Variation of MODIS Reflectance and Vegetation Indices with Viewing Geometry and Soybean Development

Autor(es)

Breunig, Fabio M. ^[1] ; Galvao, Lenio S. ^[1] ; Formaggio, Antonio R. ^[1] ; Epiphanio, Jose C. N. ^[1]

Afiliação do(s) autor(es)

^[1] Inst Nacl Pesquisas Espaciais, Div Sensoriamento Remoto, BR-12245970 Sao Jose Dos Campos, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Anais da Academia Brasileira de Ciências; v. 84, n. 2, p. 263-274, JUN 2012.
• Citações Web of Science: 1

Resumo

Directional effects introduce a variability in reflectance and vegetation index determination, especially when large field-of-view sensors are used (e.g., Moderate Resolution Imaging Spectroradiometer - MODIS). In this study, we evaluated directional effects on MODIS reflectance and four vegetation indices (Normalized Difference Vegetation Index - NDVI; Enhanced Vegetation Index - EVI; Normalized Difference Water Index - NDWI1640 and NDWI2120) with the soybean development in two growing seasons (2004-2005 and 2005-2006). To keep the reproductive stage for a given cultivar as a constant factor while varying viewing geometry, pairs of images obtained in close dates and opposite view angles were analyzed. By using a non-parametric statistics with bootstrapping and by normalizing these indices for angular differences among viewing directions, their sensitivities to directional effects were studied. Results showed that the variation in MODIS reflectance between consecutive phenological stages was generally smaller than that resultant from viewing geometry for closed canopies. The contrary was observed for incomplete canopies. The reflectance of the first seven MODIS bands was higher in the backscattering. Except for the EVI. the other. vegetation indices had larger values in the forward scattering direction. Directional effects decreased:with-canopy closure. The NDVI was lesser affected by directional effects than the other indices, presenting the smallest differences between viewing directions for fixed phenological stages. (AU)

• Processo FAPESP: 08/11499-8 - Dinâmica espectral-angular de variedades de soja e relações com produtividade a partir de dados off-nadir MODIS, ALI e Hyperion
• Beneficiário: Lenio Soares Galvão
• Modalidade de apoio: Auxílio à Pesquisa - Regular