Effect of Ground Surface Reflectance on LiDAR Waveforms, Height Metrics and Biomass Estimation

Forest attributes such as aboveground woody biomass are commonly derived from LiDAR waveforms using empirical relationships with relative height metrics, i.e., percentiles of returned energy relative to the ground elevation. However, LiDAR waveforms and height metrics are strongly influenced by the reflectance properties of vegetation, soils, and litter at or near the ground surface, adding a level of uncertainty to biomass estimates. To estimate this range of uncertainty, we used FLIGHT, a ray tracing radiative transfer model that simulates single and multiple scattering, to simulate the effect of realistic ground cover types in a mixed, intermediate-aged forest near Howland, Maine, USA. Simulated cover types included sphagnum moss, lichen, leaf litter, bare soil, and snow, which were evaluated for forest canopy cover ranging from 27 to 98%. We discuss multiple scattering in feature waveforms (i.e., reflected energy above the ground peak) and attempts to reduce biomass uncertainty by excluding potentially confounding ground returns.