Algorithms for Retreiving LAI and FPAR of Boreal Conifer Forests Using Landsat TM Image

Abstract

Algorithms have been developed for calculating leaf area index (LAI) and the fraction of phoyosynthetically-active radiation (FPAR) absorbed by boreal forests using satellite-measured vegetation indices. This study is part of the Boreal Ecosystem-Atmosphere Study (BOREAS). In the summer of 1994, ground-based measurements of LAI and FPAR were made in more than 30 forest stands near Candle Lake and Prince Albert, Saskatchewan and near Thompson, Manitoba. The measurements were made using optical instruments including the Plant Canopy Analyzer (PCA, LI-COR LAI-2000) and the TRAC (Tracing Radiation and Architecture of Canopies). The TRAC was recently developed by us to quantify the effect of canopy architecture on optical measurements of leaf area index and to obtain average PAR transmitted through the forest canopies. The stands with the ground-truth data were located on georeferenced Landsat TM images using global positioning system (GPS) measurements. Algorithms for LAI and FPAR are based on the correlation of the ground-based measurements with vegetation indices calculated using Landsat TM data. It is found that late spring Landsat images are superior to summer images for determining overstory LAI and FPAR in boreal conifer stands because the effect of the understory is minimized at the time.