Measurement Errors for Electromagnetic Current Meters

The Nearshore Sediment Transport Study (NSTS) field experiments relied on Marsh-McBirney electromagnetic current meters to provide estimates of currents in the surf zone, for modeling of both hydrodynamics and sediment transport. These meters were chosen because of their history of successful use in previous surf zone studies, relying on their compactness and durability in this rough environment. The present work was motivated by examination of the NSTS experimental data from Santa Barbara, California, in which the higher-order velocity moments calculated from current meter time series showed a time-variability not obviously related to time scales of change of forcing (e. g., wave groupiness, infragravity waves), and by field studies which show persistent offshore near-bottom flow which is not yet satisfactorily explained by nearshore circulation theories. Because of the importance of these quasi-steady flows and higher order velocity moments to sediment transport in the nearshore, the present study examined under carefully controlled laboratory conditions the dynamic response of electromagnetic current meters (EMCM) typically used for field experimentation.