author = "Moura, Yhasmin Mendes de and Galv{\~a}o, L{\^e}nio Soares and 
                         Hilker, T. and Wu, J. and Saleska, S. and Amaral, C. H. do and 
                         Nelson, B. W. and Lopes, Aline Pontes and Wiedeman, K. K. and 
                         Prohaska, N. and Oliveira, R. C. and Machado, Carolyne Bueno and 
                         Arag{\~a}o, Luiz Eduardo Oliveira e Cruz de",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {University of 
                         Southampton} and {University of Arizona} and {University of 
                         Arizona} and {Universidade Federal de Vi{\c{c}}osa (UFV)} and 
                         {Instituto Nacional de Pesquisa da Amaz{\^o}nia (INPA)} and 
                         {Instituto Nacional de Pesquisas Espaciais (INPE)} and {University 
                         of Arizona} and {University of Arizona} and {Empresa Brasileira de 
                         Pesquisa Agropecu{\'a}ria (EMBRAPA)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)}",
                title = "Spectral analysis of amazon canopy phenology during the dry season 
                         using a tower hyperspectral camera and modis observations",
              journal = "ISPRS Journal of Photogrammetry and Remote Sensing",
                 year = "2017",
               volume = "131",
                pages = "52--64",
                month = "Sept.",
             keywords = "Amazon, Dry season, Hyperspectral remote sensing, Leaf flush, 
                         Phenology, Seasonality, Tropical species.",
             abstract = "The association between spectral reflectance and canopy processes 
                         remains challenging for quantifying large-scale canopy 
                         phenological cycles in tropical forests. In this study, we used a 
                         tower-mounted hyperspectral camera in an eastern Amazon forest to 
                         assess how canopy spectral signals of three species are linked 
                         with phenological processes in the 2012 dry season. We explored 
                         different approaches to disentangle the spectral components of 
                         canopy phenology processes and analyze their variations over time 
                         using 17 images acquired by the camera. The methods included 
                         linear spectral mixture analysis (SMA); principal component 
                         analysis (PCA); continuum removal (CR); and first-order derivative 
                         analysis. In addition, three vegetation indices potentially 
                         sensitive to leaf flushing, leaf loss and leaf area index (LAI) 
                         were calculated: the Enhanced Vegetation Index (EVI), Normalized 
                         Difference Vegetation Index (NDVI) and the entitled Green-Red 
                         Normalized Difference (GRND) index. We inspected also the 
                         consistency of the camera observations using Moderate Resolution 
                         Imaging Spectroradiometer (MODIS) and available phenological data 
                         on new leaf production and LAI of young, mature and old leaves 
                         simulated by a leaf demography-ontogeny model. The results showed 
                         a diversity of phenological responses during the 2012 dry season 
                         with related changes in canopy structure and greenness values. 
                         Because of the differences in timing and intensity of leaf 
                         flushing and leaf shedding, Erisma uncinatum, Manilkara huberi and 
                         Chamaecrista xinguensis presented different green vegetation (GV) 
                         and non-photosynthetic vegetation (NPV) SMA fractions; distinct 
                         PCA scores; changes in depth, width and area of the 681-nm 
                         chlorophyll absorption band; and variations over time in the EVI, 
                         GRND and NDVI. At the end of dry season, GV increased for Erisma 
                         uncinatum, while NPV increased for Chamaecrista xinguensis. For 
                         Manilkara huberi, the NPV first increased in the beginning of 
                         August and then decreased toward September with new foliage. 
                         Variations in red-edge position were not statistically significant 
                         between the species and across dates at the 95% confidence level. 
                         The camera data were affected by view-illumination effects, which 
                         reduced the SMA shade fraction over time. When MODIS data were 
                         corrected for these effects using the Multi-Angle Implementation 
                         of Atmospheric Correction Algorithm (MAIAC), we observed an EVI 
                         increase toward September that closely tracked the modeled LAI of 
                         mature leaves (35 months). Compared to the EVI, the GRND was a 
                         better indicator of leaf flushing because the modeled production 
                         of new leaves peaked in August and then declined in September 
                         following the GRND closely. While the EVI was more related to 
                         changes in mature leaf area, the GRND was more associated with new 
                         leaf flushing.",
                  doi = "10.1016/j.isprsjprs.2017.07.006",
                  url = "http://dx.doi.org/10.1016/j.isprsjprs.2017.07.006",
                 issn = "0924-2716",
             language = "en",
        urlaccessdate = "25 jan. 2021"