The European Space Agency gave the green light on Tuesday to a satellite mission to measure the weight of Earth's forests, helping scientists factor the role of woodlands in the carbon cycle and climate change.

A clash of ecosystems in Bolivia is visible from the Landsat 7 satellite. The tan tones in the lower left of the image reflect an arid landscape in the rain shadow of the Andes Mountains. In the upper right, deep greens represent the frontier of the Amazon rainforest, marked by patterns of deforestation. Credit: Jesse Allen/NASA/USGS
 
The Biomass mission, set for launch in 2020, will pioneer a new type of radar to tally the mass of the world's forests and track their growth and contraction caused by seasons, climate and human activity.

"ESA's made the right decision," said Shaun Quegan, leader of the science team which proposed the mission. "What they've done is both sensible and it's a bit brave in that it's a mission which is unique. It's good for science and it's good for the planet."

The mission will take advantage of a sliver of bandwidth only recently opened up for use by satellites by the International Telecommunications Union, the global regulatory body responsible for allocating radio spectrum.

Biomass will use a P-band radar system with a 39-foot deployable antenna to determine the amount of carbon stored in the world's forests, collecting such data with unprecedented accuracy.

Quegan, a scientist at the University of Sheffield in the United Kingdom, said the P-band instrument works in the longest wavelength possible for a space-based radar.

Unlike more conventional synthetic aperture radars, such as C-band or X-band, the P-band measurements will peer through foliage and detect the core structures of trees containing the bulk of their mass, according to Thuy Le Toan, co-chair of the Biomass proposal team from CESBIO, a French space research center.

"Biomass is effectively the weight of the forest," Quegan said in an interview with Spaceflight Now.

The Biomass mission is the first space mission to utilize the P-band frequencies, bringing both scientific promise and growing pains as managers navigate the realities of policy and diplomacy.

The U.S. military's system of space tracking radars shares the bandwidth to be exploited by the Biomass mission, and the Pentagon is not budging on its insistence the satellite turn off its instrument when in the line-of-sight of its ground-based radar tracking network.

U.S. defense officials fear the Biomass payload will interfere with Space Object Tracking Radars stationed across the United States, Greenland and Britain.

"That wipes out the whole of North America, the Arctic and Europe," Quegan said. "The fact is these consequences are not that serious, otherwise the mission would not have been selected."

According to Quegan, the parts of Earth richest in unrealized biomass discoveries are in the tropics and the forests of China and Siberia. Airborne and ground campaigns have measured the carbon content of forests across North America and Europe for decades, he said.

Quegan said ESA officials will continue negotiating with the U.S. military in hopes of reaching a compromise and opening up at least parts of the restricted areas to Biomass. "I don't think we've heard the final story on this," Quegan said Wednesday.

A sketch of one possible design of the Biomass satellite, which will feature a 39-foot radar reflector. Credit: ESA
 
A board of Earth scientists impaneled by ESA recommended the Biomass mission be selected over proposals looking at atmospheric chemistry and the relationship between snow, water and climate at high latitudes.

Biomass is set to become the seventh mission developed under ESA's Earth Explorers program. Three Earth Explorer satellites are now in orbit mapping Earth's gravity and ocean circulation, studying the planet's polar ice, and measuring soil moisture content.

Three more Earth Explorers will launch in the next three years to focus on Earth's magnetic field, wind patterns and how the planet is shielded from the sun's radiation.

"The Biomass mission is, I believe, a vital one," said Mathew Williams, a professor of ecology at the University of Edinburgh, in a presentation to scientists in March. "It will significantly and uniquely enhance our understanding of the Earth system, and it can also play a major role in supporting our policies in climate and the carbon cycle.

Quegan said Biomass data will be openly shared with researchers, politicians, and the public worldwide.

"Biomass will produce a series of maps globally of forest biomass, forest height, and forest disturbance at a precision, resolution and accuracy that will revolutionize our knowledge of the biosphere, its dynamics, and its interaction with the atmosphere," Williams said. "Specifically, these maps will help to answer an urgent question: What is the role of biomass in the global carbon cycle?"

ESA has set a preliminary limit on the cost of the Biomass mission at 420 million euros, or about $553 million. The space agency says the mission will be confirmed when industrial proposals are received and its cost becomes clearer.

The 2,600-pound spacecraft, to be built by a consortium led by Astrium UK or Thales Alenia Space of Italy, is designed to launch on Europe's lightweight Vega rocket, but it is also compatible with the Russian Soyuz rocket and the Orbital Sciences Antares booster, according to Marco Arcioni, an ESA engineer and technical advisor to the Biomass science team.

The satellite will fly about 400 miles above Earth in a sun-synchronous orbit for its five-year mission.

Quegan said the Biomass mission could also help track compliance with a proposed international treaty to reduce deforestation and promote forest growth. There is currently no reliable way of measuring such activity from country-to-country.

"This mission is for the common good," Quegan said.