Mode Coupling in VLF/LF Atmospheric Noise Models
Abstract
Tractable formulas are derived and tested for coupling among VLF/LF waveguide modes that occurs at boundaries separating regions of different ground conductivity. Although algebraically complicated, the formulas are easily programmed and require less computer running time than numerical mode-coupling algorithms used in exact computer codes. The formulas have two desirable features; (1) computational simplicity and (2) dependence on ground conductivity on either side of a transition (while depending only slightly on the conductivity variation within the transition itself). The formulas are subjected to three approximations, valid under most circumstances: (1) substitution of an equivalent parallel-plate waveguide for the actual waveguide in the short spatial interval that contains the conductivity boundary, (2) application of the WKB approximation, requiring that all conductivity changes in the transition zone be gradual (occurring over at least 1/6 wavelength), and (3) neglection of phase (only the magnitudes of the modes are used when performing certain numerical operations). Although derived for inclusion in future computer models of VLF/LF worldwide atmospheric noise, the mode-coupling formulas can be used in any application involving such a large number of propagation paths that the length of computer running time becomes a problem. Keywords: VLF/LF Propagation; Ground conductivity; Long-Wave communication; Strategic communication; Waveguide.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 31, 1987
- Accession Number
- ADA197639
Entities
People
- C. R. Warber
- E. C.