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Until recently it was impossible to carry out large-scale measurements of photochemical activity in the tropical rainforest and therefore draw conclusions on the subject. A chance success – a measurement by a satellite over the Brazilian Amazon – represents a scientific breakthrough. The technology used shows the effects of drought, heat or cold on plants, which is very useful when analysing agricultural production or climatic conditions. University of Twente scientists and NASA researchers have published an article on the research in the journal Proceedings of the Royal Society B.

For many years now scientists have been using satellites in earth's orbit, but this is the first time that measurements of this particular kind have been successful. Christiaan van der Tol, a researcher at ITC (the Faculty of Geo-Information Science and Earth Observation), is very excited about the discovery. "This is a fantastic stroke of luck on the part of Japan's GOSAT (Greenhouse gases Observing SATellite), which has been orbiting the earth since 2009. In fact it is not the only satellite orbiting there: there is heavy satellite traffic around the earth, both working and non-working satellites. "GOSAT is actually designed to measure greenhouse gases in the atmosphere." But the satellite turned out to be sufficiently precise and sensitive to another very weak signal, the red-coloured light that indicates plant growth.

During photosynthesis, the process whereby a plant uses sunlight for growth, it radiates a tiny amount of red-coloured light. The satellite was able to distinguish this weak signal from the reflected sunlight. The red light, also known as fluorescence, enables plant biological activity to be observed from a great distance. The measurements showed, for example, that while the tropical rainforest remains green during dry and sunny periods it grows less fast than in wet periods.

GOSAT, which was not designed to carry out measurements of this kind, picked up the plant growth signal, although the technology has been known for some time now. The ESA (European Space Agency) is investigating the possibility of a dedicated satellite.