A COMPARISON OF TECHNIQUES FOR REFERENCING GEOSTROPHIC VELOCITIES

A geostrophic velocity section across the Gulf Stream and deep western boundary current near 35-degrees-N is referenced four different ways: using a POGO float (acoustically tracked transport float), shipboard acoustic Doppler current profiler (ADCP), and bottom current meters, a nd by assuming an isotherm level of no motion. The comparison between the first two techniques is emphasized because they are most easily ap plied. In general, reference velocities calculated using the float dat a agree well with those obtained from the ADCP data. However, there is disagreement at locations where the ADCP velocity is not in thermal w ind balance, in which case the POGO value is deemed more accurate beca use the float samples deeper into the subsurface geostrophic flow. Dis agreement is also caused by insufficient cross-stream POGO spacing (al though this could be avoided). The isotherm- and current meter-referen ced sections, while similar to each other, both show unrealistic featu res. It is argued that the POGO method is preferable to the shipboard ADCP for a deep-water hydrographic experiment.