Inverted echo sounders measure changes in the time it takes a sound pulse to travel from the sea floor to the sea surface and return. Changes in the travel time are related to changes in density of the overlying water, which are in turn related to changes in ocean currents. Sea floor electrometers measure the average speed of an ocean current by sensing the electric field created by salty seawater moving through the Earth's magnetic field. Satellites are an invaluable tool for oceanographers because they can provide regular observations of the entire globe. The satellite instrument of most importance to oceanographers is the altimeter.
Satellite altimeters measure the height of the sea surface with an accuracy of a few centimetres.
The ocean models are combined with models of the atmosphere and sea-ice to create comprehensive models of the global climate system that can predict how climate may change in the future. For these climate predictions to be reliable, ocean currents must be accurately reproduced. Understanding the circulation of the Southern Ocean and its interaction with the atmosphere and sea-ice lies at the heart of reliable predictions of climate change. The Australian Foundation for Science and the Science and Technology Awareness Program of the Commonwealth Department of Industry, Science and Resources are also supporters of Nova . This topic is sponsored by the Cooperative Research Centre for Antarctica and the Southern Ocean and the Commonwealth Department of Industry, Science and Resources .