Book Description
This report develops and applies a practical method for analyzing long-wave propagation under conditions where the properties of the earth-ionosphere waveguide change markedly over lateral distances comparable to a wavelength or Fresnel zone. Full-wave solutions are used to describe both the vertical and horizontal dependences of the fields, but certain compromises are made to achieve tractability. The method is thus characterized as quasi-full-wave. Its main limitation is that the equation describing the vertical dependence is assumed to nearly decouple from the equation governing the lateral dependence. The method is valid at any frequency for which waveguide modes describe terrestrial propagation. Nonetheless, its practical utility is probably limited to ELF because the lateral properties of the earth-ionosphere waveguide are usually gradual enough to permit use of the WKB approximation at higher frequencies. To facilitate numerical solution, the lateral equation is transformed into an integral equation that accounts for most full-wave properties, including diffraction around a localized disturbance and reflection from lateral gradients. Numerical solutions based on model disturbances having lateral gradients in the direction of propagation reveal a standing wave pattern in front of the disturbance.
