Local intrinsic modes: Layer with nonplanar interface
Laterally inhomogeneous layered media serve as models for realistic propagation environments in electromagnetics, optics, underwater acoustics, seismology and other disciplines. When the inhomogeneities extend over long distances compared to the local wavelength, general methods (like those based on integral equations) for these nonseparable boundary value problems become intractable. For weak lateral variations, the propagation process can be localized around intrinsic modal fields, which are synthesized by plane wave spectra capable of describing propagation properties uniformly in guiding, cutoff and radiating regions. These local intrinsic modes, specified by modal invariants, traverse the medium along lateral trajectories, which may refract and form caustics similar to those for ordinary ray fields in an inhomogeneous environment. In the present investigation, these concepts are applied to a single homogeneous layer separated from a homogeneous half space by an interface with arbitrary but slowly changing profile, as exemplified by a shallow ocean waveguide. The previously derived intrinsic modes for a two- dimensional wedge geometry [the authors, J. Acoust. Soc. Am. 76, 850-860 (1984; Zbl 0563.76079)], serve as the prototype for the construction of the wave spectra, first, for the two-dimensional configuration with nonplanar interface, and then for the general three-dimensional case.
scientific article; zbMATH DE number 4018664
scientific article