Theory of Ground-Wave Propagation Across a Rough Sea at Dekameter Wavelengths
Abstract
The effect of sea state on ground-wave propagation across the ocean is computed in the HF and VHF region. The history and present understanding of ground-wave propagation is briefly reviewed, especially as concerns the influence of roughness. The approach of the analysis is to derive an effective surface impedance at grazing which includes the effects of roughness. To do this, the statistical boundary perturbation approach of Rice is applied to the sea surface, which is 'slightly rough' at HF/VHF. In addition, the Leontovich (or impedance) boundary condition is employed because ocean water is a good (but not perfect) conductor at these frequencies. The analysis shows that the total effective impedance at the surface can be expressed as two terms: (1) the impedance of a perfectly smooth sea water surface at grazing, and (2) a second term accounting for roughness. The latter is obtained from the ocean wave-height spectrum. The report examines two height-spectrum models for wind-driven ocean waves: a directional Neumann-Pierson model and an isotropic Phillips spectrum. The effective surface impedance is calculated for these models. This impedance is then used to compute the ground-wave transmission loss across the sea. Graphs are shown for a variety of frequencies, ranges, sea states, and receiver heights. Examples, in which these curves are used in communications problems, are solved.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1970
- Accession Number
- AD0865840
Entities
People
- Donald E. Barrick
Organizations
- Battelle Memorial Institute