The authors develop a radiowave propagation prediction model suitable for use over irregular terrain in the VHF and UHF bands. Existing models are predominantly 2D and therefore take no account of terrain gradients transverse to the great circle path, obstacles to the side of the great circle path (such as hills) or propagation around the sides of obstacles. Their aim is to reduce these errors by developing a model which incorporates the 3D nature of the terrain. Many existing propagation prediction models use an idealised knife-edge representation of the terrain and this gross simplification is known to lead to large errors in certain situations. The parabolic equation (PE) method uses a more accurate representation of the terrain, as well as incorporating the surface impedance of the terrain.
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