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2002 LAPCOD Meeting
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Surface Wave and Shear Measurements with Surface Drifter
Pierre-Marie Poulain, Davide Deponte and Laura Ursella
Ist. Naz. di Oceanografia e di Geofisica Sperimentale - OGS, Trieste, Italy
ppoulain@ogs.trieste.it(Abstract received 10/25/2002 for session C)
ABSTRACT
CODE surface drifters were equipped with Nortek Aquadopp acoustic velocimeters and with GPS receivers, without changing significantly their hydro-dynamical characteristics (e.g., size, buoyancy and drag area). The velocimeters measured the relative water flow at two levels (~ 30 and 130 cm below the sea surface) near the body of the drifter with an accuracy of about 1 cm/s and with sampling frequency of 1 Hz. The GPS receivers provided high accuracy (~ 1 m) position data at 1 Hz. All the data were recorded on a data logger and memory board inside the drifters. The drifters were operated in Monterey Bay (Eastern North Pacific) in late fall 2000 and in the Northern Adriatic Sea in spring and fall of both 2001 and 2002. The majority of the deployments were conducted in the vicinity of waverider buoys, an oceanographic tower and research vessels from which wave and wind data were collected. Data of the Nortek Aquadopp (relative flow, tilt, pressure) and of the GPS receivers were processed and their high-frequency components were analyzed. Spectral analysis revealed robust surface wave signals similar to those measured by nearby waverider buoys or by bottom pressure gauges (at oceanographic tower). The relative flow data from the top and bottom velocimeters were projected onto the horizontal plane and averaged over 10 min intervals. Vertical shear of the horizontal currents were calculated and projected in the down and across-wind directions. Shears of up to 11 cm/s were found. Regressions of shear versus wind speed indicated that the shear is downwind and to the right of the wind (compatible with Ekman spiral), and that it increases with wind speed.
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2002 LAPCOD Meeting, Key Largo, Florida, December 12-16, 2000