Using a broadband ADCP in a tidal channel. Part II: Turbulence

A four-transducer, 600-kHz, broadband acoustic Dopple current profiler (ADC P) was rigidly mounted to the bottom of a fully turbulent tidal channel wit h peak Rows of 1 m s(-1). Rapid samples of velocity data are used to estima te various parameters of turbulence with the covariance technique. The ques tions of bias and error sources, statistical uncertainty, and spectra are a ddressed. Estimates of the Reynolds stress are biased by the misalignment o f the instrument axis with respect to vertical. This bias can be eliminated by a fifth transducer directed along the instrument axis. The estimates of turbulent kinetic energy (TKE) density have a systematic bias of 5 X 10(-4 ) m(2) s(-2) due to Doppler noise, and the relative statistical uncertainty of the 20-min averages is usually less than 20%-95% confidence. The bias i n the Reynolds stress due to Doppler noise is less than +/-4 X 10(-5) m(2). The band of zero significance is never less than 1.5 X 10(-5) m(2) s(-2) d ue to Doppler noise, and this band increases with increasing TKE density. V elocity fluctuations with periods longer than 20 min contribute little to e ither the stress or the TKE density. The rate of production of TKE density and the vertical eddy Viscosity are derived and in agreement with expectati ons for a tidal channel.