Primary and secondary controls on measurements of forest height using large-footprint lidar at the Hubbard Brook LTER.
KNOX, R.G.* 1, J.B.BAIR 1, P.A.SCHWARZ 2, M.A.HOFTON 3 and R.DUBAYAH 3
NASA's Goddard Space Flight Center, Greenbelt, MD 20771 USA 1
Cornell University, Ithaca, NY 14853 USA 2
University of Maryland, College Park, MD 20742 USA 3
On September 26, 1999, we mapped canopy structure over 90% of the Hubbard Brook Experimental Forest in White Mountain National Forest, New Hampshire, using the Laser Vegetation Imaging Sensor (LVIS). This airborne instrument was configured to emulate data expected from the Vegetation Canopy Lidar (VCL) space mission. We compared aboveground heights of the tallest surfaces detected by lidar with average forest canopy heights estimated from tree-based measurements in or near 346 0.05 ha plots (made in autumn of 1997 and 1998). Vegetation heights had by far the predominant influence on lidar top heights, but with this large data set we were able to measure two significant secondary effects; those of steepness or slope of the underlying terrain and of tree crown form. The size of the slope effect was intermediate between that expected from models of homogeneous canopy layers and for solitary tree crowns. The first detected surfaces were also proportionately taller for plots with more basal area in broadleaved northern hardwoods than for mostly coniferous plots. We expected this because of the contrast between the shapes of cumulative distributions of surface area for elliptical or hemi-elliptical tree crowns and those for conical crowns. Correcting for these secondary effects, when appropriate data are available for calibration, may improve vegetation structure estimates in regional studies using VCL or similar lidar data sources.
Keywords: laser altimetry, tree, canopy, slope, crown form
This abstract is being presented at: 2:15 PM in session:
Oral Session #64: Remote Sensing.