Seasonal changes in canopy leaf area index and MODIS vegetation products for a boreal forest site in central Finland

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 landscapelevel 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.