Publication Date:
2022-05-25
Description:
Author Posting. © American Meteorological Society 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 22 (2005): 583–591, doi:10.1175/JTECH1731.1.
Description:
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.
Description:
A. Scotti was partially supported
by ONR Grants N00014-03-1-0553 and N00014-01-1-
0172, B. Butman and P. Alexander by the U.S. Geological
Survey, and R. Beardsley by the WHOI Smith
Chair and ONR Grant N00014-98-1-0210. S. Anderson
received partial support from ONR (Grant N00014-97-
1-0158). The Massachusetts Bay Internal Wave Experiment
was jointly supported by ONR and USGS.
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
