ABSTRACT
This chapter considers the sound field due to a line source above a ground surface which is a two-dimensional problem often used to model highway noise. One of the interesting features of outdoor sound propagation over acoustically soft ground, for ground impedance conditions and geometries, is the existence of surface wave. Sound propagating from a point source over smooth flat acoustically soft ground can be idealized by the two-media problem. The lower medium is idealized as a homogeneous rigid-porous medium and treated as an effective fluid with complex density and propagation constant. The upper medium represents the homogeneous stationary atmosphere with constant uniform air density and speed of sound. The chapter gives a derivation of the classical expression for the sound field due to a monopole source above a locally reacting ground. The concept of effective admittance is extended from that for semi-infinite porous ground to that for a porous layer of finite thickness lying on a hard, impervious ground.
