An advisory panel has recommended that the European Space Agency (ESA) launch a satellite that would measure the faint fluorescent glow of plants, ScienceInsider has learned.
The Fluorescence Explorer, or FLEX, was endorsed as ESA’s next Earth Explorers mission by the agency’s Earth Science Advisory Committee, following a user consultation meeting held last week in Krakow, Poland.
Volker Liebig, the director of ESA’s Earth observation programs, notified the FLEX team of the decision on 18 September, along with team members from CarbonSat, the other mission up for consideration in the Earth Explorer 8 competition. Formal selection of either the FLEX or CarbonSat mission will be made in November by ESA’s Earth Observation Programme Board, but the board has always followed the recommendations of the scientific advisory committee.
The recommendation for the €290 million FLEX mission, which would launch in 2022, is a sign of how plant fluorescence has become one of the most exciting new remote sensing signals for Earth scientists. When light strikes chlorophyll molecules in plants, most of the photons are used in the process of turning carbon dioxide into sugars. But about 1% of them are re-emitted as a faint red glow. FLEX would measure that light, in ground patches as small as 300 meters a side, as a proxy for the efficiency with which the plants are soaking up carbon dioxide.
“The biggest advantage [comes] from the high spatial resolution,” says Christian Frankenberg, a remote sensing scientist on NASA’s Orbiting Carbon Observatory-2 (OCO-2) team at the Jet Propulsion Laboratory in Pasadena, California. “You’re looking at one specific biome and not a mix of different surface properties.”
Launched in 2014, OCO-2 has shown the potential of chlorophyll fluorescence to help Earth scientists understand global fluxes of carbon dioxide in a warming world. But OCO-2 is not a global mapper—it has gaps in ground coverage—and its resolution is limited to about 2 kilometers. By going to 300-meter resolution—closer to the size of fragmented forests and crop fields—FLEX should allow plant physiologists to understand how specific plants respond to different environmental stresses. Another innovation of FLEX is its ability to measure fluorescence associated with two different steps in the photosynthetic system—one in the red and one in the infrared. The red step is suspected to be the better proxy for how efficiently a plant is photosynthesizing under different stresses than the infrared step.
The CarbonSat proposal would also measure chlorophyll fluorescence, but its primary focus, like OCO-2, is the monitoring of carbon dioxide sinks and sources.