Satellites offer a frequent overview of our entire planet – covered mostly by water – and provide valuable data to monitor and understand global ocean circulation. Understanding water currents at the ocean surface is important for many applications.
Ocean surface currents have long fascinated oceanographers as they work to understand the role of oceans in the Earth system and how they affect our climate. Measurements of ocean surface currents are fundamental to a number of practical applications, such as marine search and rescue and emergency response, ship routing, anthropogenic and natural pollution and offshore renewable energy monitoring.
Ocean currents are complex and highly dynamic, and therefore need to be monitored constantly on a global scale.
Satellites provide a wide range of data that can be used to generate surface ocean current maps at different time and space scales depending on the techniques used.
Radar altimetry measures sea-surface topography, and is used to derive estimates of geostrophic currents over a period of about 10 days. New Doppler techniques using synthetic aperture radar measurements can measure surface currents.
ESA’s Earth Explorer satellites, CryoSat, GOCE and SMOS, are helping to provide ocean measurements. The upcoming Sentinel family of satellites under Europe’s Global Monitoring for Environment and Security (GMES) programme will also contribute once operational.
To improve the accuracy and to validate estimates of ocean currents from ocean models, it is important to combine satellite observations with in situ data sources provided by drifting buoys and ships.
“As is now the case with space surveillance and tracking, satellite observations can offer homogeneous, gridded data while the in situ observations allow for validation and calibration,” said Rick Lumpkin, oceanographer at the National Oceanic and Atmospheric Administration in the US.
“Furthermore, the satellite observations can be used to identify bad in situ data, improving their value for ocean and climate studies.”
At the ESA GlobCurrent User Consultation meeting held in March in Brest, France, international users met with Earth observation experts to discuss requirements for improved ocean surface current data products.
“What we need is the best ocean current data twice per day globally and to have confidence in the quality of the products so that we can get our ships to the right place at the right time in the most economical way,” said Michel Cochennec at the Fleet Navigation Center of CMA Ships.
For ship routing applications, small savings in fuel by better use of surface currents is a real challenge – but one that could lead to saving tens of millions of Euros per year.
“Ocean surface currents are extremely important to our operations and we can provide two reports per day from our fleet of over 400 ships to help validate satellite data.”
As the oceans transport energy from the tropics to the polar regions, accurate knowledge of ocean surface currents is essential for accurately predicting how our planet will react to a changing climate.
“By synthesising satellite observations, GlobCurrent will provide the complete picture of the ocean’s surface circulation that is urgently required by the scientific and maritime communities to meet the environmental challenges facing society in the 21st century,” said Dr Rory Bingham of Newcastle University in the UK.
The conclusions and requirements that emerged from the meeting are now being used to define the scope for a potential ESA-funded GlobCurrent project under the Data User Element programme.
GlobCurent aims to develop improved ocean surface current products based on the innovative use of Earth observation satellite and in situ data linked to external user applications.
