Aquatic habitat mapping with an acoustic doppler current profiler: Considerations for data quality

Abstract

When mounted on a boat or other moving platform, acoustic Doppler current profilers (ADCPs) can be used to map a wide range of ecologically significant phenomena, including measures of fluid shear, turbulence, vorticity, and near-bed sediment transport. However, the instrument movement necessary for mapping applications can generate significant errors, many of which have not been inadequately described. This report focuses on the mechanisms by which moving-platform errors are generated, and quantifies their magnitudes under typical habitatmapping conditions. The potential for velocity errors caused by mis-alignment of the instrument's internal compass are widely recognized, but has not previously been quantified for moving instruments. Numerical analyses show that even relatively minor compass mis-alignments can produce significant velocity errors, depending on the ratio of absolute instrument velocity to the target velocity and on the relative directions of instrument and target motion. A maximum absolute instrument velocity of about 1 m/s is recommended for most mapping applications. Lower velocities are appropriate when making bed velocity measurements, an emerging application that makes use of ADCP bottom-tracking to measure the velocity of sediment particles at the bed. The mechanisms by which heterogeneities in the flow velocity field generate horizontal velocities errors are also quantified, and some basic limitations in the effectiveness of standard error-detection criteria for identifying these errors are described. Bed velocity measurements may be particularly vulnerable to errors caused by spatial variability in the sediment transport field.

Acoustic bed velocity and bed load dynamics in a large sand bed river

“…It must also be acknowledged that bed velocity data are subject to several sources of error. In particular, bottom track measurements are sensitive to errors related to the heterogeneous character of the near‐bed flow field [ Gaeuman and Jacobson , 2005]. If one is to continue to pursue the use of ADCP technology to measure bed load transport in sand bed systems, it must be assumed that unsatisfactory correlations with bed load samples are caused by the difficulty in obtaining accurate bed load samples more so than by deficiencies in the acoustic data.…”

Quantifying fluid and bed dynamics for characterizing benthic physical habitat in large rivers

“…in a tidal estuary with much lower flow‐ and bed‐velocities than in the lower Missouri River), with a higher‐frequency instrument from a different manufacturer. Comparisons between bed velocity measurements and the vertical distribution of water velocities also show that high bed velocities are associated with relatively high near‐bed water velocities (Gaeuman and Jacobson, 2005).…”

“…the velocity directions and/or magnitudes sampled in different beams are dissimilar) generates errors in the calculated velocity components. Although most of these errors will be rejected according to system quality‐control criteria, a small fraction of the errors will escape detection (Gaeuman and Jacobson, 2005). Thus, samples obtained in areas of complex flow or uneven topography may incorporate more false velocity readings than samples from areas of homogeneous flow.…”

Science information to support Missouri River <em>Scaphirhynchus albus</em> (pallid sturgeon) effects analysis

“…Data are archived and housed at CERC in Columbia, Mo., and are organized in a file structure (MRHHDS) sorted both geographically and temporally by major river segment and survey date within river segments. Single-beam, multibeam, and ADCP data were collected using standardized hydroacoustic collection methods (Elliott and others, 2004;Gaeuman and Jacobson, 2005;Reuter and others, 2008;DeLonay and others, 2012). Map reaches vary from 0.1 to 8 river miles, total approximately 330 river miles (with some overlap), and are distributed over a wide geographic range on the Lower Missouri River and Yellowstone River (table 14).…”