Accuracy of acoustic velocity metering systems for measurement of low velocity in open channels

Laenen, Antonius; Curtis, R. E., Jr.

Abstract:

Acoustic velocity meter (AVM) accuracy depends on equipment limitations, the accuracy of acoustic-path length and angle determination, and the stability of the mean velocity to acoustic-path velocity relation. Equipment limitations depend on path length and angle, transducer frequency, timing oscillator frequency, and signal-detection scheme. Typically, the velocity error from this source is about +or-1 to +or-10 mms/sec. Error in acoustic-path angle or length will result in a proportional measurement bias. Typically, an angle error of one degree will result in a velocity error of 2%, and a path-length error of one meter in 100 meter will result in an error of 1%. Ray bending (signal refraction) depends on path length and density gradients present in the stream. Any deviation from a straight acoustic path between transducer will change the unique relation between path velocity and mean velocity. These deviations will then introduce error in the mean velocity computation. Typically, for a 200-meter path length, the resultant error is less than one percent, but for a 1,000 meter path length, the error can be greater than 10%. Recent laboratory and field tests have substantiated assumptions of equipment limitations. Tow-tank tests of an AVM system with a 4.69-meter path length yielded an average standard deviation error of 9.3 mms/sec, and the field tests of an AVM system with a 20.5-meter path length yielded an average standard deviation error of a 4 mms/sec. (USGS)

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USGS Numbered Series

ProdID:

28197

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Laenen, Antonius; Curtis, R. E., Jr.

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ENGLISH

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iv, 15 p. :ill. ;28 cm.

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U.S. Geological Survey,

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Water-Resources Investigations Report

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WRI

Citation Series Number:

89-4090

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Accuracy of acoustic velocity metering systems for measurement of low velocity in open channels; 1989; WRI; 89-4090; Laenen, Antonius; Curtis, R. E., Jr.

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1989

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citation/reference

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Accuracy of acoustic velocity metering systems for measurement of low velocity in open channels; 1989; WRI; 89-4090; Laenen, Antonius; Curtis, R. E., Jr.