Old railroad wheels are commonly used as weights, and the floats are hollow glass balls about one-half meter in diameter. At the bottom of each mooring is an acoustic release. We borrowed this idea from marine mammals such as whales and dolphins, which use similar acoustic signals to communicate with each other. We can't use radio or light to communicate because these electromagnetic signals can travel only a short way through water, while sound waves can be heard for great distances. On the moorings we have three kinds of sensors.
Temperature sensors monitor the changing temperature of the seawater.
Optical sensors monitor the amount of particles in the water by shining a light into the water and measuring how much is reflected back from the tiny particles suspended in the water. These particles are created when the hot hydrothermal fluids mix with the cold seawater. Current meters measure both the speed and direction of water movements. By combining all three of these measurements we try and reconstruct the movement of hydrothermal plumes during the time the moorings were on the seafloor. Our first day of mooring work has been highly successful.