New England Seamount Calibrated Acoustic Fluctuation Experiment (NESCAFE)
Abstract
Scripps Institution of Oceanography (PI: Matthew Dzieciuch) proposes to conduct the New England Seamount Calibrated Acoustic Fluctua tion Experiment (NESCAFE), a Task Force Ocean (TFO) Department Research Initiative (DRI). The focus of NESCAFE is to understand and improve the acoustic propagation prediction capabilities of an ocean model in a highly dynamic region. The Gulf Stream crosses the e xperimental area and its influence will be challenging for both the ocean and the acoustic models. A pilot deployment has thus been proposed to validate the basic scales of variability before the main deployment. Planning for the experiment has revealed that chang es in the acoustic arrival pattern are expected to be large and occur rapidly. The changes are likely to violate the typical assumpt ion of linearity and will demand new methods to be developed. The most highly variable component is the upper few hundred meters of the ocean. This layer changes from well-mixed in the winter to stratified in the summer. The presence of the warm Gulf Stream leads to sharp fronts that move rapidly and significantly affect the sound speed. An acoustically important layer is the relatively warmer mode water at 18C that is located at about 100-500 m. This layer forms a thermopause, a region of weak thermocline gradient, embe dded in the stronger main thermocline. The weak temperature gradient leads to a weak sound speed gradient that transitions to a stro ng main thermocline gradient around 500 m. This transition zone between weak and strong gradients is associated with a rapid diverge nce of ray paths. Furthermore, since the mode water has a weak gradient, any perturbation due to Gulf Stream meanders, eddies, or in ternal waves can result in the formation of a subsurface or secondary acoustic duct that is located above the main thermocline. Soun d trapped in this layer will experience little loss but will also be highly variable as the mode water is modulated by the Gulf Stre am. The experimental geometry seeks to acoustically probe this layer and investigate the limits of our current measuring and modelin g capabilities. The main challenge of this experiment will be to see if the acoustic arrival pattern of the observations is predicta ble based upon the available environmental information? The environmental information can come from climatology, ocean models, or lo cal observations. For identified ray paths or ducted modes we seek to answer two further questions: 1) Can the acoustic observations be used to infer properties of the sound-speed profiles? and 2) Can we predict the statistics of the arrivals? The central question s are: How much environmental information is necessary to reliably predict the acoustic propagation observations? For what length of time can an ocean model skillfully predict the acoustic arrival patterns. What are the impacts on signal detection, coherence, and tracking?Our goal is to explore the fundamental limits of acoustic signal processing and to exploit the remote sensing capabilities of acoustics jointly with ocean models to characterize acoustic signal propagation. The data and skills obtained by this experiment will improve our ability to monitor, communicate, and navigate in one of the most highly dynamic parts of the ocean.Approved for Pu blic Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 07, 2021
- Source ID
- N000142112907
Entities
People
- Matthew A. Dzieciuch
Organizations
- Office of Naval Research
- United States Navy
- University of California, San Diego