First green map of our blue planet
13 February 2006
How's our planet's foliage faring? It's a crucial question for climate scientists - green leaves gobble up the greenhouse gas carbon dioxide. Now new maps are revealing the health of our planet's plants on a global scale.
Antenna investigates...
The maps are colour-coded: reds and purples show plants in prime condition.
Image: Paul Curran
The maps begin life in space, on board Envisat - the European Space Agency's (ESA) state-of-the-art Earth monitoring satellite. Here, a sensor called MERIS measures how much sunlight Earth bounces back into space.
MERIS usually tracks the colour of our watery world's oceans - a good indication of what's going on beneath the waves. But now UK scientists have worked out a way to make MERIS data show just how green Earth really is.
Envisat is the largest Earth monitoring satellite ever built.
Image: ESA
The green blobs in these fresh pondweed cells are chloroplasts. They contain chlorophyll.
Image: Marshall Sundberg, Emporia State University
Greenness is a reliable guide to vegetation's vitality. Plants' green pigment, chlorophyll, is essential for photosynthesis - the sunlight-driven reaction that converts carbon dioxide and water into food. More chlorophyll boosts photosynthesis, which in turn fuels plant growth. |
How does MERIS measure greenness?
Chlorophyll reflects most of the green light that hits it - that's why leaves appear the colour they do. But the pigment also absorbs red light very strongly. Meanwhile, leaves' internal structure bounces back invisible light from the near-infrared end of the spectrum.
MERIS detects how much red and near infrared light reaches its sensors. Linking this info to leaves' chlorophyll content gives a global greenness map.
The MERIS sensor was tested with a 'sun simulator' before being loaded onto the satellite.
Image: ESA
The maps are giving scientists a better idea of plants' carbon dioxide guzzling, so climate-change models can be more accurate. But they also show a more immediate future.
'Our maps can tell us how the seasons are changing: whether spring is coming earlier and what state the vegetation's in.'Paul Curran, mapping expert, University of Bournemouth
Image: FreeFoto.com
Until now, scientists haven't been able to see the big picture on plant health...
'We can learn a lot from smaller-scale studies, but if you want to understand changes and interactions of vegetation and global climate, you have to try to do this on a global scale.'
Mat Disney, environmental monitoring expert, University College London
Mat Disney, environmental monitoring expert, University College London
Mat Disney, environmental monitoring expert, University College London
Who will benefit from the new maps? It's not just scientists...
'Following the Asian tsunami, we used our images to look at how damaging sea water was moving through the soil. Salt water kills plants, but the first telltale sign of trouble is reduced plant growth, which we can pick up.
Paul Curran, mapping expert, Bournemouth University
'Using our maps we could spot affected areas. This information could be used to direct the aid effort to the farmers worst hit.'
Paul Curran, mapping expert, Bournemouth University
Paul Curran, mapping expert, Bournemouth University
Banda Aceh in Indosesia, after the tsunami hit.
Image: DigitalGlobe
With new maps being drawn weekly, there are high hopes for the global greenness pictures.
'We plan to extend our tsunami study to all the other regions affected. We want to see how long it's taking for the plants to recover.'
Jadunandan Dash, mapping expert, University of Southampton
Jadunandan Dash, mapping expert, University of Southampton
Jadunandan Dash, mapping expert, University of Southampton