Coastal oceanography using a small AUV

Bathymetry, current, temperature, and depth (CTD) measurements using a smal l, mobile, autonomous underwater vehicle (AUV) platform are described. Auto nomous surveys of a shallow water column off the east coast of Florida duri ng December 1997 were carried out using a 2.13-m long, 0.53-m maximum diame ter Ocean Explorer series AUV, equipped with a 1200-kHz acoustic Doppler cu rrent profiler (ADCP) and a CDT package. At a speed of 1-2 m s(-1), this AU V can perform preprogrammed missions over a period of several hours, collec ting in situ oceanographic data and storing it on an onboard datalogger. Th e vehicle may also carry side-scan sonar or a custom small-scale turbulence measurement package or other instruments for subsidiary measurements. The versatility of the AUV allows measurement of oceanographic data over a subs tantial region, the motion of the platform being largely decoupled from tha t of any surface mother ship. In the missions of 5 and 11 December 1997, "lawn mower pattern" AUV surveys were conducted over 1 km(2) regions on the east coast of Florida, north of Fort Lauderdale, at depths of 7 and 3 m, respectively, in a water column w here the depth ranged from 10 to 32 m. During 5 December, the region was su bjected to a cold front from the northwest. Local wind measurements show pr esence of up to 10 m s(-1) winds at temperatures of up to 10 degrees -15 de greesC below normal for the time of the year. The fixed ADCP indicates occu rrence of significant internal wave activity in the region. The data collec ted using the mobile AUV are utilized to develop a map of the bottom topogr aphy and examine current, temperature, and density variations in the contex t of the background information from a fixed bottom-mounted ADCP and Coasta l-Marine Automated Network buoys. The work described here is a significant step in the development of an autonomous oceanographic sampling network, il lustrating the versatility of an AUV platform. The data collected during th e missions described will form part of a bank for information on the impact of a cold front on shallow subtropical waters. The authors expect to repea t the missions during other such fronts.