A Portable Lidar System for Rapid Determination of Forest Canopy Structure
Geoffrey
Parker, Smithsonian Environmental Research Center, parkerg@si.edu
David
Harding, NASA Goddard Space Flight Center, David.J.Harding@nasa.gov
Michelle
Berger, Smithsonian Environmental Research Center, bergerm@si.edu
Significant 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 to determine structure at scales consistent with the footprints of function measurements. We describe a portable system, assembled from commercially-available components, for acquiring measurements of distances to overhead plant surfaces that can be aggregated to assess canopy structure at scales of ecological interest. Deployed by a person from the forest floor, the system includes a narrow-beam, rapidly-pulsed, first-return laser rangefinder coupled with a data recording system.
From tests in an age-sequence of broad-leaved, closed-canopy forests we found the system provides 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 approaches, such as the “Foliage Height Profile” method. 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. Various field sampling schemes and methods of aggregating the measurements yield a variety of representations of structure, including mean profiles, tomographic sections, three-dimensional distributions of canopy surface density, and maximum height surfaces. Derivable summary measures include canopy cover and area index, porosity, the size distribution of overhead openings, and indices of structural complexity. Moreover, the approach can provide estimates of spatial variability and covariance not previously obtainable. Portable LIDAR systems such as the one we describe provide a new tool for measurement of small-scale forest structure useful in various canopy research and forest management applications.
Submetido por David Roy Fitzjarrald em 24-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)