Acoustic altimeter control of a free vehicle for near-bottom turbulence measurements

A 200 kHz acoustic altimeter was incorporated into the freely-falling High Resolution Profiler (Schmitt et al., 1988; Journal of Atmospheric and Oceanic Technology, 5, 484–500) for the control of weight release at dive-end for near-bottom approaches. The altimeter gave consistent returns within 100 m of the bottom. This has allowed controlled approaches to within 10 m of the bottom for the measurement of turbulence levels. Since near-bottom turbulence levels can be many orders of magnitude above those in the interior ocean, this capability permits study of the strongest mixing regions in the deep ocean.