National Land Cover Database 2011 - Tree Canopy (NLCD2011)

References

Coulston, J. W., Moisen, Gretchen G., Wilson, B. T., Finco, M. V., Cohen, W. B., and C.K. Brewer, 2012.  Modeling percent tree canopy cover: a pilot study.   Photogrammetric Engineering & Remote Sensing 78(7): 715–727.