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75 kHz RDI Ocean Surveyor Evaluation:
Comparison with 150KHz Narrow Band,
R/V Endeavor, Feb. 17-23, 2001.
Draft document.
Jules Hummon - Eric Firing
Abstract:
During a recent transit from Florida to Rhode Island, simultaneous single-ping
data were recorded from two acoustic Doppler current profilers on the R/V
Endeavor: an old 150-kHz narrow bandwidth (NB) model, and a new 75-kHz
model (Ocean Surveyor: OS) with a flat phased-array transducer, operating
alternately in narrow bandwidth (OSN) and broad bandwidth (OSB) modes.
In calm weather the NB, OSN, and OSB data showed nearly perfect agreement,
but the range of the OSN (up to 800 m) was about twice that of the NB,
and the OSB range was about 85% of the OSN range. As weather worsened,
the returns from all three degraded, with reduced depth range and with
occasional pings returning no valid velocity estimates. Reduction in data
return was most severe in the OSB, least severe in the NB. Performance
degradation was associated with a velocity bias towards zero in both the
OSB and OSN relative to the NB; we believe this problem can be solved with
improved single-ping editing and averaging algorithms. Much larger velocity
bias occurred in OS bottom tracking data. Beam sidelobes were 12-15 db
higher in the OS than in the NB. Although this did not cause obvious velocity
profile errors in the present dataset, we believe it will do so in regions
such as the eastern equatorial Pacific.
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Next:Introduction
Jules Hummon 2001-10-24