Science Overview
GEDI provides high quality laser ranging observations of the Earth’s forests and topography required to advance our understanding of important carbon and water cycling processes, biodiversity, and habitat.

The science of GEDI is centered on answering three key questions, given below. GEDI answers these questions through science objectives that require collecting data on forest structure needed to quantify the current and future state of forest resources related to carbon and biodiversity.

 GEDI science questions and objectives.

GEDI has three science questions:

  1. What is the carbon balance of the Earth’s forests?
  2. How will the land surface mitigate atmospheric CO2 concentrations in the future?
  3. How does forest structure affect habitat quality and biodiversity?

GEDI has four science objectives designed to address these questions:

  1. Quantify the distribution of aboveground carbon stored in vegetation
  2. Quantify the effects of vegetation disturbance and recovery on carbon storage
  3. Quantify the potential for existing and new/regrowing forests to sequester carbon in the future
  4. Quantify the spatial and temporal distribution of habitat structure and its influence on habitat quality and biodiversity

Carbon Balance and the Earth’s Forests

Forests absorb (or “sequester”) CO2 from the atmosphere and act as carbon “sinks”. This absorbed carbon is used to drive plant growth and is stored as biomass. About 50% of tree’s weight or biomass is in the form of carbon. When forests are disturbed through natural or human causes, such as fire or deforestation, they release this stored carbon back into the atmosphere. The release of this forest carbon (a carbon “source”) is the second largest source of atmospheric CO2 (behind fossil fuel emissions). But forests are estimated to absorb about ⅓ of the fossil carbon emitted per year.

Annual deforestation from 2000 to 2016 mapped using Landsat imagery. The yellow to red color gradient indicates deforestation occurring closer to 2000 or 2016, respectively.


There is great uncertainty about the magnitudes of carbon emitted and absorbed by forests. This uncertainty is captured in the idea of a “missing sink” of carbon. When we do a global accounting of the sources and sinks of carbon, which should be equal because the carbon must go somewhere, there is an imbalance: there is some emitted carbon that cannot be accounted for. One hypothesis is that forests act as this missing sink.

GEDI data are used to reduce uncertainty in our knowledge of the net impacts of carbon loss through deforestation and carbon gain through forest regrowth by quantifying the current biomass of the Earth's forests. When these data are combined with disturbance data, they provide a window into understanding the net impact of forest disturbance and subsequent regrowth. This in turn resolves questions about the global carbon balance of the Earth-atmosphere system and the missing sink of carbon.

How Much Carbon will Forests Absorb in the Future?

Young, rapidly regrowing forests absorb carbon at higher rates than mature forests. What impact will cutting down forests or planting new forests have on concentrations of atmospheric CO2 through time?

Illustration showing major elements of the global carbon cycle.


Quantifying the carbon sequestration trajectory of existing forests as well as reforestation and afforestation on other lands is key to creating better management and policy aimed at reducing CO2 emission. The best way to ask “what if” questions is through prognostic ecosystem models that allow us to model the impacts of land use change that may result from increased urbanization, changing agricultural activities, or implementation of policy goals such as maintaining or increasing forest areas. The key to utilizing such models is accurate information on the current biomass status of forests. This provides an accurate starting point from which potential carbon sequestration trajectories can be estimated. GEDI provides these data, and when married to ecosystem models, provides the capacity for evaluating alternative conservation and development strategies.

Habitat Quality and Biodiversity

Species declines can be primarily attributed to loss and fragmentation of habitat, particularly in tropical biomes where species abundance has decreased over the past three decades by about 50%. Rapid rates of species extinctions (~50,000 per year) are projected to rise in this century unless measures are taken to reduce deforestation, expand and connect protected area networks, and mitigate the negative effects of climate change.

Forest canopy structure, such as measured by GEDI, is key towards helping us understand the status of forest biological diversity at regional and global scales. For example, the diversity and abundance of many bird species are known to depend critically on forest canopy profiles, that is, how leaves and branches are arranged vertically.

GEDI represents a critical step towards global habitat mapping through its detailed characterization of local and regional ecosystem structure, enabling new investigations into the role of structure, and furthermore providing a basis from which predictive biodiversity models can be used to understand the impact of changing land use and climate on habitat quality, species richness, and abundance.

What is ecosystem structure?

Ecosystems can be characterized by their structure, function and composition. Together, these aspects influence processes such as biogeochemical fluxes and properties such as carbon stocks, habitat quality, and biodiversity. Ecosystem structure refers to the horizontal and vertical distribution of ecosystem elements and their interactions. For example, landscape structure can be characterized by the horizontal distribution of canopy gaps within a forest. On a more local scale, vegetation structure can be characterized by the vertical distribution of stems, branches and leaves. GEDI provides high spatial and vertical resolution measurements of ecosystem structure.

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