PREDICTIONS OF TRAFFIC NOISE-PROPAGATION OVER A CURVED ROAD HAVING ANIMPEDANCE DISCONTINUITY WITH REFRACTING ATMOSPHERES

The polar parabolic equation (polar PE) method, which introduces bound ary fitting coordinates into the wide-angle parabolic equation (PE) me thod, was used to solve sound propagation over a curved surface and ov er irregular terrain. The polar PE and PE methods, which march the fie ld with matrix elements in range, can include sound propagation having range-dependent ground-surface and sound-speed profiles. The matrices should be updated at the discontinuous point to allow range-dependent sound propagation. The polar PE calculations were obtained for sound propagation over a curved surface, radius of curvature 200 m, having a homogeneous ground surface and a discontinuous ground surface. Those ground surfaces represent an all-asphalt road, asphalt to grass-covere d ground, and all-grass-covered ground. The discontinuous ground surfa ce, asphalt to grass ground, started 30 m from the acoustic source ove r an asphalt road. Calculations with no refracting atmosphere show tha t lawn-covered ground near the road reduces the traffic noise level to about 10 dB for 200 Hz and to about 20 dB for 300 Hz at a distance 20 0 m away from the source along the curved surface.