針葉樹における分光反射率と葉面積指数の関係：森林の三次元構造とクランピングの影響

摘要

Toward the reliable estimation of leaf area index (LAI) and fraction of absorbed photosynthetically active radiation (FAPAR), the relationship between LAI/FAPAR and bidirectional reflectance factor (BRF) at the top of canopy should be accurately modeled by the radiation transfer models. These relationships vary with the forest landscape due to its horizontal heterogeneity and needles clumping within shoot. In this study, the eifect of the forest heterogeneity on the relationships between BRF and LAI, and NDVI and LAI/FAPAR were examined through the three-dimensional radiative transfer simulation, and were compared with the results from one-dimensional radiative transfer simulation. In addition to the simulation, limitation of one-dimensional radiative transfer simulation was evaluated. The results showed that BRF at red and near infrared, and NDVI had large variations with different forest landscape under the same LAI conditions. However the relationship between NDVI and LAI, and NDVI and FAPAR derived from dense canopy condition were quite similar to the results from one-dimensional model. If we add the shoot clumping effect in one dimensional radiative transfer model as a universal parameter for three-dimensional effect of the forest, one dimensional radiative transfer model can work well for the BRF simulation in spatially heterogeneous landscape except higher LAI conditions.%近年，衛星データによる葉面積指数（Leaf Area Index， LAI）や光合成有効放射吸収率（Fraction of Absorbed Photosynthetically Active Radiation，FAPAR）などの各種衛星 データセットが容易に利用できるようになってきた。ま た，植生の放射伝達モデルの普及や様々な植生指数を用い た関係式の提案により，研究対象とする地域のLAIや FAPARの推定が容易になってきた。