Characterizing Along- and Cross-Channel Variability in Optical and Acoustic Backscatter During USRS Using AUVs
Abstract
During the ONR funded program called Under Sea Remote Sensing (USRS), we investigated optical and acoustic variability in three estuaries (Connecticut River, James River and Mobile Bay) using sensors mounted on REMUS100 Autonomous Underwater Vehicles (AUVs). Our most relevant and interesting data was collected using optodes (for dissolved oxygen), ADCPs (for bubbles inferred from acoustic backscatter) and turbidity sensors (for suspended sediments). The largest variability in opto/acoustic signals was found at estuarine fronts. The size, shape and movement of these fronts varied significantly depending on the bathymetry, tidal and freshwater forcing, and stratification. The major scatterers of light or sound were bubbles, especially at near surface fronts, and suspended sediments, especially at subsurface fronts, and likely microsalinity variability also was important wherever active mixing of fresh and saltwater occurred. We intensively sampled three fronts. One V-shaped tidal intrusion front was mostly stationary at the sea surface and setup just inside the estuary mouth during flood. Another C-shaped front had temporarily setup just outside the estuary mouth during ebb then swept over the coast ocean for several hours. The third Y-shaped front formed outside the estuary mouth as two fronts merged. Fronts connected to the sea surface had increased dissolved oxygen saturation in the newly formed mid-salinity waters produced by the front. Oxygenation resulted from the subduction of bubbles produced by wave steepening at the front, subduction of the bubbles by convergent flow at the front, and subsequent dissolution of the bubbles at increased hydrostatic pressure. Our observations imply that local estuarine fronts help oxygenate the coastal ocean. Large submerged bubble plumes at fronts also reduced acoustic transmission across the front resulting in degraded ACOMMS.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 28, 2023
- Accession Number
- AD1201228
Entities
People
- Andrey Y. Shcherbina
- Craig L. Mcneil
Organizations
- University of Washington