thumbnail

A modified beam-to-earth transformation to measure short-wavelength internal waves with an acoustic Doppler current profiler

Journal of Atmospheric and Oceanic Technology

By:
, , , ,
DOI: 10.1175/JTECH1731.1

Links

Abstract

The algorithm used to transform velocity signals from beam coordinates to earth coordinates in an acoustic Doppler current profiler (ADCP) relies on the assumption that the currents are uniform over the horizontal distance separating the beams. This condition may be violated by (nonlinear) internal waves, which can have wavelengths as small as 100-200 m. In this case, the standard algorithm combines velocities measured at different phases of a wave and produces horizontal velocities that increasingly differ from true velocities with distance from the ADCP. Observations made in Massachusetts Bay show that currents measured with a bottom-mounted upward-looking ADCP during periods when short-wavelength internal waves are present differ significantly from currents measured by point current meters, except very close to the instrument. These periods are flagged with high error velocities by the standard ADCP algorithm. In this paper measurements from the four spatially diverging beams and the backscatter intensity signal are used to calculate the propagation direction and celerity of the internal waves. Once this information is known, a modified beam-to-earth transformation that combines appropriately lagged beam measurements can be used to obtain current estimates in earth coordinates that compare well with pointwise measurements. ?? 2005 American Meteorological Society.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
A modified beam-to-earth transformation to measure short-wavelength internal waves with an acoustic Doppler current profiler
Series title:
Journal of Atmospheric and Oceanic Technology
DOI:
10.1175/JTECH1731.1
Volume
22
Issue:
5
Year Published:
2005
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
583
Last page:
591
Number of Pages:
9