Space: Biomass, a satellite to observe the hidden side of tropical forests

It's a spatial eye that will scrutinize the green lungs of our planet. The Biomass scientific satellite launched this Tuesday, April 29, from the Kourou Space Center in French Guiana. Aboard a Vega C rocket, the European satellite will enter orbit at an altitude of 666 kilometers. Its mission: to map, with unprecedented precision, the biomass of tropical forests—that is, the total quantity of organic plant matter—to measure the amount of carbon they can absorb.

Forests play a key role in the carbon cycle: through photosynthesis, they capture a significant portion of atmospheric carbon dioxide and store it in their biomass and soils. They alone retain approximately 70% of the carbon contained in terrestrial ecosystems. Tropical rainforests, in particular, contain nearly 50% of the carbon in the world's vegetation. Carbon dioxide, or CO2, is thought to be responsible for 65% of the additional human-caused greenhouse effect.

However, these natural sinks are vulnerable. Under the influence of natural disturbances (drought, fires, pest attacks) or human activities (deforestation, soil degradation), they can massively release this carbon into the atmosphere, thus reversing their beneficial role.

Currently, the method for measuring forest biomass relies on extrapolations from field plots and satellite images that are inadequate for the density of tropical forests. This makes it impossible to reliably determine whether a given tropical forest region is a carbon sink or source—or how this situation changes over time.

"We are trying to limit the uncertainties we have about their storage capacity, which are currently around 20% to 25%," explained Dominique Gilliéron, head of the European Space Agency 's Earth Observation Projects Department, during a press conference. This is precisely the task that Biomass will be working on for five years.

To successfully measure the carbon absorption capacity of tropical forests, the European satellite is carrying pioneering technology: a synthetic aperture radar (SAR) operating on the P band, an extremely low frequency (70 cm wavelength). This unique capability allows it to penetrate deep into the canopy, up to 40 meters below the plant cover. While conventional optical sensors and radars fail in the face of the thickness of tropical forests, Biomass will be able to reach the internal structures, where the majority of biomass—and therefore carbon—is concentrated.

To go even further, Biomass combines three cutting-edge techniques: polarimetry, interferometry, and radar tomography. Using these methods, it will be able to monitor ecosystem changes with great precision: plant growth, losses due to fires, deforestation, natural regeneration, or changes in land use (such as deforestation).

Beyond forests, the satellite will also provide unprecedented information on other environments such as ice caps , deserts and the topography beneath the canopies. But it is in understanding the role of forests in global warming that its contribution promises to be decisive.

Since the 2015 Paris Agreement , countries have committed to achieving carbon neutrality, a delicate balance between human-caused greenhouse gas emissions and their natural absorption by carbon sinks such as forests and oceans . But developing effective climate policies requires precise knowledge of carbon flows through ecosystems. By better quantifying carbon sinks and the effects of their degradation, Biomass is an essential data source for climate modeling, monitoring environmental commitments, and planning climate change mitigation measures.