The amount of carbon stored in Earth's forests and how it is changing will be measured in the forthcoming Climate Change Initiative Biomass project, in which the legacy of GlobBiomass will be carried forward to the Sentinels' era.
Started in 2015, ESA's GlobBiomass project came at a time when there was a pressing demand for a complete characterisation of Earth's biomass. This need arises because about half of biomass is carbon, so the large-scale biomass changes occurring in forests modify Earth's global carbon balance, with profound effects on climate.
Measuring the biomass of every single tree on Earth would solve this problem, but this is unrealistic. The key scientific question addressed by GlobBiomass, therefore, was to use satellite data to estimate just how much carbon is stored in forests on our planet and to clarify its dynamics. It began when only a handful of continental-scale biomass datasets were available and all were being highly debated.
Over the last 30 years, scientists have recognised that biomass can be estimated in a variety of ways from remote sensing, but indirectly, since satellite sensors do not "see" forest biomass. This has generated a large literature on biomass estimation, but it is generally agreed that no one single satellite or algorithm would give the best estimate of biomass worldwide.
In GlobBiomass, the aim was to generate the "best possible" map of forest biomass for 2010. However, experts knew from the beginning that the map would only be an interim product, because the available satellite data had limited sensitivity to biomass.
At that time, the European Union's Copernicus Sentinels were being built, and scientists wanted to make sure that the multiple and repeated views by the fleet of Sentinel satellites would fit into the biomass estimation concept developed in GlobBiomass. They therefore developed a scheme that would be able to ingest future Sentinel data.
Senior project scientist at GAMMA Remote Sensing and one of the leaders of GlobBiomass, Maurizio Santoro, says, "After three years of intense work and cooperation with all teams involved in the project, we achieved our goal and went even beyond what we first expected. We obtained a global portrait of forest biomass at high resolution that is spatially consistent and is validated with biomass measured on the ground.
"Of great importance for communities intending to use the map is that we attached a measure of the uncertainty to each pixel and ensured that the methods used to estimate biomass are fully documented."
Climate Change Initiative (CCI) Biomass project picks up where GlobBiomass left off, but with a much sharper focus on the role of biomass in climate. It is therefore not just about developing better algorithms and better data to estimate biomass, but ensuring that the products fit the needs of the climate modelling community.
As a result, it requires much closer working with the global carbon cycle and climate community, and the CCI-Biomass team has been chosen to achieve this.
Although the GlobBiomass algorithms form the backbone of CCI-Biomass, there will be a major effort to identify the weaknesses in this approach in different biomes, and develop methods to correct these.
Climate-quality data must come with known accuracy in order to be assimilated into carbon cycle and climate models. Hence, a key part of the project is establishing an accurate in situ data set, especially in the tropics, to underpin a well-defined validation plan. The acid test of the products, however, will be how successful climate scientists are in testing and improving a range of climate models by using these data.
Shaun Quegan, the Biomass mission Principal Investigator and CCI Biomass Science Lead, commented, "GlobBiomass looked to the future, and CCI-Biomass must do the same. The Sentinels are already here, but we are entering an era when three new missions, NASA's Global Ecosystem Dynamics Investigation Lidar (GEDI) launching in 2018, and ESA's Biomass and the NASA-ISRO NISAR, both of which will launch around 2022, will provide unprecedented opportunities to measure forest biomass, structure and dynamics.
"CCI-Biomass will not simply be a project but a process, heading towards ever better measurement of forest structure, biomass and dynamics as our Earth observation capabilities improve."
About the Sentinels
The Sentinels are a fleet of dedicated EU-owned satellites, designed to deliver the wealth of data and imagery that are central to Europe's Copernicus environmental programme.
In partnership with EU Member States, the European Commission leads and coordinates this programme, to improve the management of the environment, safeguarding lives every day. ESA is in charge of the space component, responsible for developing the family of Copernicus Sentinel satellites and ensuring the flow of data for the Copernicus services, while the operations of the Sentinels have been entrusted to ESA and EUMETSAT.