Comparison of current sensors used off an open coast

Simultaneous measurements with two moored current meter arrays and numerous drogues were made at an open ocean site three miles off the New Jersey coast. One current meter array had two ducted propeller sensors and the other two Savonius rotor sensors. The drogues and one each of the two current sensor-types were set six or seven meters above the bottom in twelve meters of water, while the other sensors were one meter above the bottom. Repeated sets of simultaneous measurements were made over a period of one month during the winter through a variety of sea and weather conditions. Correlations among the three methods of current measurements are presented. The degree of agreement between the field observations and both theoretical models and tank tests is also presented. Excessively high velocity measurements obtained using the Savonius rotor are shown to be principally due to rectification of orbital wave motion. The origin of the higher apparent velocities obtained using the ducted rotor is less certain. More definitive results will come from a subsequent investigation in which wave measurements have been made simultaneously. Observations concerning current measurements in the shallow open ocean are discussed.