The overtone structure of acoustic fluctuations due to harmonic variations in sound speed (L)

Abstract

Explicit relations are derived between the acoustic pressure and a sound speed that is periodic. They are derived for the Pekeris waveguide, and extended to the range and depth-dependent adiabatic mode/WKB case. As expected, acoustic pressure is found to fluctuate at the sound speed fundamental and its overtones. A Pekeris model simulation qualitatively agrees with the intensity fluctuation spectrum from a range and depth-dependent parabolic equation ͑PE͒ simulation of a shelf edge experiment off the New Jersey coast. In this paper we show that the energy of the higher overtones can be significant and derive a modulation index that determines the factors that contribute to the overtone energy.

Fluctuations in sound transmission through sound speed profiles that are periodic in range and geotime

“…2, for M = 0.1, very nearly corresponds to the rangeindependent case and reveals complex power variations indicating overtones of the fundamental period 12.42 h all along the water column. 4,8 As the value of M increases, the overtone structure decreases, as seen in the middle plot for M = 0.7. For M = 1.7 ͑bottom plot͒, the fluctuation is essentially that of the fundamental sound speed variation.…”