Measuring the leaf area index and foliage profile of forest canopies using a ground-based lidar instrument (EchidnaRTM).
详细信息
文摘
Effective leaf area index LAI) retrievals from a ground-based, upward-scanning, under-canopy, full waveform, near-infrared 1064 nm) lidar, the Echidna Validation Instrument EVI), agree with those obtained from both hemispherical photography and the Li-Cor LAI-2000 Plant Canopy Analyzer. A newly proposed approach for clumping index retrieval based on the three dimensional structure of gaps also produced clumping index measurements that were consistent with those of gap-size distribution theory using hemispherical photography, documenting the ability of the EVI to characterize the clumping of forest foliage at the stand scale. These results are based on trials at 28 plots within six hardwood and conifer stands at Harvard Forest, Massachusetts, Bartlett Experimental Forest, New Hampshire, and Howland Experimental Forest, Maine, from July 2007, and on additional 30 plots within six conifer stands in Sierra National Forest, California, from July 2008. These stands vary in tree heights, stocking densities, and local surface topography. In addition to LAI, foliage profiles leaf area with height), can be estimated from the EVI. These are difficult to retrieve from hemispherical photos or LAI-2000 measurements, but are easily derived from EVI observations of gap probability with zenith angle. The foliage profiles retrieved were consistent with stand structure as observed in the field and match well with those obtained from Lidar Vegetation Imaging Sensor LVIS) airborne large-footprint lidar system. Tree heights as determined from the foliage profiles retrieved by the EVI are also close to heights determined using the LVIS. LAI and foliage profile leaf area with height) are key biophysical parameters for assessing plant productivity, and for understanding atmosphere-vegetation exchange processes such as photosynthesis, evaporation and transpiration, and carbon flux. The accuracies of many modeling studies using LAI as a key input depend heavily on the accuracies of ground-truth LAI estimates. The Echidna Validation Instrument is the first realization of the EchidnaRTM lidar concept, devised by Australias Commonwealth Scientific and Industrial Research Organization CSIRO), for measuring forest structure using full-waveform, ground-based, scanning lidar.