author = "Hilker, Thomas and Galv{\~a}o, L{\^e}nio Soares and Arag{\~a}o, 
                         Luiz Eduardo Oliveira e Cruz de and Moura, Yhasmin Mendes de and 
                         Amaral, Cibele H. do and Lyapustin, Alexei I. and Wu, Jin Wu and 
                         Albert, Loren P. and Ferreira, Marciel Jos{\'e} and Anderson, 
                         Liana O. and Santos, Victor A. H. F. dos and Prohaska, Neill and 
                         Tribuzy, Edgard and Ceron, Jo{\~a}o Vitor Barbosa and Saleska, 
                         Scott R. and Wang, Yujie and Gon{\c{c}}alves, Jos{\'e} Francisco 
                         de Carvalho and Oliveira J{\'u}nior, Raimundo Cosme de and 
                         Rodrigues, Jo{\~a}o Victor Figueiredo Cardoso and Garcia, 
                         Maquelle Neves",
          affiliation = "{University of Southampton} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)} and {Instituto Nacional de Pesquisas Espaciais 
                         (INPE)} and {Instituto Nacional de Pesquisas Espaciais (INPE)} and 
                         {Universidade Federal de Vi{\c{c}}osa (UFV)} and {NASA Goddard 
                         Space Flight Center} and {Brookhaven National Lab} and {University 
                         of Arizona} and {Universidade Federal do Amazonas (UFAM)} and 
                         {Centro Nacional de Monitoramento e Alertas de Desastres Naturais 
                         (CEMADEN)} and {Instituto Nacional de Pesquisas da Amaz{\^o}nia 
                         (INPA)} and {University of Arizona} and {Instituto Nacional de 
                         Pesquisas da Amaz{\^o}nia (INPA)} and {Instituto Nacional de 
                         Pesquisas da Amaz{\^o}nia (INPA)} and {University of Arizona} and 
                         {University of Maryland Baltimore County} and {Instituto Nacional 
                         de Pesquisas da Amaz{\^o}nia (INPA)} and {Empresa Brasileira de 
                         Pesquisa Agropecu{\'a}ria (EMBRAPA)} and {Universidade Federal do 
                         Amazonas (UFAM)} and {Instituto Nacional de Pesquisas da 
                         Amaz{\^o}nia (INPA)}",
                title = "Vegetation chlorophyll estimates in the Amazon from multi-angle 
                         MODIS observations and canopy reflectance model",
              journal = "International Journal of Applied Earth Observation and 
                 year = "2017",
               volume = "58",
                pages = "278--287",
                month = "June",
             keywords = "Chlorophyll, Phenology, Amazon, MODIS, Hyperspectral, ProSAIL, 
             abstract = "As a preparatory study for future hyperspectral missions that can 
                         measure canopy chemistry, we introduce a novel approach to 
                         investigate whether multi-angle Moderate Resolution Imaging 
                         Spectroradiometer (MODIS) data can be used to generate a 
                         preliminary database with long-term estimates of chlorophyll. 
                         MODIS monthly chlorophyll estimates between 2000 and 2015, derived 
                         from a fully coupled canopy reflectance model (ProSAIL), were 
                         inspected for consistency with eddy covariance fluxes, tower based 
                         hyperspectral images and chlorophyll measurements. MODIS 
                         chlorophyll estimates from the inverse model showed strong 
                         seasonal variations across two flux-tower sites in central and 
                         eastern Amazon. Marked increases in chlorophyll concentrations 
                         were observed during the early dry season. Remotely sensed 
                         chlorophyll concentrations were correlated to field measurements 
                         (r(2) = 0.73 and r(2) = 0.98) but the data deviated from the 1:1 
                         line with root mean square errors (RMSE) ranging from 0.355 g 
                         cm(-2) (Tapajos tower) to 0.470 g cm(-2) (Manaus tower). The 
                         chlorophyll estimates were consistent with flux tower measurements 
                         of photosynthetically active radiation (PAR) and net ecosystem 
                         productivity (NEP). We also applied ProSAIL to mono-angle 
                         hyperspectral observations from a camera installed on a tower to 
                         scale modeled chlorophyll pigments to MODIS observations (r(2) = 
                         0.73). Chlorophyll pigment concentrations (Chl(A+B)) were 
                         correlated to changes in the amount of young and mature leaf area 
                         per month (0.59 <= r(2) <= 0.64). Increases in MODIS observed 
                         Chl(A+B) were preceded by increased PAR during the dry season 
                         (0.61 <r(2) < 0.62) and followed by changes in net carbon uptake. 
                         We conclude that, at these two sites, changes in LAI, coupled with 
                         changes in leaf chlorophyll, are comparable with seasonality of 
                         plant productivity. Our results allowed the preliminary 
                         development of a 15-year time series of chlorophyll estimates over 
                         the Amazon to support canopy chemistry studies using future 
                         hyperspectral sensors.",
                  doi = "10.1016/j.jag.2017.01.014",
                  url = "http://dx.doi.org/10.1016/j.jag.2017.01.014",
                 issn = "0303-2434",
             language = "en",
           targetfile = "hilker_vegetation.pdf",
        urlaccessdate = "26 nov. 2020"