Vertical line array measurements of ambient noise in the North Pacific

Abstract

Shipping noise and wind are the dominant sources of ocean noise in the frequency band between 20 and 500 Hz. This paper analyzes noise in that band using data from the SPICEX experiment, which took place in the North Pacific in 2004–2005, and compares the results with other North Pacific experiments. SPICEX included vertical arrays with sensors above and below the surface conjugate depth, facilitating an analysis of the depth dependence of ambient noise. The paper includes several key results. First, the 2004–05 noise levels at 50 Hz measured in SPICEX had not increased relative to levels measured by Morris [(1978). J. Acoust. Soc. Am. 64, 581–590] at a nearby North Pacific site three decades earlier, but rather were comparable to those levels. Second, at 50 Hz the noise below the conjugate depth decreases at a rate of −9.9 dB/km, which is similar to the rate measured by Morris and much less than the rate measured by Gaul, Knobles, Shooter, and Wittenborn [(2007). IEEE J. Ocean. Eng. 32, 497–512] for the CHURCH OPAL experiment. Finally, the paper describes the seasonal trends in noise over the year-long time series of the measurements.

Spatial Vertical Directionality and Correlation of Low-Frequency Ambient Noise in Deep Ocean Direct-Arrival Zones

“…Figure 7 a–c depicts the frequency-wavenumber spectra of the total noise field for wind speeds of 3, 7 and 12 m/s. Frequency-wavenumber diagrams [ 15 , 16 ] were utilized to examine the vertical directionality of the ambient noise field. The dominant noise sources reaching the VLA with shallow grazing angle close to horizontal direction are originated by distant ships when the wind speed was 3 m/s.…”

“…Naughton presented the results where the decrease in amplitude of the noise correlation function with increased separation followed the power law on a set of free-floating oceanic receivers whose relative positions varied with time [ 14 ]. The method of frequency-wavenumber diagrams was used to examine the statistic and directional properties of ambient noise in North Pacific [ 15 , 16 ]. The parabolic equation solution method was applied to build the model of the vertical correlation and vertical directionality of ocean ambient noise field under the slope, seamount and varying sound speed profile environments [ 17 ].…”

Long-term statistics and wind dependence of near-bottom and deep-sea ambient noise in the northwest South China Sea

“…Long-term statistics of ocean ambient noise have been investigated at plenty of locations in the global ocean, ranging from tropical/subtropical Pacific region (Farrokhrooz et al, 2017;Niu et al, 2021;Yang et al, 2023) and South China Sea (Da et al, 2014;Jiang et al, 2017;Shi et al, 2019), and temperate North Pacific region (McDonald et al, 2006;Seger et al, 2015;Schwock and Abadi, 2021), to polar region (Chen and Schmidt, 2017;Bonnel et al, 2021;Mo et al, 2023). The motivation of these previous works is to acquire the diel, monthly or seasonal variations of ambient noise in different areas, and describe the relationship between noise and meteorological data at the recording locations.…”

The analysis of the depth dependence of ambient noise in the South China Sea

“…Najeem [5] et al conducted two months of ocean ambient noise observations in the shallow water of the Arabian Sea, and analyzed the vertical coherence structure of the noise field in the frequency range of 500Hz-5kHz. Mehdi [6] et al reported ambient noise measured by vertical arrays deployed during the 2004-2005 SPICEX experiments. The paper used a year-long data set to study noise in the 20-450Hz frequency band in the deep-water environment of the eastern North Pacific.…”