GEDI canopy cover assessment using airborne LiDAR across eco-climate regions of the United States.

Information about woody plant density and canopy cover is central to our definition of terrestrial ecosystem types and crucial for understanding ecosystem state, dynamics, biogeochemical processes, and biodiversity. The Global Ecosystem Dynamics Investigation (GEDI) LiDAR on the International Space Station (ISS) samples 3-D structural information on woody vegetation structure, including an estimate of canopy cover in each 25 m diameter footprint. This study presents an evaluation of the GEDI fractional canopy cover estimates by comparing GEDI retrievals to high-resolution airborne laser scanning (ALS) data at 20 study sites with ~460,000 GEDI footprints across the United States. Based on the statistical assessment, we observed high correlations (R2 = 0.84 without geolocation correction; R2 = 0.96 with geolocation correction) with a Root Mean Square Error (RMSE) of 14.1% (without geolocation correction) and 7.2% (with geolocation correction). However, error in GEDI L2B canopy cover in some eco-climate regions is still significant, particularly in drylands (mean relative error (MRE) = 69.8%) and shrublands (MRE = 84.1%). The analysis also determined that the GEDI fractional cover retrievals are most effective when actual canopy cover is low (<20%) or high (>70%), with errors typically inflated in areas where canopy cover is in the 20-70% range. This study provides a baseline evaluation of GEDI canopy cover accuracy across eco-climate regions of CONUS, supporting improved interpretation and future refinement of the GEDI canopy cover product.