Assessment of MODIS Leaf Area Index Product in Alaska

Dave Verbyla

The MODIS Leaf Area Index (LAI) Product is a global product produced every 8 days. The Leaf Area Index is estimated by a radiative transfer model assuming a given distribution of biome types within each pixel. The LAI Product was evaluated for the period of May 2002 to September 2002. The temporal pattern of spring greenup and fall senescence appeared reasonable across a large latitudinal transect from the Kenai Peninsula to the Arctic Coastal Plain. The temporal pattern also appeared reasonable across an elevational transect from Bonanza Creek Experimental Forest to Caribou Poker Creek Research Watershed to Eagle Summit. The positional accuracy and spatial pattern LAI was judged excellent by comparing the M2002 maximum LAI for the Survey Line Burn with a Landsat ETM+ image. However, there were two consistent problems with the LAI index at all spatial scales. First, a dip in maximum LAI during the green-up period most likely indicated cloud contamination of pixels. Second, the maximum 2002 LAI estimate was unrealistically high (>6.5) in many areas of Alaska.