Laboratory Tests of a New Multi-frequency Coherent Doppler Profiler in Oscillatory Flow Boundary Layers

The last two decades have witnessed increasing use of acoustic remote sensing technologies for sediment dynamics measurements in aqueous environments. The approach is driven by the need to minimize disturbances to the fluidsediment interactions occurring at or close to the mobile bed. This requirement is especially critical in wave-dominated environments, since the wave bottom boundary layer is typically O(10) cm thick, and thus inaccessible to invasive measurement methods during active transport conditions. Motivated in part by the need to measure turbulent fluxes, and thus to obtain simultaneous, collocated measurements of suspended particle concentration and velocity, we have developed a multi-frequency coherent Doppler profiler capable of resolving the vertical structure of the wave bottom boundary layer on both wave period and turbulent time scales. Results are presented from laboratory experiments with this new system in oscillatory flow boundary layers over both fixed roughness and evolving sand ripples.