Leaf Area Index estimates from medium resolution satellite imagery and ground data

摘要

LAI is a key variable for describing the structure and the architecture of forest canopy and therefore of major importance for modeling the interaction between vegetation and the atmosphere. The ALPS05 project aims to investigate the 'filter effect' of Alpine forests in the environmental fate of Persistent Organic Pollutants (POPs). In 2005 ground data have been collected using the LAI-2000 instrument in representative test sites in the Gressoney Valley, Northern Italy. Data collection covered the entire vegetative period as well as senescence for three types of land cover, namely: deciduous, conifers and mixed forests. A set of MODIS 8- and 16-day composite images has been acquired over the same period and processed in order to derive Vis' (Vegetation Indices) temporal profiles. The class-specific correlation between in situ LAI measurements and NDVI, EVI (Enhanced Vegetation Index) and the Wide Dynamic Range Vegetation Index (WDRVI) have been analysed in order to define a VI-LAI relationship based on the calibration of semi-empirical regression models. The so derived VI-LAI relationships have been applied to the study area with the objective of providing a thematic map of LAI. The spatially distributed LAI values are valuable data for characterising the vegetation compartment in multimedia models describing the environmental fate of organic contaminants.