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@Article{CarvalhoBarbNovoRudo:2015:ImScCo,
               author = "Carvalho, Lino Augusto Sander de and Barbosa, Claudio Clemente 
                         Faria and Novo, Evlyn M{\'a}rcia Le{\~a}o de Moraes and Rudorff, 
                         Conrado de Moraes",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)}",
                title = "Implications of scatter corrections for absorption measurements on 
                         optical closure of Amazon floodplain lakes using the Spectral 
                         Absorption and Attenuation Meter (AC-S-WETLabs)",
              journal = "Remote Sensing of Environment",
                 year = "2015",
               volume = "157",
                pages = "123--137",
                month = "Feb.",
             keywords = "AC-S and Hydroscat corrections, AC-S scattering correction 
                         methods, Amazon floodplain lake, Closure experiment, Inherent 
                         optical properties.",
             abstract = "Amazon floodplain lakes range widely in concentrations of 
                         optically active constituents (OAC) driven by seasonality in 
                         hydrological and biogeochemical processes, but in general they are 
                         characterized by high turbidity (NTU from 90 to 1645) compared to 
                         coastal waters. In this work, instruments for measuring inherent 
                         optical properties (IOPs) of water bodies were evaluated for the 
                         first time in floodplain lakes in the lower Amazon River during 
                         the falling limb of the hydrograph. Water column profiles of total 
                         attenuation and absorption were measured using the Spectral 
                         Absorption and Attenuation Meter (AC-S-WETLabs), and of 
                         backscattering using Hydroscat. These measurements, however, are 
                         subject to uncertainties and require corrections for turbid 
                         waters. In this paper, we assessed the implications of scattering 
                         correction methods for the absorption tube, proposed by the AC-S 
                         manufacturer, in the simulation of the Remote Sensing Reflectance 
                         (Rrs). The closure experiment comparing Hydrolight (Mobley \& 
                         Sundman, 2001) simulated Rrs and in situ Rrs demonstrated that 
                         neither of the corrections was able to thoroughly account for the 
                         scattering errors which were propagated to the absorption 
                         measurements with AC-S and backscattering with Hydroscat. The 
                         three scattering correction methods (Flat, Proportional and Kirk) 
                         either under or overestimated the absorption coefficient that 
                         resulted in either under or overestimation of the simulated Rrs. 
                         Flat and Proportional Methods resulted in an underestimation of 
                         Rrs from 400 to 550 nm and overestimation from 600 to 700 nm, 
                         indicating that the assumption of zero (0) absorption in the near 
                         infrared does not apply to inland turbid water. The Rrs errors 
                         varied also according to water OAC composition. Overall, Kirk 
                         correction method provided the best results regarding the spectral 
                         shape of the Rrs, however, failed to account for magnitude. Based 
                         on the tuning tests, the errors in spectra magnitude seem to be 
                         sensitive to the constant fraction of scattering (CFS) used in the 
                         Kirk method. Tests carried out with CFS values varying from 0.18 
                         to 0.38 indicated that magnitude error can be partially overcomed 
                         by tuning CFS according to water composition. Improvements in the 
                         scattering correction methods are required in order to obtain 
                         reliable IOPs in turbid inland Amazon lakes.",
                  doi = "10.1016/j.rse.2014.06.018",
                  url = "http://dx.doi.org/10.1016/j.rse.2014.06.018",
                 issn = "0034-4257",
             language = "en",
           targetfile = "Implications of scatter.pdf",
        urlaccessdate = "24 nov. 2020"
}


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