APPLICATION OF THE GAUSSIAN-BEAM APPROACH TO SOUND-PROPAGATION IN THEATMOSPHERE - THEORY AND EXPERIMENTS

The Gaussian beam approach solves the wave equation in the neighborhoo d of the conventional rays using the parabolic approximation. 'rhe sol ution associates with each ray a beam having a Gaussian amplitude prof ile normal to the ray. The approximate overall solution for a given so urce is then constructed by a superposition of Gaussian beams along ne arby rays. The solution removes ray-tracing artifacts such as perfect shadows and infinite energy at caustics without the computational diff iculties of numerical solutions to the wave equation. In tliis paper, the Gaussian beam approach is applied to atmospheric sound propagation in the presence of refraction above a ground surface. A brief overvie w of the method is presented. Calculations obtained from Gaussian beam tracing are compared to those obtained from the fast field program (F FP) and to experimental measurements. The experiments were made above a concave surface indoors that simulates propagation under downward re fraction (inversion or downwind) in the cases of a hard and finite imp edance surface. These experiments include measurements in the presence of a barrier. Measurements were also made in a wind tunnel in the pre sence of wind and temperature gradients. The results suggest that beam tracing can be applied to complex atmospheric sound propagation probl ems with advantages over conventional ray tracing and full-wave soluti ons.