Friday, August 10, 2007
Exhibit Halls 1 and 2, San Jose McEnery Convention Center
LiDAR (light detections and ranging) has been successfully applied to the measurement of forest biophysical properties in a variety of environments. As part of a broader study correlating changes in barrier island forest structure with changes in freshwater availability, we tested the accuracy of forest measurements made with the EAARL (Experimental Advanced Airborne Research LiDAR). Deployed by NASA at Wallops Island, VA, EAARL is an airborne, full-waveform-returning, small-footprint LiDAR (nominal 20cm horizontal footprint). A full EAARL waveform is the amplitude of backscatter energy from reflecting surfaces per vertical “bin” (vertical resolution is generally 50cm) during the total travel time of a pulse through 3-dimensional space. Mission planning, and LiDAR and flight data processing are performed by a team comprised of NASA and USGS personnel. The loblolly pine (Pinus taeda L.)-dominated forests of Parramore Island (Virginia Coast Reserve Long Term Ecological Research Site) and the Maryland portion of Assateague Island (Assateague Island National Seashore, National Park Service) were surveyed with the EAARL in August 2004. Ground truth data were collected in study plots chosen to cover a range of elevations and the resultant depths to the freshwater table. Several EAARL LiDAR metrics that approximate familiar biophysical properties like plant surface area, canopy height, canopy cover, above-ground biomass, and vertical stratification were calculated from waveform data. We tested these for correlations with ground-based measurements and compared the predictive power of various resolution "composite" waveforms (raw waveform data merged to create larger synthetic footprints). We will further develop these techniques to a repeatable methodology to assess impacts of incremental sea-level rise on forest structure through changes to freshwater dynamics and availability. Utilizing a combination of EAARL metrics will likely provide for accurate estimations of changes in structure on scales applicable to water availability.