Time-domain simulations of outdoor sound propagation with suitable impedance boundary conditions

Finite difference time-domain methods are attractive for the study of broadband outdoor noise propagation, because they can accurately take into account both atmospheric and ground effects. Moreover, these methods allow moving sound sources to be modeled, which can be interesting in the context of transportation noise. A recently proposed method to obtain an impedance boundary condition is implemented in a linearized Euler equations solver. A long-range propagation configuration in a two-dimensional geometry is studied in homogeneous conditions and in downward-refracting conditions with an impedance ground over a distance of 500 m. Two impedance models corresponding to a grassy ground and to a snow-covered ground are considered. Numerical results are compared in the time domain to an analytical solution in homogeneous conditions and to results from a ray-tracing code in downward-refracting conditions. Near the ground, surface waves are detected in the two cases and are the dominant arrivals in the homogeneous case.