Forest-Measuring Orbiter Picked for Future European Earth Science Mission

Reflecting success. The planned Biomass spacecraft would use a 20-meter-wide deployable radar reflector to track tree growth.

European Space Agency

It looks fairly certain that Europe's next Earth-observing science mission to win approval for construction will be Biomass, a spacecraft that will be able to measure the carbon content of the world's forests with unprecedented range and accuracy. Biomass was one of three candidate missions that the European Space Agency's (ESA's) Earth Science Advisory Committee studied during a workshop in Graz, Austria, last month. Volker Liebig, head of ESA's earth observation program, tells ScienceInsider that following the meeting, the committee picked the €420 million Biomass to go forward.

The final decision rests with ESA's Earth Observation Programme Board, made up of representatives from ESA's 20 member states, which will meet in early May. It's customary for ESA program boards to accept the recommendations of their advisers. "I've never seen a closer decision" than the one in Graz, Liebig says. "They were all very good." Shaun Quegan, chair of the Biomass mission advisory group, says it was "a very high stress meeting. We had 3 days of questioning. It's taken me 2 weeks to recover." The other two shortlisted missions—which had been whittled down from an original list of over 20 possibilities—were CoReH2O, which sought to model the water balance in glaciers and snow-covered areas, and PREMIER, which aimed to study chemical processes in the upper troposphere and lower stratosphere and the radiative effects of clouds. Both can reapply for future opportunities.

Biomass is a radar mission which will bounce radio waves off the forest canopy to learn about the amount of material present and the height of the forest. It will use 70-centimeter radio waves, the longest you can use from space without getting tangled in the ionosphere. Until recently, such radio waves, known as P-band, were reserved for other uses and so were out of bounds for research satellites. Scientists could carry out studies from aircraft, but they don't provide the same global coverage as a satellite. In 2004, the rules governing P-band were relaxed, and the Biomass team proposed the mission to ESA in 2005. The Biomass radar will still have to be turned off when it is over North America and Europe because it will interfere with systems used by the military to track objects in space, but forests there are relatively well studied; it's the swathes of forest in the tropics, Siberia, and China that will be the new satellite's main concern.

Radio waves at different polarizations bounce off different parts of the forest canopy and soil. By measuring the power and phase of the reflected polarized beams, Biomass can derive the weight of the wood in the forest. If it later scans the same area from a parallel track, it can perform a technique called polarimetric interferometry to calculate the height of the forest. With more passes, researchers can perform a technique called tomography, which can characterize the material in different layers of the forest cover. "We will map the biomass of all the world's forests," Quegan says.

Alongside burning fossil fuels, land-use change is a major source of carbon dioxide escaping into the atmosphere. The Biomass mission will be able to study the loss of carbon through the degradation of forests and deforestation, as well as study the effectiveness of reforestation. "It changes the game completely," Quegan says. "We'll be able to see things we've never seen before."