Spatial and temporal variability in biophysical processes and sound scattering at a long-term acoustic monitoring site
Abstract
Abstract (Approved for Public Release):High frequency (10s-100s kHz) underwater sound is a valuable tool used by marine mammals, scientists, and sonar operators to interrogate the marine environment. But in the complex ocean, there are a variety of both physicaland biological processes (Warren et al., 2003) which can affect the propagation of this energy, primarily through scattering processes. This study will investigate the combined effects of pelagic zooplankton and coastal ocean dynamics impact the temporal and spatial variability in acoustic backscatter near a long-term Gulf of Maine passive/active acoustic monitoring site. Proposed observations are designed to sample and assess the relative sound scattering impacts of macrozooplankton, nekton, and fish aggregations and their behavior (e.g. diurnal migrations) relative to semi-diurnal water column profile change driven by linear and nonlinear internal tidal forcing. The approach focuses on filling identified observational gaps meant to improve the interpretation of daily signalvariations observed near the Wilkinson Basin (AEON 5) Gulf of Maine monitoring station. This region is a highly dynamic area where the tide and complex bathymetry are central to the local circulation and ecosystem dynamics. One project component will be a dedicated spatial echosounder survey to resolve known km-scale variability in the internal wave and sound backscatter fields around this site in the late spring period where these combined biophysical controls are typically present. This shipboard sampling will also include in situ zooplankton and hydrographic survey data to quantify scatterer and water column spatial decorrelation scales in a 10 km2 area surrounding the site. Alongside this effort, high-rate fixed site sampling at 1 to 10 minute time scales will be used to characterize temporal variability that is not measured using the ongoing hourly AEON5 active acoustic time series. This will be done using a continuous vertical profiler and bottom-mounted ADCP measurements collected next to station AEON5. The time-series data will also address correlation and the sound scattering controls shared between observed spatial and temporal variability, as observed using combined ship-based and profiler-based observations surrounding this long-term site. Field work and data processing will be performed in the project s first year, with year two focused on data analysis documenting variability at these short scales, data product delivery, and better understanding the implications for existing and future soundscape monitoring networks in regions with similar coastal complexity.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 24, 2023
- Source ID
- N000142312740
Entities
People
- Doug Vandemark
Organizations
- Office of Naval Research
- United States Navy
- University System of New Hampshire