Computation of errors in current meters attached to near‐surface moorings

Abstract

Current measurements from moored buoy systems are contaminated by mooring motion. A few examples of moored buoy systems are studied to illustrate the use of computer simulations for computing errors introduced by surface waves in the current meters attached to near‐surface moorings. Results presented show that for all cases studied the standard deviations of true flow components (relative to the current meters) are greater than the standard deviations of wave orbital velocities, except near the surface. Also, in one case which is closest to a surface‐following mooring, the standard deviations of true flow components (relative to the current meters) increase, rather than decrease, with depth over the upper 40–45 m depth. Effect of mooring line characteristics, environment and vertical cosine response on the simulated current meter error is shown. In all cases, for current meters located near the ocean surface, the error is comparable to the surface wave induced Stokes drift. Significant errors (>1 cm s−1) were computed at depths greater (up to 2 and 3 times) than the depth where Stokes drift becomes negligible. Simulations also show a great deal of variation (several centimeters per second, the order of Stokes drift) in the error due to variations in mooring line characteristics and environments.