At 5:15 a.m. EDT an Arianespace Vega C rocket launched a European Space Agency (ESA) satellite mission aimed at measuring the biomass of Earth’s forests. Appropriately called “Biomass,” the mission will be using a unique type of synthetic aperture radar (SAR) to perform the survey, one that has never previously been deployed on a satellite.
The Biomass mission
The “Biomass” mission, according to the ESA, is “designed to deliver crucial information about the state of our forests and how they are changing, and to further our knowledge of the role forests play in the carbon cycle.”
As they note in their introduction to Biomass, Earth’s forests play a critical role in absorbing atmospheric carbon dioxide, removing “around 8 billion tonnes (net) of carbon dioxide from the atmosphere each year.” Losing them could have a catastrophic impact on Earth’s climate and on human civilization.
At the same time, however, scientists and policymakers still don’t know how much carbon is actually stored in those forests. They also don’t know how it’s changing over time, and what factors might be causing those changes. Could temperature change be a factor, or deforestation, or the very anthropogenic carbon dioxide in the atmosphere that’s causing climate change in the first place?
Quantifying and measuring all of this is “essential,” according to ESA, and so the mission will begin to build that dataset.
It is the seventh of ESA’s “Earth Explorer” missions, intended to “address key scientific challenges identified by the EO (Earth Observation) community,” and are each dedicated to “observing a different aspect of Earth’s system”: including the Cryosphere, Hydrosphere, Atmosphere and Ionosphere among others. Current missions include CryoSat, EarthCARE, SMOS and Swarm. The mission was originally intended to start in 2020, but has been delayed until now.
P-band radar “slicing” through the forest cover
ESA acknowledges that this is a “huge technical challenge.” They said that “forests are complex structures and different tree species and dense canopies make them difficult to measure from space.” Optical satellite imagery would have a difficult time peering through the canopy, and even other radar-based solutions would be inadequate.
To address this issue, ESA’s new satellite will be using P-band SAR — longer-wavelength radar with a frequency range between 225 and 390 MHz — which can see through cloud cover and “slice” through the whole forest layer. ESA explained that the signal will be scattered back to the satellite “according to the individual elements of the forest,” which will carry information about the forest’s structure that can be used to “infer forest biomass and forest height.”
This will, they hope, “lead to better insight into rates of habitat loss and, hence, the impact this may be having on biodiversity in the forest environment.” The radar can also be used to map deserts’ subsurface geology, the structure of ice sheets, and “the topography of forest floors.”
NASA used P-band SAR on their AirMOSS radar mission in order to collect rootzone soil mosture. The AirMOSS radar was deployed on a Gulfstream business jet, however; this will be the first satellite carrying this kind of radar system.
Biomass creating “novel” forest maps
The radar instrument’s power amplifier subsystem actually “includes two identical assemblies,” according to ESA; one for vertical polarization, and one for horizontal. These two assemblies alternate, each creating and sending radar pulses to earth in turn through the satellite’s large 12-metre reflector. After returning, the received signals are amplified, digitised, and stored onboard the satellite, to be eventually used create the 3D maps of the forests.
The mission of the satellite is “operated in two phases” according to ESA: the “tomographic phase” and the “interferometric phase.” The first one will create 3D maps of forests, which ESA said was “novel to Earth observation.” The second phase, they said, “allows forest height and above-ground biomass to be estimated.” They expect to acquire “around five global maps” using the satellite.
The satellite will orbit in a sun-synchronous dawn-dusk orbit at an altitude of 666 km. ESA said that the satellite’s left-looking SAR will “cover a single fifty- to sixty-kilometre swath at a time.” Biomass was, according to ESA, “developed by over 50 companies led by Airbus UK.”
The launch itself happened from Europe’s Spaceport in French Guiana on early Tuesday morning. According to Arianespace’s release on the VV26 mission, the Biomass satellite is the rocket’s sole payload on this mission. Nine days after being carried to space and separating from the Vega-C — an “exceptional” amount of time according to ESA — they will begin “bringing the spacecraft to life”: checking the subsystems and activating the ground segment.
After that will begin the “careful deployment” of the satellite’s large stowed reflector, where “each boom will be deployed individually before deploying the entire reflector.” They expect this process to take “around five days” to finish.
Biomass Spacecraft Operations Manager Elia Maestroni said that this deliberate pace was a deliberate choice. “Precision and care are paramount in this meticulous and exceptionally long process,” she said. Because it requires this intense focus, they cut each shift short: Maestroni said that “we will adapt our schedule for the LEOP and rely on three shifts of eight hours instead of two of twelve.” She added that “the night shift will only be dedicated to monitoring the spacecraft.”
In an ESA release on Biomass, ESA’s Biomass Project Manager, Michael Fehringer, said that “after years of innovation and cooperation with the scientific community and the space industry, we’re more than excited to see the satellite ready for launch.” He added that they hope that the mission “will advance our ability to quantify forest carbon stocks and fluxes.”
