Observations and Feynman path integral analysis of acoustic fluctuations from the 2010-2011 Philippine Sea experiment

Abstract

Six acoustic sources arranged in a pentagon with a central point transmitted broadband signals in the frequency range 200–300 Hz to a water column spanning vertical array in the Philippine Sea from Spring 2010 to Spring 2011. The propagation ranges were 128, 210, 224, 379, 396, and 449 km. Observations of phase and intensity variance as well as vertical coherence were obtained for several ray identified wavefronts. These observations are compared to Feynman path integral theory predictions utilizing Garrett-Munk internal wave spectral fits to in-situ measurements of temperature, salinity, and current. The observations and theory suggest that the three shortest ranges are in the unsaturated regime while the three longer ranges are in the partially saturated regime. Vertical coherence lengths are well predicted by theory. Implications for future experiments designed to observe internal wave spectra acoustically will be discussed. Six acoustic sources arranged in a pentagon with a central point transmitted broadband signals in the frequency range 200–300 Hz to a water column spanning vertical array in the Philippine Sea from Spring 2010 to Spring 2011. The propagation ranges were 128, 210, 224, 379, 396, and 449 km. Observations of phase and intensity variance as well as vertical coherence were obtained for several ray identified wavefronts. These observations are compared to Feynman path integral theory predictions utilizing Garrett-Munk internal wave spectral fits to in-situ measurements of temperature, salinity, and current. The observations and theory suggest that the three shortest ranges are in the unsaturated regime while the three longer ranges are in the partially saturated regime. Vertical coherence lengths are well predicted by theory. Implications for future experiments designed to observe internal wave spectra acoustically will be discussed.