ABSTRACT
A plant’s physiological state is governed by its biochemical constituents, including photosynthetic and other enzyme systems, structural and nonstructural carbohydrates, chlorophyll and associated light harvesting complexes, and photoprotective and ancillary pigments. Many biochemical processes, such as photosynthesis, net primary production, and decomposition, are related to the content of biochemicals in leaves [1-3]. Of these biochemicals, leaf chlorophyll content stands out as being both sensitive to environmental conditions and having a very strong inŸuence on leaf optical properties and canopy albedo [4-6]. All green leaves have major absorption features in the 400-700 nm range caused by electron transitions in chlorophyll and carotenoid pigments [7]. Most green vegetation shows absorption peaks near 420, 490, and 670 nm due to the strong absorption peaks of chlorophyll a and b. The absorption of other pigments in the leaf, such as carotenes and xanthophylls, is usually obscured by the absorption of chlorophyll a and b. Differences in leaf and canopy reŸectance between healthy and stressed vegetation due to changes in chlorophyll levels have been detected in the green peaks and along the red edge (701-740 nm) [8-12]. The changes of red-edge position and slope are associated with vegetation stress [9,13-15]. Canopy reŸectance in the green and far-red regions is also sensitive to variations in chlorophyll concentration and can act as an indicator of vegetation stress [10]. Leaf chlorophyll content is of great use for forest health
7.1 Introduction .......................................................................................................................... 167 7.2 Methods for Estimating Leaf Chlorophyll Content .............................................................. 168
7.2.1 Empirical Method for Leaf Chlorophyll Content Estimation................................... 168 7.2.2 Physically Based Model Inversion Method .............................................................. 169
7.2.2.1 Modeling Method for Broadleaf Chlorophyll Content Estimation ............ 170 7.2.2.2 Modeling Method for Needleleaf Chlorophyll Content Estimation .......... 172
7.3 Methods for Estimating Forest Canopy Chlorophyll Content .............................................. 175 7.3.1 Empirical and Semiempirical Methods .................................................................... 175 7.3.2 Physically Based Modeling Method ......................................................................... 176
7.3.2.1 Modeling Method for Closed Forest Canopies .......................................... 176 7.3.2.2 Modeling Methods for Open Forest Canopies ........................................... 177
7.4 Conclusions and Applications ............................................................................................... 180 Acknowledgments .......................................................................................................................... 182 References ...................................................................................................................................... 182
status evaluation and sustainable forest management [16,17]. Leaf chlorophyll content also serves as an input to photosynthesis and carbon cycle models. Changes in leaf optical properties and chlorophyll content, including responses to rising atmospheric CO2 and other global change variables, may have important implications to climate forcing as well [18].
