Moreira, Maurício Alves, and Regina Pillis Nitzsche. “Analysis of Vegetation Indices from LANDSAT TM and SPOT XS Data”. Pesquisa Agropecuaria Brasileira, vol. 26, no. 10, Oct. 1991, pp. 1583-8, doi:10.1590/S1678-3921.pab1991.v26.3500.