Fractal scattering indicators for urban sound diffusion
Résumé
Irregular surfaces like urban frontages produce an anomalous back-scattered region, creating an acoustic interference field in their neighborhood. Thus, in order to be able to detect that scattered energy's minima and maxima through taking the frontage morphological characterization into account, we propose a new measurement method of the building geometry, with using mathematical morphology techniques. Results of this geometrical approach provide two types of indicators, global and local. The global one, the structure factor of the urban frontage, is related to the multiscale characterization of the whole building geometry through the computation of the spatial Fourier transform of the scatterers. The complementary local indicator evaluates the vertex multiscale densitometrical distribution at each incidence angle, provided through a fractal evaluation technique, the Minkowski sausage. This densitometry computation reveals the characteristic directions of scattering, which has to be calculated through the scattering pressure function along the lateral active diffraction zone.
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