A comparison of simultaneous measurements from shipboard VM-150 and OS-75 acoustic Doppler current profilers

This paper compares the performance of two shipmounted acoustic Doppler current profilers: the well-proven 150 kHz VM-150 instrument and the more recent 75 kHz phased array instrument. On station, mean current profiles over 29-429 m differed by less than 0.2 cm s-' in the east and north components. Mean differences over a 350 km section were larger when underway at - 5 m s -', but no larger than 2 cm s-'. On station, 90% of the profiles from the 75 kHz ADCP achieved a range in excess of 675 m. In calm conditions, the underway range was also in excess of 675 m. However, the range achieved with the instrument decreased faster with increasing wind speed than for the 150 kHz ADCP. During winds of 15 m s-' the range for both instruments lay between 150-300.a