PARENT SESSION
Oral Session #71: Remote Sensing and GIS.
Presiding: J.D. Allan
Wednesday, August 7. 1:00 PM to 4:45 PM. Palo Verde Room, Radisson.
A portable lidar system for rapid determination of forest canopy structure.
Parker, Geoffrey*,1, Berger, Michelle1, Harding, David2, 1 Smithsonian Environmental Research Center, Edgewater, MD2 NASA Goddard Space Flight Center, Greenbelt, MD
ABSTRACT- Important functional characteristics of forests are related to the organization of their canopies. However, understanding of the relation between canopy structure and function has been limited by a lack of methods for determination of structure at scales consistent with the footprints of function measurements. We describe a portable system, assembled from commercially-available components, for acquiring measurements that can be used to rapidly assess canopy structure at scales of ecological interest. Deployed by a person from the forest floor, the system includes a closely collimated, high-frequency, first-return laser rangefinder coupled with a data recording system. Various field sampling schemes and methods of aggregating the measurements of distances to overhead surfaces yield a variety of representations of structure, ranging from mean profiles to tomographic sections to three-dimensional distributions of canopy surface density. From tests in an age-sequence of broad-leaved forests we found the system provides repeatable results significantly more rapidly than previous methods, at spatial scales as small as 1 m in all dimensions. The estimated mean vertical canopy structure is consistent with that found from more laborious, manual methods (such as the "foliage height profile"). Moreover, the approach can provide estimates of spatial variability and covariance not previously obtainable. The structure revealed by the system is sensitive to canopy changes in time (from repeated measurements in particular locations) and transitions in space (at boundaries between forests and at edges). The system has some biases due to beam width and range averaging but from a variety of tests we found these have relatively little effect on the structure estimates. We expect systems such as the one we describe will be useful for various canopy research and forest management needs.
KEY WORDS: canopy, structure, three-dimensional, organization