article: Known as Flex, the mission was approved by member states on Thursday and will likely launch by 2022. The satellite will carry a spectrometer to catch the subtle but telltale fluorescence that organisms produce when they engage in photosynthesis. Scientists say this signal can be used to monitor the condition of croplands and forests. Changes in the light emission, which is detected in the red and far-red part of the electromagnetic spectrum, will reveal, for example, if vegetation is being stressed, perhaps because of overheating, drought or disease. Given the fundamental role played by photosynthesis in biology, there is arguably no measurement more significant than the one Flex is going to try to capture from orbit. "We will be monitoring the core of the most important process that sustains all life on Earth," said Uwe Rascher, a leading figure on the mission science team. Flex is the latest concept in Esa's Earth Explorer series. These are satellites that are designed to health-check the environment using novel instrument technologies. Missions already flown have mapped Arctic sea-ice, traced ocean circulation, and quantified the amount of water bound up in soils. Flex (Fluorescence Explorer) (PDF) was green-lit as the eighth spacecraft in the series by the agency's Earth Observation Programme Board, meeting in Paris. It won approval following a detailed assessment by scientists and engineers, who put it ahead of a rival proposal called CarbonSat (PDF). This would have plotted the movements of carbon dioxide and methane through the atmosphere. Although a loser on this occasion, CarbonSat may yet find support in a European Union-funded space programme. Certainly, Esa officials would like to continue technology developments on its instrument to try to mature its design. Plant fluorescence has been detected from orbit before, but not at the level of detail envisaged for Flex. Leaf photosynthesis – the production of life-sustaining sugars from CO2 and water – dumps some of the energy not required in the biochemical process in the form of light. This "waste emission" radiates from the vegetation around a couple of peaks in wavelength between 640 and 800 nanometres – on the boundary between the visible and the infrared. The nature of this signal describes directly the efficiency of the photosynthetic process, and if Flex can characterise it accurately it will be able to discern the physical condition of plants. "If you have water-limitation in agriculture – at the moment, we can only see it late, when the vegetation starts to wilt: when it gets brownish, yellowish and begins to drop leaves," explained Prof Rascher. "With a fluorescence signal we see the limitation of photosynthesis because of water stress immediately when it occurs. So, we see the signal before the plant shows visible damage," the Jülich Research Centre scientist told BBC News. The technique does require some ancillary data - in particular, a measure of the temperature of the vegetation being studied. To get this information, Flex would fly in close formation with another satellite already dedicated to the purpose. This would be the EU's Sentinel-3 platform, which will soon start mapping the
summary: The European Space Agency is going to build a spacecraft to map the red glow emitted by Earth's plants.