Algorithm Theoretical Basis Document (ATBD) for GEDI L2B Footprint Canopy Cover and Vertical Profile Metrics

Accurate measurements of vertical forest structure at a global scale are critically important to advance our knowledge of terrestrial ecology and biodiversity. NASA’s Global Ecosystem Dynamics Investigation (GEDI) mission aims to fill current observation gaps by collecting the first high-resolution lidar observations of the 3D structure of the Earth and providing spatially dense samplings of forest structure between ~52° N and ~52° S. The GEDI instrument consists of 3 lasers producing a total of 8 beam ground transects that are spaced approximately 600 m apart on the Earth’s surface in the cross-track direction. Each beam transect consists of ~25 m footprint samples approximately spaced every 60 m along track. The fundamental footprint observations made by the GEDI instrument are received waveforms of energy as a function of receive time. These are combined with laser pointing and positioning information for precise geolocation and post-processed to determine ranging points of reflecting surfaces with the waveform footprint. The waveforms provided in the L1B product and locations of reflecting surfaces within the footprint provided in the L2A product are then used to derive the directional gap probability profile and extract biophysical metrics from each GEDI waveform. These metrics include canopy cover, Plant Area Index (PAI), Plant Area Volume Density (PAVD) and Foliage Height Diversity (FHD). This ATBD presents the algorithm and approach used to determine these biophysical metrics within the GEDI waveforms.