Variance of Discharge Estimates Sampled Using Acoustic Doppler Current Profilers from Moving Platforms

Abstract

This paper presents a model for quantifying the random errors (i.e., variance) of acoustic Doppler current profiler (ADCP) discharge measurements from moving platforms associated with different sampling times. The model focuses on the random processes in the sampled flow field and has been developed using statistical methods that are currently available for the uncertainty analysis of velocity time series. Analysis of field data that were collected using ADCP from moving platforms from three natural rivers of varying sizes and flow conditions shows that, even though the estimate of the integral time scale of the actual turbulent flow field is larger than the sampling interval, the integral time scale of the sampled flow field is in keeping with the sampling interval. Thus, an equation for computing the variance error in discharge measurements associated with different sampling times, assuming uncorrelated flow fields, is appropriate. The approach is used to help define optimal sampling strategies by choosing the exposure time required for ADCPs to accurately measure flow discharge.