One of the items we work with at times are Drifter Buoys. This is a scientific instrument that floats at sea and provides scientists all kinds of data of what the seas are doing.
A drifter buoy is made up of three parts. The sphere or floater (about 14 inches in diameter) floats just below the ocean surface. It holds an antenna for sending information to a satellite orbiting above the Earth.
The "holey sock" drogue is attached to it. The drogue usually hangs down about 15 meters. It acts like an underwater sail. When it is pushed by the ocean current, the drogue helps the drifter move with the flow of water. Without a drogue, the buoy would move because of wind and waves, not the current.
The sensors measure ocean conditions, such as the sea surface water temperature. Sensors can also measure wind, ocean color, and other things. The information (data) is measured continuously. Then, an average of the measurements is calculated every hour. The data must be sent to a satellite orbiting the Earth. When a satellite passes overhead (about every six hours), the sets of data are sent to the satellite. The location of the buoy is also sent to the satellite. Then all this information is sent from the satellite to computers at a ground station on land. Scientists read the information from computers and use this information to learn about the ocean.