Airbus Defence and Space

Some scientists believe – although the theory remains hotly debated – that much of the water in the oceans arrived on Earth from space, delivered in comets over four billion years ago. So it is perhaps appropriate that the science of oceanography has been revolutionised by space-based technology.

In 1769, Benjamin Franklin, future US president, and his cousin and collaborator Timothy Folger produced the first map of the Gulf Stream, the current that carries warm water from the coast of Florida to Europe.

Over the following several hundred years, scientists crisscrossed the world’s oceans collecting data to explain how water moved around the planet. It was – and still is – hard and slow work: an area of 361,000,000 square kilometres – about 72% of the Earth’s surface – is covered by ocean. Then, in 1992, a revolution in oceanography took place: the TOPEX/Poseidon satellite was launched, the first spacecraft launched to study ocean-surface topography. A joint mission between NASA and CNES, the French space agency, TOPEX/Poseidon can be said to have completely changed the way we understand the bodies that hold nearly 97% of the Earth’s water.

TOPEX/Poseidon was so revolutionary because for the first time oceanographers could have almost real-time readings from vast areas of the sea, in contrast to the small scale and slow pace of in-situ sea-based operations. From its orbit 1,330 kilometres above the Earth, the satellite used a radar altimeter to measure the height of the oceans to an accuracy of 3.3 centimetres and produced the first-ever global maps of sea height.

Perhaps its most important contribution to oceanography, however, was to finally provide data on the ocean’s ‘conveyor belt’, the movement of water that takes cold, more saline water from the Arctic down the through the Atlantic, across the Indian Ocean, into the Pacific Ocean, and back again. This has allowed scientists to better understand how the heat from the sun is stored in the ocean, how the waters in the oceans mix and to track how climate change may be altering the way the belt functions.

In the past 10 years, over 30 new satellites have been launched to study the world’s oceans, measuring variables including its colour (which reveals levels of carbon dioxide-‘eating’ phytoplankton), temperature, as well as other more specific missions such as ones looking at the most endangered coral reefs, the winds over the oceans and fish-stock movements. (The latest is SMOS, launched in November 2009 to measure soil moisture and ocean salinity.)