During photosynthesis, plants re-emit some of the light they absorb. This faint fluorescence is invisible to the naked eye but detectable by satellites. A team led by Joanna Joiner of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, used new techniques to detangle this weak signal from data collected by the Global Ozone Monitoring Instrument 2 on Metop-A, a European meteorological satellite. The scientists took advantage of the fact that the fluorescence has its own unique spectral signature, akin to a fingerprint, allowing them to tease it out from the rest of the light collected by the satellite.
Previous observations of photosynthetic fluorescence relied on averaging data over areas of 200 square kilometres every month; the new maps average the data over areas of just 50 square kilometres about every ten days. The improved measurements could be used by farmers to spot early indications of crop stress and by ecologists trying to better understand global vegetation and carbon-cycle processes.
‘For the first time, we’re able to globally map changes in fluorescence over the course of a single month,’ Joiner said. ‘This lets us use fluorescence to observe, for example, variation in the length of the growing season.’
The researchers have already observed plants beginning to shut down in the autumn before their leaves began to change colour and clearly detected early plant growth during last year’s warm spring in the USA.
This story was published in the September 2013 edition of Geographical Magazine