A submersible three-dimensional particle tracking velocimetry system for flow visualization in the coastal ocean

A submersible three-dimensional particle tracking velocimetry (3D-PTV) system has been developed to investigate the form and dynamics of coherent vortical structures within the bottom boundary layer of the coastal ocean. The system consists of four high-resolution digital cameras operating simultaneously to record the tracks of naturally occurring suspended particles within a 20 x 20 x 20 cm sample volume. The system has been deployed close to the seabed in Plymouth Sound, UK, and data recorded at 25 Hz in 20 min duration bursts. On average, about 150 particles can be tracked within the sample volume for durations in excess of 2.4 s ( 60 frames). Instantaneous three- dimensional velocity fields show that moderate flows within the tidal bottom boundary layer are mostly quiescent and interspersed by coherent vortices, consistent with previous observations using other techniques.