Background and Context
The origins of BigFoot are traceable to 1992 when S. Running of MODLand
contacted the Long-Term Ecological Research (LTER) community to assist
with validation of anticipated MODIS products. The first proposal, funded
by NASA's Terrestrial Ecology Program (TEP) in 1994, involved prototype
scaling exercises using existing data at 14 (mostly LTER) sites. In
1996, the 20+ person team held an LTER-funded workshop to share results
and stratagies for future direction. Workshop proceedings were published
in a special issue of Remote Sensing of Environment in October 1999,
edited by Cohen and Justice. In 1998, the largely amorphous project
was rescoped, and with renewed TEP support became what we now call BigFoot.
What defines the project is its focus on using remote sensing and ecosystem
process models to scale ecological field measurements within a greater
eddy flux tower footprint. Doing this across a range of biomes using
standardized measurements and an innovative sampling design affords
us a unique opportunity to examine ecosystem function at the local level
in a global context.
Originally, BigFoot included four sites, with the first field season
being in 1999 at two of these sites (see group 1 in field activity schedule
below). Each site represents a distinct and globally important biome.
The NOBS site (or Northern Old Black Spuce site from BOREAS) is a boreal
needleleaf evergreen forest. HARV, (the Harvard Forest LTER site) is
a temperate mixed forest. The agricultural cropland site, AGRO (a.k.a.
Bondville) is primarily corn and soybeans. KONZ (the Konza Prairie LTER
site) is a tallgrass prairie. The project focused on validation of MODIS
land cover, LAI, and NPP products.
The overall goal of BigFoot is to continue with MODIS land cover, LAI,
and NPP product validation at the four existing sites, but now we have
expanded our focus to include validation of fAPAR
and our biome coverage to include five new sites for a more globally
comprehensive assessment of MODIS product validity (see field activity
schedule above). The new sites include a desert grassland (SEVI, the
Sevilleta LTER), an tundra near the Arctic coastal plain (TUND, near
Barrow, AK), and a tropical broadleaf evergreen forest in the Amazon
Basin (TAPA, the Tapajos Primary Forest site of LBA). In addition, we
offer two sites at no additional cost to NASA (Group 3); these sites
include a second temperate mixed forest (CHEQ, Chequamegon National
Forest in Wisconsin), and a temperate needleleaf evergreen forest near
Metolius, Oregon (METL). The Group 3 sites are fully funded by either
the NASA EOS Validation Program (CHEQ to Gower) or the Environmental
Protection Agency (METL to B. Law, Turner, Cohen et al.). Continued
work at NOBS beyond 2000 is funded by the National Science Foundation
to Gower. Another important goal of BigFoot is to explicitly assess
if MODLand products can detect the effects of inter-annual variation
in climate on vegetation cover, LAI, fAPAR,
and NPP. Also, we examine how LUE varies within and among sites and
vegetation types and propose to actively facilitate further formation
and definition of GTOS in support of MODIS validation.
In addition to BigFoot, there are several other initiatives addressing
the development of a global terrestrial monitoring and validation program.
These include the Global Primary Production Data Initiative (GPPDI),
the worldwide CO2 flux network (FLUXNET),
the MODLand Science Team and associated validation program, the Vegetation/Ecosystem
Modeling and Analysis Project (VEMAP), and the Global Analysis, Integration,
and Modeling (GAIM) NPP model intercomparison activity. These all recognize
the need to consider several key elements in the formation of a global
terrestrial monitoring system, including: in situ vegetation
measurements, eddy flux tower measurements, vegetation surfaces derived
from remote sensing, and biogeochemical process models, all used over
time. However, these programs exist either as stand alone efforts (e.g.,
FLUXNET, MODIS-NPP modeling) or incorporate only one or two of the key
elements of a comprehensive observation and validation program (e.g.,
GPPDI, VEMAP). In contrast, BigFoot integrates all of the aforementioned
key elements at a spatial scale that serves as a rigorous validation
of global sensor and terrestrial modeling products (as shown in the
- Uses field measurements and Landsat ETM+ data to parameterize eocsystem process
models at a local scale (i.e., within the 5 x 5 km BigFoot footprint) so that we can
understand the environmental and ecological controls on carbon exchange between
terrestrial ecosystems and the atmosphere at that scale.
- Assesses how accurately process models capture the environmental controls on
CO2 and H2O
exchange between terrestrial ecosystems and the atmosphere.
- Statistically compares the land cover, LAI, fAPAR,
and NPP surfaces we generate against field measurements to help establish
the accuracy of those surfaces, so that they can be legitimately compared
gainst co-located sections of globally-derived, generalized surfaces
(such as those of MODLand).
- Compares BigFoot modeled GPP (gross primary production) against calculations
of GPP from flux tower data–a strong first step towards effective integration of
process models and flux measurements.
- Provides both field-based and map-based characterizations of flux tower