Because oceanographic research is an expensive endeavor, activity on the research vessel never ceases. Chief scientists always have extensive plans including night operations. A very effective way to maximize the ship time at night is to use a CTD system to track the buoyant plumes of hydrothermal systems in the water column. CTD stands for Conductivity, Temperature and Depth. The sensors on this instrument measure the electrical conductivity of sea water as a way to calculate salinity.
Temperature is measured directly and depth is computed from water pressure.
If scientists search for hydrothermal plumes, a transmissometer is included in the basic sensors to detect particle-rich clouds of vent fluid. The sensors and associated electronics are mounted on a metal frame, which also carries 24 10-liter capacity sampling bottles. This instrument package is lowered from the ship on a cable and towed at depth in the water column to detect any alteration in the temperature and salinity signals that might differ from the ambient ocean water. The sensors operate continuously and provide high-resolution profiles of the properties of the sea water. Concurrently, the sample bottles may be closed individually at different depths to sample water.