Scientists from Bournemouth University and the University of Southampton have devised a new method of examining how much of the earth's surface is covered by vegetation and assessing the state of health of the foliage.

The European Space Agency (ESA) has recognised the value of this information which is likely to be a vital tool for researchers examining models of terrestrial productivity, gas exchange and climate change.

Dr Jadunandan Dash from the School of Geography and Visiting Professor Paul Curran of Bournemouth University use data from an instrument called Medium Resolution Imaging Spectrometer (MERIS) on board the world's largest environmental satellite, Envisat. It measures reflected radiation in visible red and near-infra red wavelengths. This information, in turn, is used in a tool called the MERIS Terrestrial Chlorophyll Index (MTCI), which has been an ESA operational product since 2004.

"This product enables us to hold a mirror up to our planet and observe, on a regular basis, just how healthy it really is," said Professor Paul Curran. Images taken in March and August clearly show differences in chlorophyll content between the northern and southern hemispheres. In both maps, the tropical rainforests had relatively high MTCI levels, but even in the centre of these forests there is a change in values between March and August.