Related to the carbon cycle, MODIS science teams routinely develop a variety of global surfaces such as land cover, leaf area index (LAI), and net primary production (NPP) using MODIS data and functional algorithms. The quality of these surfaces must be evaluated to determine their effectiveness for global biosphere monitoring. A project called BigFoot in coordination with the GTOS NPP project is an organized effort across nine sites, representing different biomes. At each site, field measurements of ecosystem properties are made, the measurements are integrated with Landsat imagery and models to produce surfaces of land cover, LAI, and NPP, and then these surfaces are compared to MODIS-derived surfaces. Each site has an eddy-covariance flux tower that measures water vapor and CO2 fluxes. Flux tower foot-prints are relatively small, approximately 1 km2. BigFoot characte-rizes 25 km2 around each tower. The field sampling design is a nested spatial series to facilitate geostatistical analyses. Field data are used both to develop site-specific algorithms for mapping/modeling the variables of interest and to characterize the errors in derived BigFoot surfaces.

MODIS surface data of scientific quality are just beginning to be produced, so no official comparisons of BigFoot and MODIS surfaces have been completed.

However, BigFoot has completed its analyses over four sites. This preliminary work suggests that ecosystem carbon allocation varies among land cover classes that are finer than those resolved by MODIS. For example, MODIS labels both corn and soybeans as croplands, but these two crops absorb and utilize radiation differently, in ways that are important to NPP. The level of error is dependent on the distribution and proportion of each crop in the study area. Multiple year measurements are also necessary as research by BigFoot and FLUXNET have shown that carbon dynamics varies interannually.

The nine BigFoot sites will complete their analyses and comparisons with MODIS products over the next three years. With input from BigFoot and similar efforts globally, MODIS-derived products should gain credibility and begin to serve as a critical component of an integrated global biosphere monitoring system.

Further details on BigFOOT