John Townshend, Ruth DeFries, Matthew Hansen, Robert Sohlberg, Charlene DiMiceli, Mark Carroll, Jessica McCarty, Karen Schleeweis, Karl Wurster, Jian Zhang
Accurate estimates of global and
regional vegetation cover are crucial for the study of biogeochemical cycles,
ecosystem assessment, and land management.
Land cover is an important driver for a variety of process models and
bounds parameters including surface roughness, standing biomass, and
evapotranspiration. Changes in
vegetative cover are equally important as they represent perturbations of the
earth system.
The
Vegetation Continuous Fields (VCF) product improves upon traditional discrete
land cover classifications by providing global sub-pixel estimates of landscape
components at a 500m spatial resolution. Estimates
are provided for percent tree cover, herbaceous cover, and bare cover.
Vegetative cover is further partitioned into leaf type (broad leaf and
needle leaf) and longevity (evergreen and deciduous).
By providing continuous percent cover estimates, users are able to define
their own vegetation class boundaries without constraints imposed by a priori
definitions inherent in discrete land cover classifications.
VCF is produced on an annual time step, allowing the analysis of changes
in vegetation density through time. Current
work is focused on increasing the spatial resolution of the VCF data set to
250m. Additional data layers are
also being developed to characterize percent crop cover and fragmentation.
The
second product in the suite is Vegetative Cover Conversion
(VCC).
This data set provides quarterly identification of land cover change hot
spots at a spatial resolution of 250m. Daily
MODIS data is assimilated to collect the best possible set of cloud free, near
nadir observations from which to assess change.
Changes of interest include deforestation, flooding, and burning.
The data set is intended to identify those areas undergoing rapid land
cover change which should be further delineated using fine resolution
observations from instruments such as Landsat and IKONOS.
Example publications: Hansen, M.C., DeFries, R.S., Townshend, J.R.G., Carroll, M., DiMiceli, C., and Sohlberg, R. 2003. Global percent tree cover at a spatial resolution of 500 meters: first results of the MODIS Vegetation Continuous Fields algorithm, Earth Interactions, 7, 1-15. Zhan, X., Sohlberg, R., Townshend, J.R.G., DiMiceli, C., Carroll, M., Eastman, J.C., Hansen, M., and DeFries, R.S. 2002. Detection of land cover changes using MODIS 250m data, Remote Sensing Environment, 83(1&2), 336-350.