • HAL Id : hal-01508413 , version 1

Citer

Christophe Bourlier. Propagation and scattering in a ducting maritime environment from a fast method of moments. International Conference on Electromagnetics in Advanced Applications, Sep 2017, Verone, Italy. paper ID 119. ⟨hal-01508413⟩
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