Sound propagation above an inhomogeneous impedance plane

Boundary integral equation (BIE) methods are described for the prediction of sound propagation, in particular from a line source, over a flat plane of inhomogeneous impedance. Approximate methods, which satisfy reciprocity, for the calculation of the wave field over a two-impedance plane are proposed. These approximations, applied to propagation from a line source, give results agreeing well with those of the BIE method. When they are applied to propagation from a point source, agreement with experiment is shown.