Autonomous Gliders

On of the most modern oceanographic instrument is the autonomous glider. Gliders are autonomously diving and moving platforms for measurements sensors. During their several months long deployments they are able to move up to 3000km through the oceans. They move in characteristic zig-zag pattern and continuously measure physical and biogeochemical parameters such as temperature, salinity or oxygen and chlorophyll content.

This animation shows the typical movement pattern of an autonomous glider.

 

 

Glider Principle

Autonomous gliders are a logical improvement upon another oceanographic instrument developed in the 1990s, the float. Floats consist of a pressure resistant cylinder, a small internal data recording computer and, in their simplest configuration, sensors for temperature and salinity. With an integrated high pressure pump they are able to move oil from a container inside of the pressure cylinder into an external rubber bladder and back. This movement of oil changes the volume of the float while its weight remains the same. Together this constitutes a change in density. If correctly adjusted a float can change its density from being higher than the surrounding water to being lower. The result is a sinking or rising of the float in the water. Within the international project ARGO some 3500 floats are currently populating the world's oceans and continuously monitor temperature and salinity at depths up to 2000m.

What if one could steer these floats? This is the basic idea behind autonomous gliders. Gliders are very similar to floats but additionally possess two small wings and a compass. Similarly to floats they can modify their volume and sink and rise in the water column. During the down- and upward movements the little wings create a force propelling the gliders forward. Their speed is limited to about half that of a pedestrian and the for every meter down or up they make two to three meters forward. The direction of this forward movement is controlled with the help of an airplane-like rudder at the tail of the glider. Once the glider reaches the ocean surface an internal battery is shifted so that the antennas in the tail get better contact to satellite navigation and communication systems. The glider then connects to a land station and transmits the data collected in the preceding hours. At the same time the new waypoints can be transmitted to the glider.

Further information on GEOMAR's currently active gliders can be found at: GEOMAR Gliderweb.