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