A 20-year study of NDVI variability over the Northeast Region of Brazil Barbosa, H. A. ; Huete, A. R. ; Baethgen, W. E. Abstract Publication: Journal of Arid Environments Pub Date: October 2006 DOI: 10.1016/j.jaridenv.2006.02.022 Bibcode: 2006JArEn..67..288B