European Space Agency

	Fig1: Envisat ASAR mosaic of the Arctic Ocean for early September 2007, clearly showing the most direct route of the Northwest Passage open (orange line) and the Northeast passage only partially blocked (blue line).The dark grey colour represents the ice-free areas, while green represents areas with sea ice

The 25 billion tons of carbon dioxide pumped annually into the Earth’s atmosphere by human activity are contributing to global warming. Warming seas and melting glaciers are estimated to be raising mean global sea level by 2-3 millimetres each year, increasing the risk of severe flooding for low-lying coastal cities in Europe, Asia and Africa. Mountain glaciers, which used to provide a reliable summertime water source for much of the world’s agriculture, are gradually disappearing. Melting sea ice (Fig 1) will open up global transportation shortcuts via new arctic sea routes and allow exploitation of previously inaccessible oil reserves. However, such benefits need to be weighed against the negative impacts, and whatever the outcome of that debate, no one can reasonably argue against the need for careful management of the changes we are bringing upon the Earth system. Effective management starts with quantitative, accurate and unequivocal information on the state of the planet. ESA’s GlobColour and GlobCarbon projects address part of this information requirement by providing scientists with valuable multi-satellite datasets on biological activity on land and sea.

The GlobColour Project

The colour of oceanic seawater depends largely on the number of microscopic phytoplankton it contains. Clear blue surface waters in the middle of ocean basins are poor in nutrients and contain relatively few phytoplankton, while regions of up-welling near continental shelves bring nutrient rich waters from the deep ocean to the surface, enabling phytoplankton to bloom and adding a green colour to the water.

Tiny phytoplankton are the first link in a food chain which continues up to the fish we like to eat. The ocean’s biological activity is worth watching for more reasons than its fundamental role in food supply. It acts to mitigate climate change by absorbing carbon from the atmosphere, and turning some of it into organic detritus, which eventually sinks to become locked in sediments on the deep sea floor. This is the ocean biological pump, which reabsorbs some of the carbon yearly emitted into the atmosphere.

Some carbon dioxide also dissolves into the oceans. Together these two processes are estimated to be equivalent to the terrestrial carbon sink. However, dissolved carbon dioxide may cause a gradually increasing acidification of the oceans which could eventually reduce the ability of coral and some types of plankton to build their skeletons and shells. This could cause a reduction in biological activity and the amount of carbon absorbed by the oceans. Monitoring the evolution of the biological pump as atmospheric carbon dioxide increases is therefore essential for accurate projections of future climate change. This sensitivity means information on ocean biology is also a useful indicator of climate change. It can help scientists to check the predictions of their highly complex models, and to give them early warning of unexpected changes.

	Fig 2: A GlobColour chlorophyll product showing the distribution of phytoplankton in the Atlantic Ocean, visualised using Google Earth

The three-year GlobColour project kicked off in 2005 under the joint leadership of ACRI in France and the University of Plymouth in the United Kingdom. The objective is to produce the best possible global daily ocean colour data set by merging data from the three most capable sensors: SeaWiFS, MODIS on Aqua, and ENVISAT’s MERIS, and to process all available data from them to produce a consistently calibrated time series from 1997 to 2008.

The data are freely available for use by the worldwide science community via the project’s web portal: www.globcolour.info.

The GlobCarbon Project

Our current knowledge of spatial and temporal patterns of carbon pools and fluxes is uncertain, particularly over land. Recent intercomparisons have shown that with best predictive vegetation models, such as the Lund-Potsdam_Jena (LPJ) model, there is general agreement on global carbon balance but disagreement on how the carbon is distributed. Further progress in understanding of the global carbon cycle and its likely future evolution depends, in particular, on improved observations of the terrestrial carbon processes to narrow the large uncertainties in the magnitudes and locations of carbon fluxes between the land, oceans and the atmosphere. However, this requires a holistic approach combining models, observations and process studies, and not just focusing on the terrestrial component, but coupling it with the atmospheric and oceanic measurements as advocated by the Integrated Global Observing Strategy Partnership (IGOS-P) Carbon Theme Team.

The ESA GlobCarbon project was initiated to aid this process by generating fully calibrated estimates. The GlobCarbon Initiative features estimates of global burned area, the fraction of absorbed photosynthetically active radiation, leaf area index and Vegetation Growth Cycle for ten complete years, from 1998 to 2007. The baseline inputs are 1km satellite sensor data from sensors on the second ESA European Remote Sensing (ERS-2) and ENVISAT satellites and from the fourth and fifth Système Pour l’Observation de la Terre (SPOT) satellites.

The five-year project kicked off in 2003 under the joint leadership of VITO (Belgium) and IGBP (Sweden). The total throughput and product handling required to produce the GLOBCARBON outputs amounts to approximately 50Tb from four sensors (ATSR-2, VEGETATION,AATSR and MERIS). The data are freely available for use by the worldwide science community via the project’s web portal: www.globcarbon.info.

	Fig 3: ESA’s upcoming Sentinel-3 operational mission, scheduled to be launched in 2012

Future

ESA’s Sentinel-3 will carry the Ocean and Land Colour Instrument (OLCI), based on MERIS, and the Sea and Land Surface Temperature (SLST) instrument, derived from the ATSR series. OLCI and SLST will have significantly enhanced capabilities to provide more accurate retrieval of both land and ocean biophysical properties. For example OLCI is designed to allow measurement of chlorophyll not only in the open ocean, but also in coastal waters, by providing operational monitoring of other optically active marine components such as dissolved organic material and suspended sediments. These two instruments will provide the necessary long-term series to better understand global change.

With operational satellite missions in place for another 20 years, the merging of the output datasets also needs to be considered in an operational context, by the development of comprehensive calibration and validation schemes.

Through GlobColour and GlobCarbon, ESA is currently providing scientists with the best possible ocean colour and land information data set for carbon cycle research. This will allow politicians to make informed decisions concerning climate change mitigation and adaptation policy. To reinforce this process the initial GlobCarbon and GlobColour time series will need to be extended well into the future to allow scientists to continue to monitor and more fully understand the role of the sea and land in the carbon cycle.

W: www.esa.int