Avoiding biased data during real time HADCP data collection

In recent years, there has been an increase in the use of horizontally oriented acoustic Doppler current profilers (HADCPs) for real time data collection within vessel traffic safety programs. This paper summarizes a comparison between a barge mounted HADCP and a vessel mounted ADCP in the Delaware estuary in May 2004. A rigorous investigation of the influence of passing vessels and the presence of the bottom boundary on the HADCP data is presented along with a proposed method for detecting and excluding biased data prior to use in real time systems. The HADCP data were compared with vessel mounted ADCP data collected at various ranges along the HADCP profile. Comparisons between the two measurements were used to identify bias in the velocity from the HADCP where the beams began to interact with the local bathymetry. During periods when vessels passed through the three acoustic beams velocity and data quality indicators from the HADCP were also evaluated. The goal was to identify the magnitude of water velocity bias and the corresponding signature in the data quality assurance parameters. A method using standard quality assurance parameters is proposed to screen environmental bias and produce unbiased velocity estimates during real time data collection.