Temporal Variability of Seafloor Scattering and its Dependence on Environmental Parameters at Different Water Depths: Measurement and Models
Abstract
In the ocean, active sonar systems are used for the purposes of navigation, animal monitoring, object detection, hydrography, or sea-bed classification. Importantly, the performance of these systems depends on the acoustic properties of the seafloor. Seafloor properties are variable as they can be influenced by near-bottom hydrodynamics and biological activity occurring on various time scalessuch as: daily fluctuations due to biological benthic activity, hourly to weekly changes from storm events, seasonal cycles due to biological productivity and yearly to decadal variations caused by climate shifts. Such non-stationarity can significantly increase uncertainty in the performance of sonar systems used for object detection and classification as well as seabed classification. Previous work has primarily focused on the dependence of seafloor scatter on sediment type, transmit frequency and incidence angle. In comparison, few studies investigating temporal variations of seafloor scatter exist and those that do exist made measurements over short time scales (3 to 8 weeks). Thus, there is a critical need for improved characterization of seafloor scatter over longer time periods and its dependence on evolving environmental parameters, which can be used for inputs to scattering models and better sonar design as well as to increase our understanding of the performance of remote-sensing technologies.The overall goal of the proposed project is to measure the temporal and spatial variability of seafloor scattering at different water depths using high-frequency active acoustic systems to increase our understanding of the factors that impact it. To this end, a high-frequency active acoustic system (operating at 38 kHz, 70 kHz and 200 kHz) and a suite of other instruments measuring concurrent environmental parameters will be deployed on the seafloor in a series of experiments each lasting about 6 months in shallow water (about 20 m) off the coast of New Hampshire. Two other datasets containing measurements from the Gulf of Maine (200 m depth) and off the coast of central California (2000 m depth) will be obtained from related projects (Grants No. N00014231274 and N00014117585). The novelty of the proposed project liesin comparing long time series of calibrated acoustic scattering from different sites at varying depths (epipelagic, mesopelagic, bathypelagic) with differing sediment type, biological activity and near-bottom hydrodynamics to identify the main drivers influencingscattering strength and its temporal and spatial variability. Predictions from scattering models will be compared to the measurements to identify the mechanisms that are not properly captured by the models. The environmental measurements will be used as inputs tosediment transport models to identify times of sediment motion and sediment transport rates, which will be related to changes in local forcing conditions and scattering strength.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 09, 2024
- Source ID
- N000142412653
Entities
People
- Jenna Hare
Organizations
- Office of Naval Research
- United States Navy
- University System of New Hampshire