Upgrade of a Two Axis, Foward-Scatter, Laser-Doppler Velocimeter used in Flume Studies of Oceanographic Processes

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The Coastal Research Laboratory at the Woods Hole Oceanographic Institution will upgrade an aging two-axis, forward-scatter laser Doppler volicimeter (LDV). The LDV is mounted on a large 17-meter recirculating seawater flume that is used by a large number of investigators for a variety of projects. Several electronic and electro-optical components of the system have deteriorated over time due to the continual presence of salt aerosols and others have become obsolete. The flume provides a steady flow of recirculating seawater and experiments are set up in the flume to measure the fine-scale flow characteristics and turbulence fluctuations assoc- iated with the experiment. The LDV measures the Doppler frequency shift from two laser beams that are aimed into the flow. Advanced signal processing is used to derive detailed patterns of the flowing seawater. The use of flumes and LDVs for better under- standing flow characteristics is becoming increasingly important for studying oceanographic processes, especially within the bottom boundary layer. This upgrade will cost-effectively provide a state-of-the-art system that will be available for shared use.