Fluid mechanical measurements within the bottom boundary layer during coastal mixing and optics

Abstract

To quantify and understand the role of vertical mixing processes in determining mid-shelf vertical structure of hydrographic and optical properties and particulate matter, the Office of Naval Research (ONR) funded a program called Coastal Mixing and Optics (CMO), which was conducted at a mid-shelf location in the Mid-Atlantic Bight, south of Martha's Vineyard, Massachusetts. As part of the CMO program, a tall tripod, called 'SuperBASS,' was equipped to collect a year-long, near-bottom time-series of velocity, temperature, salinity and pressure. The BASS sensors were modified to measure absolute as well as differential acoustic travel time, to provide sound speed (a surrogate for temperature) and velocity in a single sample volume. Seven BASS velocity and time travel sensors were placed between 0.4 and 7 meters above bottom. Three acoustic Doppler velocity (ADV) meters were mounted near the bottom-most BASS sensors at 0.3 meters above bottom. The sensors were used to obtain high-quality time-series measurements of velocity and temperature throughout a large fraction of the bottom bondary layer on the New England shelf. The measurements provide vertical structure of the Reynolds-averaged velocity and temperature fields, direct covariance estimates of turbulent Reynolds stress and turbulent heat flux, and indirect inertial range estimates of dissipation rate for turbulent kinetic energy and temperature variance. The purpose of this report is to describe the SuperBASS instrumentation and deployments, to provide summaries of the data collected, and to document the processing, preliminary analysis and archival of data collected for this component of the program.