UCL measures forest carbon for the European Space Agency

Professor Mathias Disney, UCL Geography, used new technology to gain accurate measurements of forest carbon, in a consultancy project for the European Space Agency (ESA).

Understanding the amount of carbon stored in forests has a direct link with our future strategies to tackle climate change. The Global Climate Observing System (GCOS) has recognised above-ground biomass (AGB) as a key climate variable. AGB is the total amount of living and dead plant matter that is above the ground, and measuring it is a reliable way of measuring carbon storage in trees. A new technology based on 3D laser scanning is able to take more accurate AGB measurements than previously. Space agencies are interested in gaining these more precise measurements before they launch space-based methods for taking these observations.

ESA put out a call for experts to collect data for them using the new technology through a project called ForestScan. Professor Mathias Disney from UCL Geography won the bid to complete this project. Professor Disney’s work is internationally recognised, and he has particular expertise on the carbon cycle, how radiation interacts with the Earth’s surface, and process modelling of the terrestrial environment. He has led multiple field campaigns across tropical and temperate forests, worked extensively with space agencies including ESA and NASA, and his work on new satellite estimates of forest biomass has been cited by the Intergovernmental Panel on Climate Change (IPCC) as best practice for national greenhouse gas inventories. 

With support from UCL Consultants and subcontractors from University of Leeds, Wageningen University, AMAP/ IRD Research organisation, CIRAD Research, University of Edinburgh and University of Cambridge, Professor Disney was able to successfully complete this consultancy project for ESA.

Testing a new technology

“We don’t accurately know how much carbon is stored in forests,” Professor Disney explained. “We’re especially interested in tropical forests, because this is where a lot of carbon is, and it’s where some of the biggest threats are in relation to climate change too. Space agencies are launching a number of new satellite instruments that are looking at forests and carbon. But they will need to understand how good the information they gain from these missions will be. To do that, they need accurate data of carbon in forests. That’s where the ForestScan project stemmed from.”

In particular, ESA wanted Professor Disney and his team to collect data using two technologies – Terrestrial Lidar Scanning (TLS) and UAV Lidar Scanning (UAV-LS), to measure AGB. Previously, AGB has been estimated over small areas of approximately one hectare, using manual measurements of individual tree size and mathematical models. TLS is a ground-based, high-precision measurement using laser that can take measurements from individual trees. UAV-LS takes drone-based measurements using a laser pulsing method at larger scales but lower precision. Using these methods together, it’s possible to collect highly accurate AGB measurements on a wide scale. 

Through this consultancy project, Professor Disney and his team used these technologies to collect data in forests across Africa, South America and Southeast Asia. He explained that it’s still vital to take field based manual plot measurements too, in order to achieve the highest possible accuracy, and to be able monitor different areas of forest over time. “This ‘boots on the ground’ work is really valuable,” Professor Disney said. “We used 100 by 100 meter plots that have been laid out by ecologists, who measure the diameter of individual trees with tape measures, and identify the species. We tagged the trees too, so it’ll be possible to come back five years later and take the same measurements again. This could show us how the tree has grown, if it’s fallen over, or whether it’s even still there or not.”

Taking carbon measurements into space

It’s been widely discussed in the scientific community that the combination of ground-based measurements, remote sensing data and satellite data will provide the basis of our future understanding of carbon stores in forests. ForestScan captured a data set that can be used by the wider community now. But it’s also contributing to ESA’s forthcoming space mission, BIOMASS. This satellite will take measurements of forest biomass across the tropics.

As a result of ForestScan, Professor Disney discovered that previous measurement methods have underestimated how much carbon is in tropical forests. “This approach is a much more accurate way of collecting data, from the plot scale of one hectare, right up to whole region,” Professor Disney said. “If you want to collect data top down from satellites, you need a way of tracing the uncertainty from individual trees up through to thousands of hectares of rainforest. By doing this work in different continental regions and in multiple different plots, we've been able to say how good this approach is.”

Once ESA’s BIOMASS mission starts collecting data, the accuracy of the data the satellite retrieves can be compared against the mapped areas of carbon from this project. “ForestScan was a proof of concept,” Professor Disney said. “It helped us see how a forest biomass reference system like this could be scaled up, what the logistical challenges are, and what investment is needed. This kind of work can’t be done by one or two groups of people – you need 50 groups who all have resources and funding. The team we worked with on this are also working on the BIOMASS mission, and they really recognised the value of the work we did to drive that forward.””

As a direct result of the ForestScan findings, the Smithsonian Tropical Research Institute (STRI) was awarded $12 million for a project to continue measuring forest carbon in this way. Professor Disney is part of this group, and will be travelling to Angola, Peru and other global sites to take more measurements.