GEDI: A Tool for Forest Carbon Maps

Mark Altaweel

Updated:

The Global Ecosystem Dynamics Investigation (GEDI) system was launched in December 2018 on a Falcon 9 SpaceX rocket. One of the main goals was to use LIDAR technology to measure forest health, specifically the presence of trees, which can provide more accurate measurements in such areas as how much carbon is stored in various forests. [1] Forests are both a repository to store carbon, helping to avoid higher levels of CO2, but also a potential threat if carbon is release into the atmosphere when trees are cut or burned.

GEDI’s forest mapping technology

The technology aboard GEDI is similar to the pulsed laser light from LIDAR used to measure landscape features, often attached to aircraft. The laser pulse can be used to detect the top and bottom of a canopy of trees, where a dense pulse is sent to comprehensively cover the entire canopy.

This accurate way to measure will enable far better estimates of how much carbon is stored or potentially released in forests, which would provide more accurate carbon data to measure in climate models used to forecast future climate change. The laser pulse can fire 242 times per second, illuminating a 25m spot, which forms its best resolution, with a dense laser cover. There are three lasers that produce eight parallel tracks for observations, with each track separated by about 600 m distance.[2]

Data flow for generation of GEDI-derived information products to aid managers and policy makers in assessments, monitoring and decision making related to wildland fire. credit: Birgit Peterson.
Data flow for generation of GEDI-derived information products to aid managers and policy makers in assessments, monitoring and decision making related to wildland fire. credit: Birgit Peterson. Source: Gedi.umd.edu

Four levels for the data product produced by GEDI

Geolocated waveforms (Level 1), footprint canopy height and profile metrics (Level 2), gridded height and canopy metrics (Level 3), and footprint and gridded above ground carbon estimates (Level 4a and 4b). This provides effectively the raw data measurements of the canopy as well as the key estimates that are most beneficial from the product. [3]

The Ecosystem Demography model (ED) provides estimates of carbon stocks and fluxes over large areas at fine resolution. Source: GEDI products page

The reason why GEDI is so important is scientists have been increasingly using airborne methods to measure 3D surfaces, including in forests, to better capture measurements such as carbon content in forests.

Benefits of GEDI forest mapping

Since this launch in 2018, there have been other benefits derived from GEDI in addition to better measuring carbon storage in forests, particularly in areas such as measuring biodiversity. Although tropical rainforests are some of the most important ecosystems targeted by GEDI, this system onboard the International Space Station (ISS) has been effectively used in measuring forests in the United States.

A view of the forest on Palmyra Atoll, a tropical reef island in the Pacific. Photo: Kevin Lafferty, USGS Western Ecological Research Center. Public domain.
A view of the forest on Palmyra Atoll, a tropical reef island in the Pacific. Photo: Kevin Lafferty, USGS Western Ecological Research Center. Public domain.

In a recent study led by Northern Arizona University, GEDI was used to reconstruct in 3D entire forest structures, enabling much more accurate estimates of biodiversity found within forests. The technology aboard GEDI is similar to the pulsed laser light from LIDAR used to measure landscape features, often attached to aircraft. The benefit of GEDI is it can now provide data obtained from aircraft but from a spaceborne system, which means it provides global coverage.

The laser pulse can be used to detect the top and bottom of a canopy of trees, where a dense pulse is sent to comprehensively cover the entire canopy. In the study, information from GEDI was combined with field-based data to determine structure and relationship between tree biodiversity measured with data from the National Ecological Observation Network. Information on branches, leaves and needles, that is from the bottom to the top of canopies, could be measured using GEDI’s laser pulses.

With species’ information obtained in the field, the researchers could then determine the relationship between tree structures and biodiversity for larger forest areas, helping to show how large and dense forests are critical to tree biodiversity, enabling a more diverse range of species to thrive if trees can grow to different heights. Such results could be expanded to cover other regions outside of the US and the hope is now we can begin to better understand forest health in relationship to density and biodiversity found in forests. [4]

Such results are not constrained to the US. In another similar study looking at the variety of tree heights present in the forests of Northern Italy and Germany, forest plots with more diversity and variety of tree heights as measured by GEDI demonstrated more biodiversity in forests. As forest biodiversity is important for forest health, measuring the diversity for tree canopy heights helps to show how healthy forests are in these areas of Europe. This means that GEDI data can be used as a useful proxy to measure forest health in various types of forests. [5]

A view of the lower forest canopy and floor in a redwood forest.
GEDI data can be used as a useful proxy to measure forest health in various types of forests. Photo: Caitlin Dempsey, Henry Cowell Redwoods State Park.

