The Global Ecosystem Dynamics Investigation (GEDI) system recently launched in December 2018 on a Falcon 9 SpaceX rocket.
This new satellite promises the first capability in 3D mapping of temperate and tropical forests. The maps created by this satellite system will enable a detailed measurement of the carbon content of forests, allowing scientists to determine how forests are releasing or taking up carbon.
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. Overall, the mission is expected to last two years, although there could be a future extension based on the success of this first project.[1]
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 on GEMNI, 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]
There are four levels for the data product produced by GEDI.
This will be 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.
The University of Maryland has taken the lead in this project and is hosting data and data products that derive from the satellite. Data are becoming available and in the months to come far more information will be available that scientists can begin to immediately apply.[3]
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.
The main limitation is that such technologies were not global in scale, in that LIDAR used was mounted on aircraft or on devices that did not fully allow easy global estimates. Using a global and high resolution satellite, where data will allow also far less interpolation for more accurate modeling of carbon release or capture/storage, will enable much better overall carbon estimates not only in forests but on the planet as well.[4]
Demonstrating the relatively high inaccuracies currently present, in Europe, an area where data are relatively more available for forests, a recent paper has demonstrated that our biomass estimates for forests are generally inaccurate to the point that limit a good understanding of carbon content. In fact, error ranges can be about 29–40% at national levels and up to 63–72% for cell-level data.[5]
The arrival of the GEDI system will be a welcome to scientists studying global carbon levels, as they now, for the first time, have a way to measure an important variable in places where it is often densely concentrated. Mapping techniques before were limited in scale or were difficult to utilise at global levels at any high accuracy. With the availability of GEDI, better climate change estimates are a likely output as well as better forecast models that monitor the change of our temperate and tropical rainforests.
References
[1] For more on the GEDI project and the satellite, see: https://www.nasa.gov/feature/goddard/2018/gedi-to-measure-earths-forests.
[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] For more on methods that can be used for mapping of forests, see: Bourgoin, Clément, Lilian Blanc, Jean-Stéphane Bailly, Guillaume Cornu, Erika Berenguer, Johan Oszwald, Isabelle Tritsch, et al. 2018. “The Potential of Multisource Remote Sensing for Mapping the Biomass of a Degraded Amazonian Forest.” Forests9 (6): 303. https://doi.org/10.3390/f9060303.
[5] For more on errors produced in using available map data in Europe for measured volume in forested areas, see: Avitabile, Valerio, and Andrea Camia. 2018. “An Assessment of Forest Biomass Maps in Europe Using Harmonized National Statistics and Inventory Plots.” Forest Ecology and Management409 (February): 489–98. https://doi.org/10.1016/j.foreco.2017.11.047.
