Quality control of acoustic Doppler velocimeter data in the surfzone

Acoustic Doppler velocimeter measurements in the surfzone can be corrupted by bubbles and suspended sediment, lack of submergence during the passage of wave troughs, biofouling, blockage (e.g., from kelp on instrument mounting frames) of the flow field near the current meter or of the path between the sampled fluid volume and the acoustic transducers, and by insufficient distance between an accreting seafloor and the sample volume. Individual bad acoustic Doppler velocity values can be detected (and subsequently replaced) from low along-beam signal-to-noise ratios and from low coherence between successive acoustic returns used to estimate velocity. In addition, corrupted data runs can be identified from ratios of pressure to velocity variance that deviate from linear theory, and from low coherence between time series of collocated pressure and wave-orbital velocities. Unmeasured vertical tilts of a current meter can be estimated from horizontal and vertical velocities, and corrected for numerically.