Oceanology International '96', Conference Proceedings, Volume 1, Held in Brighton, United Kingdom, on 5-8 March 1996. Environmental Factors Affecting the Acoustic Resonant Frequency Due to Internal Solitons

• Main Authors: Broadhead, Michael K, Field, Robert L
• Format: Publication
• Language: English
• Published: 26.11.1997
• Subjects: ACOUSTIC VELOCITY; ACOUSTIC WAVES; AIR WATER INTERACTIONS; AUDIO FREQUENCY; BIOLOGICAL OCEANOGRAPHY; ENVIRONMENTAL IMPACT; INTERNAL WAVES; LOW VELOCITY; OCEAN ENVIRONMENTS; OCEANS; PE62435N; PHYSICAL AND DYNAMIC OCEANOGRAPHY; RESONANT FREQUENCY; SHIFTING; SOLITONS; STRATIFICATION; SYMPOSIA; THERMOCLINES; UNDERWATER SOUND; UNITED KINGDOM; WAVE PACKETS

Nonlinear shallow water internal waves can enhance the bottom interaction of underwater sound. For a lossy ocean bottom, this has the effect of an overall level change (in addition to fluctuations) in the transmission loss at preferred ('resonant') frequencies. The mechanism for this effect is acoustic mode coupling due to the depression of higher sound speed water into lower speed water (at the pycnocline). It is also possible for this mechanism to induce a transfer of acoustic energy from below the thermocline into the mixed layer, and we concentrate on this scenario. One of the environmental effects on the length scale of the internal wave packet has been shown to be dissipation. The effect of this scale broadening on the resonant frequency is studied. Through rigorous simulations, it is shown that this effect produces a positive shift in the frequency line structure. Also offered is a simple model for this effect, based on mode coupling theory, that qualitatively predicts several features observed in the simulations.