TY - JOUR
T1 - Vegetation chlorophyll estimates in the Amazon from multi-angle MODIS observations and canopy reflectance model
AU - Hilker, Thomas
AU - Galvão, Lênio Soares
AU - Aragão, Luiz E.O.C.
AU - de Moura, Yhasmin M.
AU - do Amaral, Cibele H.
AU - Lyapustin, Alexei I.
AU - Wu, Jin
AU - Albert, Loren P.
AU - Ferreira, Marciel José
AU - Anderson, Liana O.
AU - dos Santos, Victor A.H.F.
AU - Prohaska, Neill
AU - Tribuzy, Edgard
AU - Barbosa Ceron, João Vitor
AU - Saleska, Scott R.
AU - Wang, Yujie
AU - de Carvalho Gonçalves, José Francisco
AU - de Oliveira Junior, Raimundo Cosme
AU - Cardoso Rodrigues, João Victor Figueiredo
AU - Garcia, Maquelle Neves
N1 - Funding Information:
This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (grant number PVE 401025/2014-4 ); and the GOAmazon project, funded jointly by U.S. Department of Energy (DOE) ( DE-SC0008383 ), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) , and Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM) ( 062.00570/2014 ). JMM was supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) ( 12881-13-9 ). CHA was supported by FAPESP ( 15/05923-5 ).
Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2017/6
Y1 - 2017/6
N2 - 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 (r2 = 0.73 and r2 = 0.98) but the data deviated from the 1:1 line with root mean square errors (RMSE) ranging from 0.355 μg cm−2 (Tapajós tower) to 0.470 μg 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 (r2 = 0.73). Chlorophyll pigment concentrations (ChlA+B) were correlated to changes in the amount of young and mature leaf area per month (0.59 ≤ r2 ≤ 0.64). Increases in MODIS observed ChlA+B were preceded by increased PAR during the dry season (0.61 ≤ r2 ≤ 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.
AB - 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 (r2 = 0.73 and r2 = 0.98) but the data deviated from the 1:1 line with root mean square errors (RMSE) ranging from 0.355 μg cm−2 (Tapajós tower) to 0.470 μg 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 (r2 = 0.73). Chlorophyll pigment concentrations (ChlA+B) were correlated to changes in the amount of young and mature leaf area per month (0.59 ≤ r2 ≤ 0.64). Increases in MODIS observed ChlA+B were preceded by increased PAR during the dry season (0.61 ≤ r2 ≤ 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.
KW - Amazon
KW - Chlorophyll
KW - Hyperspectral
KW - MODIS
KW - Multi-angular
KW - Phenology
KW - ProSAIL
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U2 - 10.1016/j.jag.2017.01.014
DO - 10.1016/j.jag.2017.01.014
M3 - Article
AN - SCOPUS:85041777692
SN - 1569-8432
VL - 58
SP - 278
EP - 287
JO - International Journal of Applied Earth Observation and Geoinformation
JF - International Journal of Applied Earth Observation and Geoinformation
ER -