An official website of the United States government
Humpback whale breathing-related sounds were recorded on elements of a coherent hydrophone array subaperture deployed vertically at the Great South Channel on the US Northeastern continental shelf in Fall 2021, where half of the hydrophones were in-air and the rest submerged underwater. In-air hydrophones recorded breathing sounds with approximately 2.5 s duration, but smaller bandwidths compared to underwater hydrophones where signal energies extended beyond 50 kHz, and a mean underwater source level of 161 ± 4 dB re 1 μPa at 1 m, based on measurements at 22.9 m. The underwater recorded humpback whale breathing sound spectra displayed a broadband dip centered at 15.7 kHz, with approximately 400 Hz half-power bandwidth, likely caused by attenuation from propagation through pulsating air bubbles. The air bubble radius for natural frequency of oscillations at 15.7 kHz is estimated to be 0.205–0.21 mm. These bubbles are capable of removing energy from the forward propagated humpback breathing sounds via resonance absorption most pronounced at and near bubble natural oscillation frequency. Humpback whale distances from the vertically deployed hydrophones are estimated and tracked by matching the curved nonlinear travel-time wavefront of its breathing sounds, since the whale was in the near-field of the subarray.
more »
« less
Underwater Acoustics for All: Expanding Capacity with Education and Low-Cost Sensors
Sound is a persistent yet dynamic component of the marine environment, reflecting both physical and biological properties. Whereas light can only travel tens of meters in the ocean, sound is able to travel tens to thousands of kilometers under certain conditions, revealing information at specific times and places. In addition, underwater sound provides opportunities for sustainable development and blue economy growth that aren’t readily available with other technologies. For example, the melting rate of Arctic ice and the health of coral reefs can be estimated from acoustic measurements (Becker et al., 2023). However, underwater acoustics is a complex topic, requiring specialized education and equipment. To expand the capacity of underwater acousticians requires dedicated educational opportunities and low-cost equipment and analysis resources.
more »
« less
- Award ID(s):
- 2318309
- PAR ID:
- 10599694
- Publisher / Repository:
- The Oceanography Society
- Date Published:
- Journal Name:
- Oceanography
- ISSN:
- 1042-8275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The time-dependent spectral characteristics of underwater sound radiated by an ocean vessel has complex dependencies on ship machinery, propeller dynamics, hydrodynamics of ship exhaust and motion, as well as ship board activities. Here the underwater sound radiated by a ship equipped with a controllable pitch propeller (CPP) is analyzed and quantified via its (i) power spectral density for signal energetics, (ii) temporal coherence for machinery tonal sound, and (iii) spectral coherence for propeller amplitude-modulated cavitation noise. Frequency-modulated (FM) tonal signals are also characterized in terms of their frequency variations. These characteristics are compared for different propeller pitch ratios ranging from 20% to 82% at fixed propeller revolutions per minute (RPM). The efficacy and robustness of ship parameter estimation at different pitches are discussed. Finally, analysis of one special measurement is provided, when ship changes speed, propeller pitch and RPM over the duration of the measurement. The 50% pitch is found to be a crucial point for this ship about which tonal characteristics of its underwater radiated sound attain their peak values, while broadband sound and associated spectral coherences are at a minimum. The findings here elucidate the effects of pitch variation on underwater sound radiated by ships with controllable pitch propellers and has applications in ship design and underwater noise mitigation.more » « less
-
Metamaterials have offered unprecedented potentials for wave manipulations. However, their applications in underwater acoustic wave control have remained largely unexplored. This is because of the limited material choices and the lack of reliable fabrication techniques for the complicated structures. Herein, a metamaterial with microlattice structures as the building blocks is proposed for underwater operations. By designing the building blocks of the metamaterial and assembling them in a layered fashion, anisotropy is embedded in the structure, which results along different effective sound speeds in orthogonal directions. The designed metamaterial is fabricated by metal additive manufacturing using aluminum and steel. Experiments are performed using a resonator tube to evaluate its performance in water. An anisotropy ratio of around 2 is achieved, which is in good agreement with numerical simulations. The proposed metamaterial provides an effective means for underwater sound control with reduced fabrication difficulties and increased service life.more » « less
-
Abstract Rain in tropical cyclones is studied using eight time series of underwater ambient sound at 40–50 kHz with wind speeds up to 45 m s−1beneath three tropical cyclones. At tropical cyclone wind speeds, rain- and wind-generated sound levels are comparable, and therefore rain cannot be detected by sound level alone. A rain detection algorithm that is based on the variations of 5–30-kHz sound levels with periods longer than 20 s and shorter than 30 min is proposed. Faster fluctuations (<20 s) are primarily due to wave breaking, and slower ones (>30 min) are due to overall wind variations. Higher-frequency sound (>30 kHz) is strongly attenuated by bubble clouds. This approach is supported by observations that, for wind speeds < 40 m s−1, the variation in sound level is much larger than that expected from observed wind variations and is roughly comparable to that expected from rain variations. The hydrophone results are consistent with rain estimates by the Tropical Rainfall Measuring Mission (TRMM) satellite and with Stepped-Frequency Microwave Radiometer (SFMR) and radar estimates by surveillance flights. The observations indicate that the rain-generated sound fluctuations have broadband acoustic spectra centered around 10 kHz. Acoustically detected rain events usually last for a few minutes. The data used in this study are insufficient to produce useful estimation of rain rate from ambient sound because of limited quantity and accuracy of the validation data. The frequency dependence of sound variations suggests that quantitative rainfall algorithms from ambient sound may be developed using multiple sound frequencies. Significance StatementRain is an indispensable process in forecasting the intensity and path of tropical cyclones. However, its role in the air–sea interaction is still poorly understood, and its parameterization in numerical models is still in development. In this work, we analyzed sound measurements made by hydrophones on board Lagrangian floats beneath tropical cyclones. We find that wind, rain, and breaking waves each have distinctive signatures in underwater ambient sound. We suggest that the air–sea dynamic processes in tropical cyclones can be explored by listening to ambient sound using hydrophones beneath the sea surface.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5670/oceanog.2025.107
