Rautiainen, M; Heiskanen, J; Korhonen, L (2012). Seasonal changes in canopy leaf area index and MODIS vegetation products for a boreal forest site in central Finland. BOREAL ENVIRONMENT RESEARCH, 17(1), 72-84.
Seasonal change in leaf area index (LAI) is highly important in remote sensing of land surface phenology because LAI is a main driving factor of forest reflectance. We present a time series of in situ measurements of boreal forest LAI expanding throughout the growing period from budburst to senescence. We measured the LAI of 20 stands at approximately two-week intervals between mid-May and mid-September in 2009 in southern Finland using hemispherical photography. We compared our field reference data with landscape-level MODIS surface reflectance trajectories, vegetation indices and LAI products. Our results showed that the timing of maximum LAI varies in different forest types. In general, the MODIS-based vegetation indices followed the general trend of spring summer canopy LAI well. The MODIS LAI product, on the other hand, portrayed well the spring build-up of canopy-level foliage of broadleaved stands but began to decrease earlier in the fall than the ground reference LAI.