Each bottle has two caps, one on the bottom and one on the top allowing water to freely flow through as the package is drawn through the ocean. A single bottle may can be closed at any time with a click of a mouse to draw a water sample. The CTD itself is mounted on the metal frame below the collection of bottles. This instrument measures the electrical conductivity of the sea water to calculate its salinity. Salinity is then used as an indicator of the density of the sea water which normally increases with depth.
Temperature is measured directly and normally decreases with depth.
Depth is related to water pressure. While searching for hydrothermal vents the operator carefully watches the temperature and density readings for anomalies. Finally, the package also contains an acoustic transponder which emits and receives sound signals for accurate location and instruments for measuring turbidity and dissolved oxygen. Their surveys pointed to two sites of interest along the Ridge to the north of the Salty Dawg field. Those sites are currently under investigation.