By Jonathan Amos

Science correspondent, BBC News

Jason bounces microwaves off the sea surface to measure ocean height Europe has committed to build the next Jason altimeter spacecraft to monitor the behaviour of the world's oceans. The decision should guarantee the continuation of a remarkable 18-year record of sea-surface shape until late in the decade. It is the Jason series that has traced the recent steady rise in global sea level by about 3mm per year. The data has become invaluable to oceanographers, weather forecasters and climatologists. Eumetsat, which looks after Europe's meteorological satellites, has indicated that its member states will now meet their 25% share of the 252m-euro ($380m; £228m) project. Most of the rest of the mission cost is being borne by the US and France, with the latter providing the spacecraft bus, or chassis, through Thales Alenia Space. Jason-3 should launch in 2013, allowing time to cross-check its data in orbit with the current Jason-2 observatory. Only by flying the pair in tandem for a period of months can scientists minimise calibration errors between the two satellites' datasets. Deep insight Knowing ocean surface elevation has many and varied applications, both short-term and long-term. Just as surface air pressure reveals what the atmosphere is doing up above, so ocean height will betray details about the behaviour of water down below. These measurements are critical to monitoring the effects of climate change and to safe exploitation of the marine environment

Lord Drayson, UK science minister The data gives clues to temperature and salinity. When combined with gravity information, it will also indicate current direction and speed. The oceans store vast amounts of heat from the Sun; and how they move that energy around the globe and interact with the atmosphere are what drive key elements of our weather and the climate system. One of Jason's key roles right now is to monitor the progress of the El Nino phenomenon, which sees an eastward shift in warm water across the central Pacific Ocean. The movement is evident to Jason in an anomalous rise in sea surface height of a metre or more as the changes in temperature make the ocean bulge. El Nino has a profound influence on global weather systems, altering - often quite dramatically - precipitation patterns. Clear trends Although a number of space altimetry missions are now flying, it is Jason that provides the global reference against which all other ocean topography datasets are matched. The concern in the Earth observation community was that the global financial crisis might limit European nations' ability to fund Jason-3. El Nino's warm waters (red) make the ocean surface bulge The EU, the European Space Agency and Eumetsat all have the goal to use space to obtain the "essential climate variables" - to acquire the key pieces of information that reveal the true state of the planet. This requires that satellites gather continuous, cross-calibrated, long-term datasets. With the initiation of Jason-3, there is a good chance that the ocean topography sequence started in 1992 will now be maintained. In addition, agencies have already started discussions about a "Jason Continuity" mission; a Jason-4, in essence. This would probably see an altimeter put on a spacecraft bus similar to the one being used on the forthcoming Cryosat mission. Cryosat is set to launch at the end of this month to gather information about the state of the Earth's ice fields. British support Eumetsat had hoped to make an announcement on Jason-3 after its council meeting in December, but a number of member states indicated that they wanted more time to organise their subscriptions. One of those nations was the UK, which is the second largest contributor to the Eumetsat budget. Scientists hope data from Cryosat will show where Arctic ice is melting fastest Britain has now come forward with a full commitment (based on the relative size of its economy) to the programme over nine years of 10.3m euros (£9m). Most of that money will be fed through the Department for Business, Innovation and Skills. "The UK contribution is vital to the future of the Jason series and the crucial data it provides on sea-surface height across the globe, and we are committed to the Jason-3 satellite," said Science Minister Lord Drayson. "These measurements are critical to monitoring the effects of climate change and to safe exploitation of the marine environment. The government is determined to ensure the programme continues to deliver these to researchers for years to come as we strive to tackle global warming." Only France, as a co-lead nation on Jason, will be putting more into the Eumetsat part of the programme. Jonathan.Amos-INTERNET@bbc.co.uk



Bookmark with: Delicious

Digg

reddit

Facebook

StumbleUpon What are these? E-mail this to a friend Printable version