Assessment of single-instrument techniques for removing wave bias from Reynolds stress estimates

Abstract

A new single-instrument method for removing wave bias from Reynolds stress estimates is proposed. Assuming that the wave motions and the pressure signal are spatially coherent, the method uses a linear filtration scheme to estimate the wave velocity at the instrument based on the pressure signal, and then the estimated velocity is subtracted from the measured velocity to arrive at a wave-free estimate of the Reynolds stress. The advantage of the proposed single-instrument technique is that it limits the financial and logistical issues associated with deploying a second instrument. The proposed method is compared to two frequency-domain-based single-instrument techniques and to a two-instrument method that uses the velocity signal at an adjacent instrument in a linear filtration scheme to estimate and remove the wave velocity. The methods are tested and compared using synthetic time series and field data collected in tidally driven shallow water flow in Wassaw Sound, Georgia and in deeper water currents in Monterey Bay, California. The method proposed in this study offers superior performance over the other single-instrument techniques in shallow water, comparing favorably with the two-instrument method. In deeper water, no single-instrument technique offers clearly superior performance.