Theory of acoustic measurement of internal wave strength as a function of depth, horizontal position, and time

Abstract

High‐frequency (≳ 1 cpd) variations in travel time of acoustic transmissions over ocean mesoscale distances are known to be dominated by the effects of internal wave displacements of the sound speed stratification (Flatté et al., 1979; Flatté, 1983 a ). Variations in the difference in travel time between transmissions in opposite directions along the same path (reciprocal transmissions) are dominated by internal wave currents [Munk et al., 1981]. We investigate the usefulness of a two‐mooring acoustic system for determining the statistical variances of internal wave displacements and currents as a function of depth, geographical position, and time. We find that Statistical fluctuations in the internal wave field itself prevent recovery of range‐dependent information between the two moorings. However, range‐averaged information can be obtained about mean energy level and about vertical energy migration. We find that uncertainties in the buoyancy and sound speed profiles do not significantly affect the usefulness of the method.