Effects of forest spatial structure on large footprint lidar waveform

Large footprint lidar has demonstrated its great potential for accurate estimation of many forest parameters, e.g., forest height, forest biomass and vertical structure of forest canopy. In addition to the canopy vegetation, many factors such as atmosphere, underlying surface, the shape of crown, et al., influence the lidar waveform. The illuminating intensity of the laser beam across the lidar footprint is a Guassian distribution and reduces from 1.0 to e-2 from the center to the edge of the footprint. Hence the forest stand structure plays an important role in the lidar waveform. The contribution of each tree to the lidar waveform varies with its location in a forest stand. This paper simulated the random, uniform and clumped tree distribution patterns in a stand. Then waveforms were simulated using a three dimensional lidar waveform model developed by Sun and Ranson. The results show that the tree distribution patterns affect the lidar waveform profiles. The area (or energy) under the waveform from vegetation (AWAV) and the height of median energy (HOME) were used to estimate the effects. Following trends have been revealed from the simulation: for AWAV and HOME, uniform > random > cluster. There is no obvious difference between regular and random. The waveform area (AWAV) varies much more than HOME. For the clumped case, the number of clusters does not have much effect on the lidar waveform