presence of aerosols and also water vapour concentration up to an accuracy of 3%, which represents unprecedented accuracy.
"Water vapour is highly variable in the atmosphere, and knowledge of its distribution would be very useful for forecasting rainfall. MERIS's revisit time of three days is too low for operational weather forecasting, but it raises the suggestion that a version of the instrument might be flown on future weather satellites."
Over solid ground, MERIS images provide information on land use and vegetation cover, and specific chlorophyll-linked spectral bands help quantify biomass concentration and condition.
Professor Jose Moreno of the University of Valencia detailed MERIS-related results from a July multi-spacecraft validation campaign carried out at the Barrax test site in La Mancha, Spain. The agricultural fields making up the site were characterised to a very high degree of detail, with more than 4000 ground samples taken, plus recordings of atmospheric conditions.
"Often you can have a good knowledge of the land surface corrections required but not the atmospheric corrections - or vice versa," said Moreno. "But with MERIS we have both, which means we can be more confident the data show what is really there.
"Being able to compare MERIS data with ESA's Proba micro-satellite was also useful. The main camera on Proba has four times the spectral bands on MERIS, and its resolution is 30 metres instead of 300 metres – so we could make out individual fields with Proba, to check them against what the larger-scale MERIS images were showing."
Since MERIS products became available in March 2003, Dr Cristina Rodríguez-Benito of Chile-based oceanographic company Mariscope Chilena has been using it to chart one very specific phenomenon: fish-killing algae blooms that threaten Chile's successful aquaculture industry.
"My interest is not only scientific research but also to focus this work on a direct application," said Rodríguez-Benito. "MERIS works better for the purpose of detecting algae blooms than comparable ocean colour instruments such as MODIS."
Formed from individually microscopic phytoplankton, algae blooms occur when favourable local conditions encourage their growth to 'bloom' out of control. Some algae species contain toxins that can poison humans who eat contaminated shellfish. Alternatively the spreading blooms can deplete water of oxygen as they decay, causing larger fish to suffocate.
Fish farms are especially vulnerable to algae blooms because fish cannot flee affected zones. The southern region of Chile has 360 fish farms in the ocean and 40 in freshwater, producing up to 450,000 tonnes of biomass annually. In 1997 alone, Chilean algae blooms caused losses totalling €10 million ($12 million).
Rodríguez-Benito's pilot project – recounted during the Workshop - is co-funded by Mariscope Chilena and Salmon Chile, the national fish-farming industry association. These institutions aim to investigate the feasibility of an operational satellite-based early warning service.
"As spring came to the southern hemisphere in October we have witnessed new blooms appearing," said Rodríguez-Benito. "In situ water testing, using an instrument called a Fluoroprobe, confirms the detection of five different algae classes. The total chlorophyll concentration measured using this fluorometer was successfully correlated with MERIS data."
"The project will continue until the beginning of 2004, as a first step. For the near future we also hope to make use of other Envisat instruments to simultaneously measure important variables like sea surface temperature and ocean currents. Knowing these will be necessary to make forecasting the drift of algae blooms a reality."
In concluding the Workshop on Thursday afternoon, Peter Regner thanked all participants for the very high quality contributions they made: "The Workshop discussions brought forth a number of valuable recommendations which will certainly be taken into consideration in the definition of the future MERIS exploitation plan."
He indicated that the next opportunity for