Using small AUV for oceanographic measurements

The use of Florida Atlantic University´s the Ocean Explorer, a small autonomous underwater vehicle, as a mobile platform for oceanographic measurements is described. The OEX is a 2.4 m long versatile, Gertler body which can perform pre-programmed underwater missions to a depth of 300 m. At a speed of 1-2 m/s, it can perform missions over a period of several hours, collecting in-situ oceanographic data and storing it on an on-board data-logger. Three missions are described, two in shallow waters off the coast of South Florida during December, 1997, and one in the Gulf Stream during July 1997 at depths of up to 130 m. During the missions, the AUV was equipped with a 1200 kHz broad band ADCP, a CTD package and, on the Gulf Stream mission, a small-scale turbulence measurement package. The vehicle may also carry a side-scan sonar or other instruments for subsidiary measurements. The versatility of the AUV allows measurement of oceanographic data over a substantial region, the motion of the platform being largely decoupled from that of the sea surface. In the missions of Dec. 5 and 11, 1997, “lawn-mower pattern” AUV surveys were conducted over 1 km2 regions on the east coast of Florida, north of Fort Lauderdale, at a depths of 7 m and 3 m respectively in a water column where depth ranged from 10-32 m. During Dec. 5, the region was subjected to a cold front from the northwest. Local wind measurements show presence of up to 10 m/s winds at temperatures of up to 10-150 C below normal for the, time of the year. Measurements are compared with those of a fixed ADCP. In the Gulf Stream missions, significant shear layers were encountered. Bathymetry, current, CTD and small-scale turbulence measurements obtained during the missions are presented and the problems associated with making such measurements and choosing sampling strategies is discussed