Comprehensive ambient noise measurements and prediction
Abstract
Ocean ambient noise, in the frequency band of a few hundred hertz to about 20 kHz, is mainly due to bubbles generated from surface breaking waves due to wind forcing. Supported by TFO (Grant N000142112306), two-decades of ambient noise data have been used to validate ambient noise models (Yang et al., 2023). Data-model comparisons show a mismatch, as existing models including the Wenz curves (Wenz, 1962) are monotonic in nature, while the ambient noise level has a sharp drop-off as wind speed exceeds 15 m/s for frequency higher than 3#4 kHz, which is hypothesized due to the attenuation of ambient noise generated near the sea surface propagating through the bubble plumes underneath breaking waves.To correctly model ambient noise for all weather conditions, two prerequisites are needed: wind-induced bubble plume dynamics and the resultant ambient noise vertical distribution. The former capability, supported by TFO and NOAA, is already in place. A DURIP proposal has been submitted for a vertical line array (VLA) to measure year-long ambient noise vertical distribution, but prospects for that proposal are presently uncertain. A line of work is proposed here with existing and new ambient noise measurements that should become available in the next several years. The focus (without the vertical line array) will be on developing and extending ambient noise empirical models that reduce prediction uncertainty. If the proposed VLA does become available this year or later, our goal will be to extend this effort to include measurements of ambient noise vertical distribution to improve prediction for noise propagation in arbitrary sound speed profiles, important for noise notch prediction. This proposed work is a data-driven and modeling-ensuing effort. All data sets here, including available, ongoing, and future data collection, are the first of its kind and haven#t been carried out before, re conditions including residence time at sea, coverage of weatherconditions, completeness of acoustic, oceanographic, and environmental measurements. In this proposed 3-year effort, the long-term goal is to model wind-induced ocean ambient noise more accurately in the frequency band of 1#20 kHz. The initial empirical model uses only wind speed, but many other aspects of the environment can affect the ambient noise level, such as wind history, current/direction, surface wave height, and bubble plume dynamics. Bubble plume statistics will be investigated between bubble cloud depth, frequency of occurrence, and residence time with environmental parameters, including wind speed/duration, current/direction, and surface wave height. The goal will be to determine if ambient noise prediction uncertainty can be reduced by including a more comprehensive description of the environment. Rigorous ambient noise modeling groundwork will be laid out using both bubble statistics and other environmental descriptors. For more advanced models that include other aspects of the environment, ambient noise modeling will be important for covering regions of environmental parameter space that are not included even in year-long data sets, and for extending predictions beyond the range of the environmental parameters encountered.It is also desirable to extend deep ocean measurements of ambient noise, bubble field structure, and environmental parameters to shallow water, a more complicated and bathymetric-, fetch-, and wind duration-limited environment to investigate the relative importance of environmental parameters in shallow water ambient noise prediction. This part of the effort is related to the proposed TFO Washington Shelf Experiment in 2025. Vertical line arrays from Scripps, echo sounder, and other environmental measurements will be available at the experiment to provide insight into the differences of ambient noise characteristics from deep to shallow water and the practicality of applying deep water ambient noise models to shallow water environments.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 09, 2024
- Source ID
- N000142512006
Entities
People
- Jie Yang
Organizations
- Office of Naval Research
- United States Navy
- University of Washington