Deploying the CTD (Conductivity, Temperature, Depth recorder)
The CTD is an electronic instrument commonly used by oceanographers that continuously records salinity (by measuring conductivity), temperature, and depth (by measuring pressure) as the instrument is lowered on a hydrowire from the ship. The CTD is attached to a frame fitted with a number of large water-collecting bottles called Niskins, the instrument together with the bottles is called the CTD rosette. The Niskin bottles are designed so that they have lids at both ends. They are sent down open, and triggered to close electronically at the depth that water needs to be collected. This way, water can be sampled at many different depths throughout the water column, and kept separate from water collected in other bottles at other depths.