UCTD—A new tool for underway soundspeed profiling

The Underway Conductivity-Temperature-Depth (UCTDtrade) instrument allows the collection of high-quality temperature and conductivity profiles from moving vessels in a cost-effective and environmentally safe manner. From these profiles it is possible to derive other data, such as salinity and sound speed. The system was designed to eliminate some of the disadvantages associated with using expendables and towed vehicles, or stopping the ship to collect CTD profiles without sacrificing data quality. Major design goals were ease-of-use, portability, and re-usability. The system can be used for both open water research applications as well as shallow-water hydrographic surveys. Its principle of operation is the same as for expendable probes, except that the UCTD is recovered after each deployment. Typically, it is possible to profile to over 500 m at a ship speed of 10 kt. At slower ship speeds, profiles to over 1100 m have been obtained. The system can be operated at ship speeds of up to 20 kt. Comparisons of UCTD profiles with data from CTD stations show excellent agreement of the raw data and the derived sound speed profiles. Here, we present an overview of the system components and discuss the performance of the instrument.