Progress report on the ENDECO free-fall CTD (conductivity-temperature-depth sensor system)

A description is given of a vehicle system designed to meet the World Ocean Circulation Experiment (WOCE) specifications and provide a low-cost alternative for the oceanographer to using ships with hydrographic winches and dedicated conductivity-temperature-depth (CTD) systems. The vehicle is tracked using a pressure-coded acoustic pinger synchronized to an IBM-compatible computer aboard the deployment vessel. With horizontal range derived from these measurements, the vessel can maneuver to the pickup site. The system uses a temperature and conductivity sensor designed to allow at-sea calibrations in the triple point of water and gallium standard temperature cells. Water samples are obtained using 12 evacuated pyrex glass 250-ml sample bottles with special break-off fill caps. The round-trip travel time for the free-fall CTD is approximately 1 h to 6500 m compared to 4 h using conventional techniques.<
>