- Alejandra Martins
- BBC News World
Right now, a shower of laser pulses is coming to Earth from the International Space Station (ISS).
And their goal is to reveal even the most intimate secrets of the planet’s forests.
The GEDI mission, jointly developed by NASA’s Goddard Space Flight Center (US space agency) and the University of Maryland, USA, enables unprecedented 3D mapping of forested areas even in the most remote locations.
“It’s a satellite the size of a refrigerator, it weighs about 500 kilograms and is docked or connected to one of the modules of the International Space Station”, explained to BBC News Mundo, the BBC’s Spanish-language news service, Spanish scientist Adrián Pascual, member of the GEDI scientific team, specialist in mapping and management of forest ecosystems and professor at the University of Maryland.
Mission data is critical to understanding how much carbon forests store and the impact of deforestation on the fight against climate change.
But the future of GEDI is uncertain — and currently a campaign seeks to ensure the continuity of the mission.
How does GED work?
GEDI is the acronym for Global Ecosystem Dynamics Investigation.
And the heart of the program is an instrument that shoots laser beams and has been docked to the International Space Station since 2019.
“The ISS orbits the Earth non-stop. And our GEDI satellite emits laser pulses all the time”, explains Pascual.
These pulses of energy make it possible to determine not only the height of trees, but also the structure of forests.
“When this pulse of energy reaches Earth, it hits the first element it encounters, which are the treetops, and continues to advance until it hits the ground.”
“The sensor measures the difference between the moment when the tops of the trees and the ground are detected. And by converting this time interval into distance, we can estimate the height of the vegetation.”
To reveal the composition of the forest, GEDI researchers study changes in energy wave patterns.
“In this way, we are able to estimate different levels of vegetation, and this gives us an idea not only of the height of the forest, but also of its structural complexity.”
GEDI uses a distance detection technology called LIDAR, which basically consists of pointing a laser at a surface and measuring the time it takes to return to its source.
It is not, however, a new technology.
“But this technology had never been put on a satellite and taken to the International Space Station and used at an altitude of more than 400 km to specifically monitor forests,” explains Pascual.
Carbon: the fundamental data
Trees capture CO2 or carbon dioxide from the atmosphere, one of the main greenhouse gases responsible for climate change.
And they store much of that carbon, preventing it from being released into the atmosphere.
“When trees grow, their biomass increases. And approximately 50% of this biomass, of the wood of these trees, is carbon”, says Pascual.
“It is estimated that a medium-sized tree, the most generic one imaginable, retains about 25 kg of carbon dioxide per year.”
“We use the GEDI to know then what is the stock, the storage of carbon that currently exists in all the forests of the world.”
The role of GEDI in the fight against climate change
The data and maps generated from the GEDI are publicly available.
And they are vital for governments around the world to realistically know what their carbon storage capacity is.
“In the case of many ecosystems, you don’t know how tall the trees are or what the forest is like,” says Pascual.
“There are regions in the Amazon and in remote places where we don’t know how tall the trees are and how the biomass is distributed.”
GEDI makes it possible to detect and quantify changes in biomass resulting from forest fires or illegal deforestation.
The GEDI data also reinforces the importance of preserving the world’s mature forests, rather than just prioritizing new forest plantations.
Many countries include tree planting in their CO2 emission reduction plans.
“It is true that it is necessary to plant more trees as part of the solutions to combat climate change, through projects to restore degraded areas with the potential to have vegetation again”, says Pascual.
However, “for many small trees to replace the carbon that a very large tree has stored, it takes a lot of small trees, time, and that there are no phenomena in the meantime, such as a felling, a fire or a pest attack.”
“We cannot fall into the trap of thinking that we can replace large stocks of carbon as in the Amazon, where there is a large amount of stored carbon, through plantations and restoration projects.”
Furthermore, the carbon stored in forests is not just found above ground.
“Underneath, in the roots of trees, the amount of carbon could be almost double what we are able to predict with GEDI. That’s why it’s vital to protect the ‘lungs’ of the planet.”
The campaign to save the GEDI
Developing GEDI and understanding how its technology works from a space station took nearly 20 years of prior work. Numerous scientific studies have been conducted by researchers such as Ralph Dubayah, GEDI’s principal investigator and professor at the University of Maryland.
The mission is scheduled to be operational only until the end of 2023, when the GEDI would be replaced by another instrument on the International Space Station.
Both researchers and government officials are currently supporting a campaign to prolong the life of GEDI in space.
One of the scientists who is not part of the mission but uses its data is Flávia de Souza Mendes, a Brazilian scientist based in Germany who is part of the RSATE research group (Remote Sensing Applied to the Tropical Environment).
For Mendes, GEDI plays a crucial role in mitigating climate change.
“Climate change will affect more people and countries from underrepresented and low-income groups. Free GEDI data can make a difference in supporting policymaking and research in low-income countries.”
On the other hand, “the carbon market is very heated at the moment and many companies are emerging that calculate the carbon stored in the forest or in reforestation and forestry projects to sell carbon credits”.
Adrián Pascual tells BBC News Mundo that “there is strong pressure from the international community to be able to maintain the GEDI for longer”.
“Because every week it’s up there, we have thousands and thousands of observations that allow us to come up with better estimates of vegetation height and biomass.”
“It’s a huge opportunity that we have to be able to keep him for a few more months or years, because we really don’t know when we’re going to have another opportunity like this.”
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