IMPROVEMENT OF LAI-VI RELATIONSHIP FOR GROSS PRIMARY PRODUCTIVITY ESTIMATION IN DECIDUOUS BROADLEAF FOREST, JAPAN

摘要

The Moderate Resolution Imaging Spectroradiometer (MODIS) is the primary NASA Earth Observing System instrument monitoring the seasonality of global terrestrial vegetation. MODIS products, such as the MODIS Vegetation Index (VI), Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), and Leaf Area Index (LAI), are commonly used in ecological modeling. In this study, the 3-PGS (Physiological Principles Predicting Growth using Satellite data) model was used to generate gross primary productivity (GPP) using absorbed photosynthetically active radiation (APAR) based on the relationship of LAI and NDVI to environmental factors. We also examined the LAI–EVI relationship, as we expected EVI to improve LAI estimation. To compare the relationship of MODIS NDVI and EVI to in situ LAI, we investigated two patterns: a single relationship using all of the data and a double relationship of two periods (growing to saturation and saturation to leaf-fall). MODIS LAI was also applied directly to the model to compare its results with the others, including those of MODIS GPP. The double relationship improved the accuracy of LAI estimates over that of the single relationship. GPP derived from the double-relationship-based EVI was in best agreement with in situ GPP (r~2 > 0.8). MODIS LAI overestimated GPP values owing to overvaluations of the original LAI values. The use of MODIS products, especially EVI, has the potential to enhance the accuracy of 3-PGS. However, validation with further comparisons is still needed.