Wavefront intensity statistics for 284-Hz broadband transmissions to 107-km range in the Philippine Sea: Observations and modeling

Abstract

In the spring of 2009, broadband transmissions from a ship-suspended source with a 284-Hz center frequency were received on a moored and navigated vertical array of hydrophones over a range of 107 km in the Philippine Sea. During a 60-h period over 19,000 transmissions were carried out. The observed wavefront arrival structure reveals four distinct purely refracted acoustic paths: One with a single upper turning point near 80 m depth, two with a pair of upper turning points at a depth of roughly 300 m, and one with three upper turning points at 420 m. Individual path intensity, defined as the absolute square of the center frequency Fourier component for that arrival, was estimated over the 60-h duration and used to compute scintillation index and log-intensity variance. Monte Carlo parabolic equation simulations using internal-wave induced sound speed perturbations obeying the Garrett-Munk internal-wave energy spectrum were in agreement with measured data for the three deeper-turning paths but differed by as much as a factor of four for the near surface-interacting path.

The North Pacific Acoustic Laboratory deep-water acoustic propagation experiments in the Philippine Sea

“…The detailed results from these experiments, as well as related analyses, will appear in a series of papers, including at present Colosi et al (2013), Freeman et al (2013), Heaney et al (2013), Powell et al (2013), Van Uffelen et al (2013), and White et al (2013). The selected results presented here have emphasized the ambient noise measurements only because those analyses are among the more straightforward.…”

North Pacific Acoustic Lab and Deep Water Acoustics

“…The arrival corresponding to ray path ID-3 was windowed out from the resulting time fronts. This path exhibited intensity fades of 10 dB that lasted 18 and 12 h, respectively, in measurements obtained during PhilSea09 [2,3]. An example of the simulated intensity profile vs. depth for path ID-3 at 1-h intervals spanning 24 h is shown in figure 3.…”

A reformulation of the Λ−Φ diagram for the prediction of ocean acoustic fluctuation regimes

“…Finally, there is the 107-km, 2009 Philippine Sea experiment which transmitted 280 Hz pulses and observed acoustic fluctuations along four ray paths (White et al, 2013). For this experiment detailed internal wave observations were analyzed by Colosi et al (2013) where the GM model proved a reasonably good fit to the observations.…”

“…the Philippine Sea 2009 (PhilSea09) Experiment(White et al, 2013). The first two experiments show the largest fluctuations and therefore are associated most with the partial and full saturation regimes.…”