Low-frequency ground wave propagation over narrow terrain features

Solutions of the one- and two-dimensional integral equations that describe ground wave propagation are presented and compared. The one-dimensional equation is shown to be inaccurate at low frequencies for obstacles narrower than about 10 km and typical pathlengths. In such cases, the two-dimensional equation is needed to account properly for the signal's dependence on obstacle width, recovery at long distances, and transverse diffraction pattern. The one- and two-dimensional solutions approach each other at large distances beyond very wide obstacles.