SBIR Phase I: A Fiber-Optic, Simultaneous, Multi-Point Turbulent Kinetic Energy Rate Dissipation Sensor

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This Small Business Innovative Research Phase I project proposes a laser device for the measurement of the dissipation rate of turbulent kinetic energy in the sea as well as in the laboratory. The sensor would be valuable in a number of oceanographic/fluid dynamics applications. For example, since the dissipation rate scales typically with the third power of the friction velocity, it is the most sensitive measure of dynamics in the ocean bottom and surface boundary layers; it is similarly vital to observations in the ocean interior where mixing in the ocean is of strong fundamental interest as well as of applied interest in the study of carbon cycling via organic and geochemical particulate transport. The new sensor concept is based on the unbiased, direct estimation of acceleration variance for short-time segments, and subsequent conversion to spatial gradients using Taylor's hypothesis for each segment. The laser device will not only be able to operate from a fixed platform providing Eulerian measurements of dissipation, it is also suitable for much higher dissipation rates than can be measured with existing sensors. Finally, the capability proposed here will not only provide measurements at a single point, it will be a simultaneous multi-point sensor based on work in progress in another SBIR grant. Because of the combined capabilities of extension to Eulerian measurement, high range in dissipation rate and multi-point capability, the development could make significant contributions to a broad range of science in oceanography/fluid dynamics. The resulting instruments will also be useful in the study of dynamics of marine aggregates which are postulated to break apart depending on the dissipation microscales. The dissipation sensor resulting from this development will be of broad use of to scientists studying boundary layer processes on the ocean surface and bottom to other scientists studying biological primary productivity and its interaction with turbulence and to those studying mixing processes in the ocean interior.