The single axis sample volume of the BASS Rake acoustic current sensor

The BASS Rake is a differential travel time acoustic current meter designed to make spatially and temporally dense velocity profile measurements in the continental shelf wave bottom boundary layer (WBBL). The high levels of bottom shear stress common to the wave boundary layer are important contributors to the sediment entrainment process and strongly enhance the turbulent dissipation of energy in overlying steady boundary layers. The geometry of the acoustic axes of earlier BASS sensors made accurate determination of the sample volume over which velocity is averaged during a measurement unnecessary. However, the arrangement of BASS Rake acoustic axes, the small vertical scale of velocity profile curvature in the wave boundary layer, and the proximity of the fluid-sediment interface, make an accurate understanding of the averaging volume and the error it can introduce into a velocity measurement essential to the determination of sensor accuracy.