Forest Canopy Heights in Amazon River Basin Forests as Estimated with the Geoscience Laser Altimeter System (GLAS)

Land-use change， mainly forest burning， harvest， or clearing for agriculture， may compose 15 to 40 percent of annual human-caused emissions of carbon (C) to the atmosphere. Spatially extensive data on forest C pools can validate and parameterize atmospheric and ecosystem models of those fluxes and quantify fluxes from forest change. Excellent evidence exists that light detection and ranging (lidar) waveforms can be scaled to estimate forest biomass and aboveground C pools. The Geoscience Laser Altimeter Systmem (GLAS) instrument provides satellite-based continuous return lidar data and may provide a way to inventory forest C pools globally. It was launched aboard the Ice， Cloud and Land Elevation Satellite (ICESat) on January 12， 2003. Here we explore whether GLAS data may support global inventory of forest C pools using the Amazon river basin as a study area. Forest C budgets in Amazonia are globally significant. However， globally-derived and validated Amazonian forest biomass-waveform relationships are not yet available. Consequently， here we address only vegetation canopy height. Over the Amazon basin， lands with at least 75 percent tree cover had GLAS-measured canopy heights averaging 30.48±0.35 m (N = 2127). Fifty percent of measurements ranged from 25-35 m， agreeing with ground-based measurements in tierra firme forest. Lands with at least 60 percent tree cover had average canopy heights of 29.69±0.10 m (N=2734). Regression-based mapping models relating waveform widths to data from maps of tree cover and elevation， or those variables plus generalized soil type， explain 36 to 47 percent of observed variation in mean vegetation canopy heights where tree cover is at least 20 percent. Finally， secondary forest age， as mapped with time series data over an area spanning three adjacent Landsat scenes in Rondonia， Brazil， was significantly related to GLAS-derived height. These results provide evidence that GLAS waveforms can contribute to global inventories of forest C pools. (In: Aguirre-Bravo， C.; Pellicane， Patrick J.; Burns， Denver P.; and Draggan， Sidney， Eds. 2006. Monitoring Science and Technology Symposium: Unifying Knowledge for Sustainability in the Western Hemisphere Proceedings RMRS-P-42CD. Fort Collins， CO: U.S. Department of Agriculture， Forest Service， Rocky Mountain Research Station. p. 802-808)