| Groundwave height-gain functions near a shoreline - :11212 | Office of Oceanic and Atmospheric Research (OAR)
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  • Description:
    A saddlepoint approximation to a Kirchhoff integration over the surface of the Earth is used to derive formulas for the groundwave field for an elevated observer near a shoreline. It is shown that the transition from homogeneous groundwave propagation to mixed-path groundwave propagation occurs not at a vertical plane above the shoreline, but rather at an oblique surface tilted in the direction of propagation. Thus, close enough to the shoreline and high enough, the field over land (for sea-to-land propagation) will not be affected by the land beneath the observer, so that the field is represented in terms of sea-type groundwave modes (with the associated height-gain functions) even though the observer is above the land. This phenomenon is explained by interpreting groundwave modes as ground-reflected waves. There is a transition region (of several hundred kilometers horizontally for HF propagation) where diffractive corrections must be made because of the location of the shoreline.

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