Comparison of three field methods for forest canopy closure modelling with Landsat imagery

Forest canopy closure is one of the most important structural characteristics linked to the spatial distribution of forest flora and fauna. Quick and cost effective methods are needed to map canopy closure over large areas. This study was designed to evaluate Landsat ETM+ imagery in the modeling of canopy closure in temperate hardwood forests. Three common instruments used to measure canopy closure in the field were compared against each other and then in regression-based modeling using Landsat spectral and spatial information. The three methods of measuring canopy closure were the Trac (Tracing Radiation and Architecture of Canopies), sighting tube and hemispherical photography. It was found that hemispherical photography was the most consistent and least biased method. Use of automated binary thresholding of the hemispherical images was essentially no different than manual thresholding but provided stronger closure models using the Landsat imagery. In modeling canopy closure, it was found that spectral green band data and textural measures of the green and thermal bands had weak but significant relationships with canopy closure. (Abstract shortened by UMI.)...