Environmental description for ambient noise prediction
Abstract
Ocean ambient noise, spanning from a few hertz to tens of kilohertz, is important and often the limiting factor for sonar performances to the fidelity of operational algorithms, and therefore demands understanding of the underlying physics of the noise field for prediction purposes.An overarching objective of the proposed effort is to fully understand the wind speed and frequency dependenciesof ambient sound level in response to environmental conditions such as wind speed, wave height/direction, and currents, identify mechanisms potentially causing the fluctuations in observed levels, quantify the reduction of ambient sound at higher sea-states and incorporate this understanding into a model for the resultant ambient sound field.A Passive Aquatic Listener (PAL) was deployed in the North Pacific from 20072012 at Ocean Station Papa (OSP). OSP is one of the NOAAs Ocean Climate Stations (NOAA-OCS). In six years, a total of 500,000 ambient noise samples, i.e., sound pressure level (SPL) in the frequency range of 100 Hz50 kHz, were obtained. Using surface meteorological data, ambient noise spectra were sorted under wind speed ranges of 13, 68, 1113, 1517, 1820, and2123 m/s, corresponding to surface agitation from calm to the start of wave breaking and to very rough seas.A considerable increase in SPL can be seen from 100 Hz40 kHz between the calm sea (13 m/s) and 68 m/s, when surface waves start to break. This across-the-board elevation in SPL starts to break down between 1113 and 1517 m/s cases, where a sharp drop-off for frequencies higher than3 kHz is observed and the SPL can fall below that of much lower wind speed. The most extreme is the 2123 m/s case: with a sharp faled in PAL data, however, cannot be described by ambient noise models such as CANARY, which predicts a monotonic SPL increase with wind speed for all frequencies. Another important feature to note is the spread of ambient noise samples about the mean values observed in this 6-year ambient noise data set, which is not addressed by current models. The spread will be a combination of short time period fluctuations and longer time period variability that is likely related to changes in the environment other than wind speed. This level of fluctuation is significant for operational purposes and it is worth investigating the cause(s) of such variations with the ultimate goal of incorporating such understanding in models.In this proposed 3-year effort, measurements of multi-year stationed deep water ambient noise, bubble plume backscatter/echo intensity, and surface meteide a description of how these three components interact with each other under almost all surface conditions. For ambient noise prediction, there is a need for a good description for the highly transient, time- and space-varying environment for a complete spectrum of environmental conditions, i.e., from the most benign dead-calm sea to severe storm cases. This is especially true for higher sea-state cases, where current models are unable to predict the wind speed and frequency dependencies of ambient sound levels. In addition to the analysis work of data from NOAA-OCS, this proposed work includes participation in the TFO field work at a shallow water site near the Washington coast where combined acoustic and oceanographic measurements are planned by investigators from APL-UW and NRL-SSC. Deep water ambient noise and bubble plume measurements would be repeated at the shallow water site (~150 m water depth) and would provide insight into the applicability of ambient noise generation and the dynamic bubble model developed over deep water to shallow water environments.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 06, 2021
- Source ID
- N000142112306
Entities
People
- Jie Yang
Organizations
- Office of Naval Research
- United States Navy
- University of Washington