Forests exhibit dynamic responses to changes in environmental conditions and the impact of anthropogenic activities. Direct and accurate measurements of vegetation structure and its dynamics across large geographical areas are not yet available, preventing a comprehensive evaluation of their role in ecosystem services and application to environmental protection and biodiversity conservation. Spaceborne light detection and ranging (lidar) technology can potentially fill this observational gap and advance our understanding of tropical forest ecology, improving on the successes of NASA's Ice, Cloud, and land Elevation Satellite (ICESat) mission deployed between 2003 and 2009. To continue the global observation of vegetation structure, two new spaceborne lidar missions - ICESat-2 and the Global Ecosystem Dynamics Investigation (GEDI) - were successfully launched in late 2018. These lidar missions form the basis for synergistic and global observations of vertical canopy structure that will enable exploration of ecosystem dynamics at time scales ranging from seasonal to decadal.
Results/Conclusions
Here we present the algorithm theoretical basis and demonstrative products of ICESat-1 and GEDI. These include Canopy Cover Fraction (CCF), Leaf Area Index (LAI), and their vertical profiles. Performance assessment results using airborne lidar data products and in situ measurements (e.g. terrestrial laser scanner) show that these products can accurately detect canopy structure dynamics over dense forests of canopy cover exceeding 80%, where saturation often occurs for conventional passive optical remote sensing. Applications of these products have also led to several new discoveries in forest ecology and biodiversity studies. In sum, we anticipate spaceborne lidar missions can complement current satellite observations by providing unprecedented 3D information on biophysical stratification and change estimates in canopy structure for global forests.