Observations of low-frequency, long-range acoustic propagation in the Philippine Sea and comparisons with mode transport theory

Tarun K Chandrayadula; Sivaselvi Periyasamy; John A Colosi; Peter F Worcester; Matthew A Dzieciuch; James A Mercer; Rex K Andrew

doi:10.1121/10.0000587

Observations of low-frequency, long-range acoustic propagation in the Philippine Sea and comparisons with mode transport theory

J Acoust Soc Am. 2020 Feb;147(2):877. doi: 10.1121/10.0000587.

Authors

Tarun K Chandrayadula¹, Sivaselvi Periyasamy¹, John A Colosi², Peter F Worcester³, Matthew A Dzieciuch³, James A Mercer⁴, Rex K Andrew⁴

Affiliations

¹ Department of Ocean Engineering, Indian Institute of Technology Madras, Adyar, Chennai 600036, India.
² Department of Oceanography, Naval Postgraduate School, 1 University Circle, Monterey, California 93943, USA.
³ Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.
⁴ Applied Physics Laboratory, University of Washington, Seattle, Washington 98105, USA.

PMID: 32113322
DOI: 10.1121/10.0000587

Abstract

The year-long Philippine Sea (2010-2011) experiment (PhilSea) was an extensive deep water acoustic propagation experiment in which there were six different sources transmitting to a water column spanning a vertical line array. The six sources were placed in an array with a radius of 330 km and transmitted at frequencies in the 200-300 Hz and 140-205 Hz bands. The PhilSea frequencies are higher than previous deep water experiments in the North Pacific for which modal analyses were performed. Further, the acoustic paths sample a two-dimensional area that is rich in internal tides, waves, and eddies. The PhilSea observations are, thus, a new opportunity to observe acoustic modal variability at higher frequencies than before and in an oceanographically dynamic region. This paper focuses on mode observations around the mid-water depths. The mode observations are used to compute narrowband statistics such as transmission loss and broadband statistics such as peak pulse intensity, travel time wander, time spreads, and scintillation indices. The observations are then compared with a new hybrid broadband transport theory. The model-data comparisons show excellent agreement for modes 1-10 and minor deviations for the rest. The discrepancies in the comparisons are related to the limitations of the hybrid model and oceanographic fluctuations other than internal waves.