A line‐of‐sight propagation model for calculating atmospheric, sea, terrain multipath, and clutter at microwave frequencies

The two‐dimensional parabolic wave equation (PE) is solved asymptotically in order to derive a propagation/scattering model for propagation in a stratified atmosphere, together with scattering and diffraction from the sea/terrain surface, within line of sight. The asymptotic solution to the PE begins by expanding the unknown field in a Luneberg‐Kline expansion. The first‐order solution to the Luneberg‐Kline expansion yields the eikonal equation for the ray trajectory, and the second‐order solution yields the transport equation for the energy density of the rays along the trajectory. The solution to the eikonal and transport equations is used to derive an asymptotic result for the plane wave spectrum solution for the PE, referred to as the wave‐theoretic model. The asymptotic solution for the field shows the relationship between a properly directed tube of rays in the atmosphere satisfying the eikonal and conservation of energy equations and the same tube of rays striking an edge and being diffracted, as in the geometrical theory of diffraction (GTD). The solution for the eikonal yields the ray trajectory in the stratified atmosphere and therefore the grazing angle on the sea/terrain profile necessary for calculating multipath and clutter. Also, a new derivation for the backscatter from a deterministic sea/terrain profile is given which agrees with Collin's [1992] new full wave theory and at grazing reduces to the perturbation result with the correct polarization dependence. Incorporating the various electromagnetic propagation/scattering mechanisms in one model yields a prediction tool that can be applied to a large class of propagation/scattering problems such as the analysis of radar performance in a littoral scenario, or the performance of a line‐of‐sight communication link operating over irregular terrain.