The Terra MODIS Vegetation Continuous Fields (VCF) product is a sub-pixel-level representation of surface vegetation cover estimates globally. Designed to continuously represent Earth's terrestrial surface as a proportion of basic vegetation traits, it provides a gradation of three surface cover components: percent tree cover, percent non-tree cover, and percent bare. VCF products provide a continuous, quantitative portrayal of land surface cover with improved spatial detail, and hence, are widely used in environmental modeling and monitoring applications.
The first generation of the VCF algorithm involved a semi-automated process to generate regression trees with machine learning software. A human operator was required to evaluate the tree and decide if it needed more or less training data inputs. The V003 VCF product is the first version from that generation, and only contains the percent tree cover layer, as does the current V005. A subsequent version will incorporate the additional two layers (i.e., percent non-tree vegetation and percent bare). Generated yearly, the VCF product is produced using monthly composites of Terra MODIS 250 and 500 meters Land Surface Reflectance data, including all seven bands, and Land Surface Temperature.
Several reasons help explain the inter-annual fluctuations in the percentage of tree cover from year to year, and therefore, users should exercise caution when considering performing inter-annual comparisons of VCF.
The VCF products are validated to stage-1; this means that their product accuracy was estimated through an assessment of the training data's accuracy, and from limited in situ field validation datasets.