Characterising the Vertical Canopy Structure of Vegetation and its Impact on Radiation Regimes using Spaceborne LiDAR

Forests are the most complex ecosystem on the planet and and play a crucial role in the exchange of mass and energy between the land surface and atmosphere. India's tropical region encompasses a diverse range of ecosystems, including deserts, mangroves, shrublands, deciduous, and evergreen forests, contributing to its ecological diversity. The varied canopy structural attributes of these vegetation types impact the exchange of carbon and water fluxes between the land surface and the atmosphere. We use high-resolution spaceborne data from the Global Ecosystem Dynamics Investigation (GEDI) to map the variability of vegetation canopy attributes at a synoptic scale. The total canopy height (RH100), foliage density (PAI) and foliage height diversity (FHD) demonstrated wide variability across the country and clearly differentiated the forested regions from the other land covers. The distribution of the canopy structural attributes in the forested regions and biomes also exhibited significant change across the years 2019-2021 with p-value < 0.05 (from the Kolmogorov–Smirnov test). Further, we fitted α and β (shape and scale) parameters of the Beta distribution function to the PAVD data from GEDI to compactly represent the spatial variation of the vertical variability of canopy. The high coefficient of determination (R² = 0.80) between the fitted beta distribution function and GEDI-PAVD suggests an effective representation of canopy vertical variability. Based upon the fitted parameters α and β, k-means clustering was performed which resulted in six distinct canopy structure classes. Differing canopy structures led to significant variations in radiation regimes throughout the day. Our observations suggest that incorporating Beta distribution-fitted shape and scale parameters into multi-layer canopy models enhances the estimation of flux exchanges over terrestrial ecosystems by capturing vertical variations in canopy structure.

Keywords: GEDI, Canopy structure, Plant area volume density, Beta distribution function