Response characteristics of the neutrally boyant float

Abstract

The response characteristics of the neutral buoyant vertical current meter are discussed primarily from a theoretical point of view. Computations are presented to illustrate the useful range and limitations of present instruments. Three aspects of the response are considered separately: rotational, vertical, and tilting due to vertical shear. The rotational response at low frequencies is poor only for very weak vertical currents due to viscous drag. At high frequencies the response is uniformly limited by the moment of inertia of the instrument. The vertical response is best in neutrally stable water. In highly stratified water, on the other hand, the response deteriorates for all frequencies because of the small relative flow past the instrument. In all cases it is limited at high frequencies because of instrument inertia.