author = "Maeda, Eduardo Eiji and Galv{\~a}o, L{\^e}nio Soares",
          affiliation = "{University of Helsink} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)}",
                title = "Sun-sensor geometry effects on vegetation index anomalies in the 
                         Amazon rainforest",
              journal = "GIScience and Remote Sensing",
                 year = "2015",
               volume = "52",
               number = "3",
                pages = "332--343",
             keywords = "bidirectional effects, MODIS, view-illumination effects, 
                         viewing-illumination geometry, Vegetation Indices, Amazon.",
             abstract = "The capacity of orbital sensors to monitor vegetation functioning 
                         and phenology in the Amazon rainforest using vegetation indices 
                         (VIs) has been broadly challenged in recent years. In particular, 
                         recent studies indicate that artifacts associated with sun-sensor 
                         geometry are likely to have major influence on the variability of 
                         some VIs. Nevertheless, the magnitude of this influence and the 
                         impacts on different VIs are still poorly understood. This study 
                         evaluates the scaling and magnitude of the phase angle variation 
                         effects on six different VIs, as well as in the individual 
                         spectral bands used for computing these indices. Our results show 
                         a significant and consistent relationship between phase angle and 
                         VI anomalies. The scaling (i.e. the change rate of VI anomaly with 
                         phase angle) of this relationship varies according to spectral 
                         bands and VIs. Median anomalies in individual Moderate Resolution 
                         Imaging Spectroradiometer (MODIS) bands showed a variation of up 
                         to \−0.045 degree\−1 , while median VI anomaly 
                         variations reached \−0.047 degree\−1 . The scaling 
                         of all relationships was shown to be constant throughout the year. 
                         Average phase angle values in the Amazon basin ranged from 
                         approximately 25 degrees in October to 41 degrees in June. Such 
                         variation can, on average, cause changes of up to 0.75 in some 
                         VIs, therefore having major impacts on the interpretation of the 
                         relationships between VIs and forest phenology.",
                  doi = "10.1080/15481603.2015.1038428",
                  url = "http://dx.doi.org/10.1080/15481603.2015.1038428",
                 issn = "1548-1603",
                label = "lattes: 5507769922001047 2 MaedaGalv:2015:SuGeEf",
             language = "en",
        urlaccessdate = "26 nov. 2020"