The objective of BigFoot is provide ground validation of MODLand (MODIS Land Science Team) land cover, leaf area index (LAI), fAPAR, and net primary production (NPP) products. The name BigFoot was selected to describe the multiple scales, or footprints, of ground validation that the project will undertake (Figure 1). The current BigFoot study plan covers measurement, mapping, and modeling activities at 4 sites, each equipped with a meteorological flux tower which makes continuous measurements of energy, water, and carbon fluxes for a roughly a 1 km2 footprint. Ground validation measurements will be conducted both within the 1 km2 eddy flux tower footprint and in an outlying area covering 25 km2.

A total of four sites were selected for the BigFoot study: a boreal forest (NOBS), a temperate hardwood forest (HARV), an agriculture cropland (AGRO), and tallgrass prairie grassland (KONZ). The boreal evergreen conifer forest site is the BOREAS NSA old black spruce site near Thompson, Manitoba Canada. The temperate crop site has alternate crops of corn and soybean; it is located near Champaign-Urbana, Illinois. The site is also used for GEWEX validation. The tallgrass prairie site is located at Konza Prairie near Manhattan, Kansas. The site is part of the U.S. Long-Term Ecological Research (LTER) network. The temperate hardwood forest site is located at the Harvard Forest, near Petersham, MA and is also part of the U.S. LTER network. LTER site.

The core BigFoot products will be 25 km2 surfaces at 25 m spatial resolution for land cover, LAI, fAPAR, and NPP. Land cover and LAI will be based on Landsat ETM+ imagery, and NPP will be based on spatially distributed, process-based biogeochemistry models. The models will be initialized with the land cover and LAI surfaces and driven by time-series meteorological data. Validation of BigFoot land cover and LAI surfaces will be based on ground sampling of land cover and LAI which is not used in development of the original surfaces. Validation of BigFoot carbon and water flux estimates will be made over the flux tower footprints at a daily time step, based on flux tower measurements, and for the 5x5km study area (i.e., henceforth referred to as the MODLand footprint) based on a sample of new aboveground NPP (NPPA) measurements. Belowground NPP (NPPB) will be measured mostly in the immediate vicinity of the flux towers.

For comparisons to MODLand NPP products, the BigFoot 25 m2 grid at each site will be overlain with the 1 km2 MODLand grid that is spatially consistent with the MODIS imagery. NPP models will be run for calendar years 1999 and 2000 for the boreal forest (NOBS) and agroecosystem (AGRO) study area, and compared to MODLand NPP products produced at eight-day and annual time steps (Figure 2). Similar analyses will be conducted for the tallgrass prairie (KONZ) and temperate forest (HARV) study area in 200 and 2001. Differences between BigFoot and MODLand NPP products will be evaluated in terms of the differences in spatial resolution of the analysis, the differences in vegetation classification system, and the differences in epsilon, the light use efficiency factor, as used in the MODLand NPP algorithm and as derived from BigFoot NPP simulations.

Publications
Gower, S.T., C.J. Kucharik and J.M. Norman. 1999. Direct and indirect estimation of leaf area index, fapar, and net primary production of terrestrial ecosystems. Remote Sensing of Environment 70:29-51.

Running, S.W., D.D. Baldochii, W. Cohen, S.T. Gower, D. Turner, P. Bakwin, K. Hibbard. 1999. A global terrestrial monitoring network, scaling tower fluxes with ecosystem modeling and EOS satellite data. Remote Sensing of Environment 70:108-127.

Canadell, J.G., H.A. Mooney, D.D. Baldochi, J.A. Berry, J.R. Ehleringer, C.B. Field, S.T. Gower, D.Y. Hollinger, J.E. Hunt, R.B. Jackson, S.W. Running, G.R. Shaver, W. Steffen, S.E. Trumbore, R. Valentini, and B.Y. Bond. 1999. Carbon metabolism of the terrestrial biosphere: A multi-technique approach for improved understanding. Ecosystems 3:115-130.