INSTRUMENTATION

The Advanced Plume Sensor System is a multi-sensor package designed to probe the structure of the dense bubble plumes beneath ocean whitecaps on several simultaneous spatial scales. The instrument package includes:

These sensors simultaneously measure the bubble size distribution and void fraction of air within whitecap plumes, the size of the plumes and scaling of plume size with sea state, the acoustical roughness scales of the plume boundaries and the noise radiated during plume formation.

APEX OBSERVATIONS

Wave-induced bubble plumes are important in the following areas of acoustics:

Despite the central role in these areas, little is known about the physical properties of dense bubble plumes in the first few seconds following wave breaking. The advanced plume sensor system is designed to provide information of the measurement of plume scale, roughness and bubble sizes.

APEX provides principal observations of bubble plume structure necessary for high frequency scattering and noise models during high wind conditions (>20 knots). The overall objective is to generate physics-based models of plume generation and internal structure, and relate these to their observed acoustical properties.

In addition to providing valuable information about open-ocean induced bubble plumes, APEX can be deployed in the surf zone to characterize the acoustical cross-sections of surf-induced bubble plumes.

APEX DESIGN

APEX consists of the instrumentation package described above mounted onto two surface-following frames. The principal frame supports Doppler sonars and ring conductivity sensors co-located on a vertical array to simultaneously measure the void fraction of air and water turbulence during a breaking wave event. The laser-based imaging system and optical bubble counter are positioned adjacent to the vertical array to measure bubble size distributions and the bubble plume boundary at a fixed depth. The principal frame also supports PC104-based data acquisition computers to power and control the measurement instrumentation. All instrument computers are connected to a network, which is cabled to control station through a single umbical. All systems can be remotely integorrated and controlled from the control station.
A secondary frame, remote from but cabled to the primary frame, supports the acosutical scattering cross-section measurements.

DEPLOYMENTS

APEX has been deployed on numerous experiments. APEX was deployed in the winter of 2002 at the Martha’s Vineyard Coastal Observatory (MVCO) during the SPACE02 experiment funded by the ONR Ocean Acoustics Program and hosted by Dr. James Preisig at Woods Hole Oceanographic Institution. Collaborators included Dr. David Farmer at the Graduate School of Oceanography, University of Rhode Island and Dr. Svein Vagle from the Institute of Ocean Sciences, British Colombia.

For further information please see the APEX documentation in the Technology section of the IMT Laboratory website.

PUBLICATIONS

Grant B. Deane and M. Dale Stokes, “Scale dependence of bubble creation mechanisms in breaking waves”, Nature, Vol. 418, pp.839-844 (2002). (PDF Format 408K)