Performance of the nortek Aquadopp Z-Cell Profiler on a NOAA surface buoy

Observations of current velocity in near-surface and near-bottom boundary layers are critically important for many scientific, operational, and engineering applications. Nortek developed the Aquadopp Z-Cell Profiler, a dual-frequency, six-beam acoustic Doppler current profiler, to meet the needs of observing the complete water column velocity profile, including the near-surface or near-bottom currents. The Aquadopp Z-Cell Profiler employs three acoustic beams directed horizontally and spaced equally around the circumference of the profiler with 120 deg spacing between the beams. These beams measure the two-component horizontal currents at the level of the instrument (cell zero), thereby eliminating the common blanking distance associated with standard ADCP's. Near-surface and water column current velocity profile observations from a Z-Cell Profiler mounted on a NOAA NDBC 3 m discus buoy (located in the northern Gulf of Mexico) are compared with current velocity profile measurements from a bottom mounted 600 kHz Nortek AWAC and 600 kHz Teledyne RD Instruments Workhorse acoustic Doppler current profiler. A tidal analysis suggests that velocity data from the horizontal beams (cell zero) are of good quality and consistent in direction and magnitude with the velocity measurements in cells below, with the AWAC and Workhorse velocity, and with theory. Several cases are presented that indicate the measurements in cell zero are important to make independent of velocity lower in the water column in order to correctly characterize the flow regime. Current speed and direction differences between cell zero and lower cells project a horizontal spatial separation of water parcels as much as 20 km/day, with a mean separation of 8.5 km/day.