These are specific measurements of geophysical parameters such as oceanic phytoplankton chlorophyll concentration, cloud-top pressure or terrestrial vegetation cover, to a maximum resolution of 300 metres from 800 km away in space.
Immediately Envisat was launched ESA began a calibration campaign to make sure all instruments, including MERIS, were working optimally. But the processor algorithms applied to MERIS data also needed validation, to see how much they needed 'tuning up' for maximum accuracy.
What this came down to was checking if what the processors reported was really there. Some of this job could be done by cross-checking data with similar spacecraft instruments like CNES's POLDER or NASA's SeaWiFs, but independent verification of ground conditions was also required.
This entailed international efforts to mount a worldwide 'sight test' that ranged from the Greenland ice cap to African deserts, aircraft flights above Europe, buoys in coastal zones and research vessels out in the open ocean.
To ensure overall accuracy all the radiometer instruments used to gather local measurements across the world were first inter-calibrated by the UK Plymouth Marine Laboratory, one of the leading partners in validation efforts.
Checking results on land was the simplest part of the validation campaign, as many cross-comparisons could be done with a European Commission land cover database. Stable desert sit
Contact: Philippe Goryl
European Space Agency