Long Wavelengths in Stratified Media: Comparisons between Theory and Experiment

Abstract

A principal characteristic of propagation in a medium of rapidly varying properties is its strong dispersion. For a transient source this means a rapidly changing form of the traveling wave. For simple harmonic excitation it results in different rates of energy transport for different frequencies and thus in resonant and antiresonant excitation frequencies. Both types of phenomena have been studied experimentally, although most of the past work has been limited to the dispersion of pulses, and in particular to the concept of “arrival time” of the various Fourier components. This concept, although not rigorous, has been very useful and has found many applications and verifications in geophysics and acoustics. In the last five years successful efforts have been made to obtain more detailed agreement between theory and experiment, with particular reference to the quantitative prediction of sound fields and wave forms. Several such experiments will be discussed here. One of these is a model experiment with a transient source, designed around Pekeris' treatment of the two-layered haft-space. Another is a simple harmonic experiment carried out in shallow water at sea. In both cases detailed and quantitative agreement has been secured within quite acceptable limits of error.