Other recent work demonstrates both forest ecology diversity and carbon storage results using GEDI’s pulse laser capabilities and measurements are key results produced, where such results were produced in Tanzania’s forest regions. [7]

GEDI continues to monitor forest health

Forests are both a repository to store carbon, helping to avoid higher levels of CO2, but also a potential threat if carbon is release into the atmosphere when trees are cut or burned. The GEDI project was initially projected to last two years but the GEDI system continues to operate from the ISS, providing more data that can be used to monitor forest health, particularly in areas such as carbon storage. The GEDI project is led by the University of Maryland. The North Arizona University study and the study in Europe highlight how GEDI can also be used in other areas such as biodiversity [6].

The arrival of the GEDI system has been greatly welcome for scientists studying tree biodiversity as well as global carbon levels, as tree heights, including diversity of heights found within forests, can now be better measured, which helps to understand forest health and carbon capture in our forests. Combining these data with other data, including field-measured results, even enables the identification of specific tree species in forests using GEDI. Mapping techniques using LIDAR- based results were limited in scale previously given LIDAR was primarily obtained from aircraft. As long as GEDI can continue, more accurate forest biodiversity estimates, for much larger areas, can be developed while the initial goals for estimating the potential for forests to contain stored carbon could also be accomplished. 

References

[1]    For more on the GEDI project and the satellite, see:  https://www.earthdata.nasa.gov/sensors/gedi.

[2]    For more background and scientific details on GEDI, see:  Popkin, Gabriel. 2018. “Space Laser to Map Trees in 3D.” Science 362 (6420): 1226–1226. https://doi.org/10.1126/science.362.6420.1226.

[3]    For more on data products and tools that can be used along with the relevant data, see: https://gedi.umd.edu/data/products/.

[4] Hakkenberg, C R, J W Atkins, J F Brodie, P Burns, S Cushman, P Jantz, Z Kaszta, C A Quinn, M D Rose, and S J Goetz. “Inferring Alpha, Beta, and Gamma Plant Diversity across Biomes with GEDI Spaceborne Lidar.” Environmental Research: Ecology 2, no. 3 (September 1, 2023): 035005. https://doi.org/10.1088/2752-664X/acffcd.  An article discussing this work can be found here:  https://phys.org/news/2023-11-biodiversity-space-borne-lidar.html.

[5] Torresani, Michele, Duccio Rocchini, Alessandro Alberti, Vítězslav Moudrý, Michael Heym, Elisa Thouverai, Patrick Kacic, and Enrico Tomelleri. “LiDAR GEDI Derived Tree Canopy Height Heterogeneity Reveals Patterns of Biodiversity in Forest Ecosystems.” Ecological Informatics 76 (September 2023): 102082. https://doi.org/10.1016/j.ecoinf.2023.102082.

[6] For more on the GEDI project and the satellite, see:  https://gedi.umd.edu/

[7] Liang, Mengyu, Mariano González-Roglich, Patrick Roehrdanz, Karyn Tabor, Alex Zvoleff, Veronika Leitold, Julie Silva, Temilola Fatoyinbo, Matthew Hansen, and Laura Duncanson. “Assessing Protected Area’s Carbon Stocks and Ecological Structure at Regional-Scale Using GEDI Lidar.” Global Environmental Change 78 (January 2023): 102621. https://doi.org/10.1016/j.gloenvcha.2022.102621.

This article was originally written on December 20, 2018 and has since been updated.

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About the author
Mark Altaweel
Mark Altaweel is a Reader in Near Eastern Archaeology at the Institute of Archaeology, University College London, having held previous appointments and joint appointments at the University of Chicago, University of Alaska, and Argonne National Laboratory. Mark has an undergraduate degree in Anthropology and Masters and PhD degrees from the University of Chicago’s Department of Near Eastern Languages and Civilizations.

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