Synergy of Airborne Laser Altimetry and Digital Videography for Individual Tree Crown Delineation

摘要

For forest inventory, laser altimetry can provide an alternative to conventional stereoscopic methods or field measurements to obtain forest stand heights, an important factor in the inference of numerous other forestry parameters. When the density ofLIDAR data becomes high enough, one can think in terms of individual tree heights. New systems could incorporate individual tree crown (ITC) delineation and species recognition from multispectral imagery with ITC-based height measurements from LIDAR data to produce precise, accurate and timely ITC-based forest inventories. Volume and biomass inferences could then be done on an ITC-basis. This study examines three aspects of the synergy between airborne laser altimeter data and multispectral video imagery: (a) the elimination of non-forested or poorly forested areas from the analysis of mature forests, (b) the potential improvements in ITC delineation, and (c), the possibility of a separate ITC analysis of young regenerating areas. A combination of masks generated from multispectral rules and by selecting a minimum LIDAR height led to a very good separation of the forested areas, and even of individual trees in open fields. The ITC delineation process was then applied to the unmasked forested areas, first on a smoothed version of the near infrared image and then, on a smoothed version of the LIDAR height image. Both cases produced numerous tree clusters rather than individual tree crowns, but for different reasons. A post-processing combination of both results led to superior crown delineation, with few tree clusters.