Horizontal Response of the NBIS Acoustic Current Meter

The Neil Brown Instrument System Acoustic Current Meter (ACM) is one of the most advanced current meters available. This meter is an excellent instrument for research purposes, but is limited by its horizontal response. This paper concerns the errors due to non-cosine response in the horizontal plane. By towing the NBIS ACM at known speeds at various angles to the direction of tow, the responses of both axes of the current meter were determined. Calibration runs were performed on three current meters at a nominal speed of 10 cm/s and on one current meter at 12 cm/s and 31 cm/s. The error induced by the wakes of the supporting rods can reach ± 8% of the flow speed. By using a least squares Fourier series to correct the out puts, the error may be reduced to 1 - 2%.