ABSTRACT
This chapter discusses models for predicting the effects of impedance changes along propagation paths and the resulting understanding of these effects. The strips were tightly packed to avoid gaps at the impedance discontinuities and the resulting mixed impedance surfaces were plane. A situation for a ground surface with single impedance discontinuity of equal proportion of both ground type inside the Fresnel zone is considered. K. B. Rasmussen has suggested a numerical method for determining the sound field over a plane containing an impedance discontinuity. Nevertheless, the Fresnel-zone method cannot differentiate between single and multiple impedance discontinuities. C. Nyberg has solved the Helmholtz equation with the boundary condition for a point source above an infinite plane surface consisting of strips with alternating impedance by using Cartesian coordinates and a Fourier transform technique. The modified De Jong model gives better agreement with the Boundary Element method predictions than the original De Jong model for a soft to hard impedance discontinuity.
