Estimation of LAI and FAPAR by constraining the leaf and soil spectral characteristics in a radiative transfer model
Abstract:We evaluated the estimation of the leaf area index (LAI) and the fraction of absorbed photosynthetically active radiation (FAPAR) of green plant canopies from top-of-the-canopy (TOC) spectral indices by using the PROSAIL model under the possible constraints of leaf and soil spectra. For the LAI estimation, the ratios (B1 - B3)/(B1 + B3) and B1/B3 provided fewer estimation errors than (B4 - B3)/(B4 + B3) or B4/B3 when the variation in the soil spectral reflectance was small or LAI was large. Here, B1, B3 and B4 denote the blue, red and near-infrared bands of Landsat ETM+, respectively. For the FAPAR estimation, the ratios (B5 - B7)/(B5 + B7) and B5/B7 provided fewer estimation errors than (NIR - R)/(NIR + R) or NIR/R for a FAPAR value of 0.3-0.7 when the variation in the soil spectral reflectance was large. Here, B5 and B7 denote the bands with wavelengths 1.55-1.75 and 2.09-2.35 m, respectively. These were maintained for various conditions of the solar incident zenith angle (s), leaf angle distribution (LAD), canopy hotspot parameter (s 1) and clumping index (Ω).
Document Type: Research Article
Affiliations: 1: Center for Far Eastern Studies, University of Toyama, Gofuku, Toyama, Japan 2: Graduate School of Systems and Information Engineering, University of Tsukuba, Tennodai 1-1-1, Tsukuba, Japan
Publication date: March 1, 2010