Quality Controlling Surf Zone Acoustic Doppler Velocimeter Observations to Estimate the Turbulent Dissipation Rate

Abstract

Abstract High-quality measurements of the turbulent dissipation rate ε are required to diagnose field surf-zone turbulence budgets. Quality control (QC) methods are presented for estimating surf zone ε with acoustic Doppler velocimeter (ADV) data. Bad ADV velocity data points are diagnosed with both the ADV signal strength (SS) and correlation (CORR). The fraction of bad SS data points (δSS) depends inversely upon the wave-amplitude-normalized transducer distance below the mean sea surface. The fraction of bad CORR data points δCORR can be elevated when δSS is low. The δCORR depends inversely upon the wave-amplitude-normalized sensing volume distance below the mean sea surface, and also increases with increased wave breaking, consistent with turbulence- and bubble-induced Doppler noise. Velocity spectra derived from both “patched” and “interpolated” time series are used to estimate ε. Two QC tests, based upon the properties of a turbulent inertial subrange, are used to reject bad ε data runs. The first test checks that the vertical velocity spectrum’s power-law exponent is near . The second test checks that a ratio R of horizontal and vertical velocity spectra is near 1. Over all δCORR, 70% of the patched and interpolated data runs pass these tests. However, for larger δCORR > 0.1 (locations higher in the water column), 50% more patched than interpolated data runs pass the QC tests. Previous QC methods designed for wave studies are not appropriate for ε QC. The results suggest that ε can be consistently estimated over the lower 60% of the water column and >0.1 m above the bed within a saturated surf zone.