Calculation of Winds Induced Bottom Wave Orbital Velocity Using the Empirical Mode Decomposition Method

Abstract

AbstractAccurate bottom wave orbital velocity (BWOV) calculation is important for understanding critical dynamic processes (e.g., turbulent mixing, sediment transport) at the bottom boundary layer of the oceans. Here we first use the empirical mode decomposition (EMD) method to calculate BWOV and evaluate its performance by comparing with two conventional methods (spectra and velocity methods) using field measurements collected from an acoustic Doppler velocimeter (ADV). The results suggest that BWOVs calculated by the EMD method were well correlated (R2 ≥ 0.97) to the results by the other two methods but with a few percent discrepancies. Under strong wavy conditions, BWOVs from the EMD method were 8% and 6% smaller than those from the spectra and velocity methods, respectively. Under weak wavy conditions, BWOVs from the EMD method were 14% and 11% smaller than those from the spectra and velocity methods, respectively. Statistical distributions of BWOV suggest that the EMD method calculated instantaneous BWOVs and BWOV amplitudes closely matched the Gaussian and Rayleigh distributions, respectively. Uncertainty analysis suggests that the EMD method was capable of calculating the most accurate BWOVs among the three methods. While the spectra and velocity methods can provide robust BWOV estimation, they cannot completely avoid the errors caused by wave-unrelated motions and instrumental noise.