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@Article{LuizMartCostPere:2018:CaSt,
               author = "Luiz, Eduardo Weide and Martins, Fernando Ramos and Costa, Rodrigo 
                         Santos and Pereira, Enio Bueno",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and 
                         {Universidade Federal de S{\~a}o Paulo (UNIFESP)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)}",
                title = "Comparison of methodologies for cloud cover estimation in Brazil: 
                         a case study",
              journal = "Energy for Sustainable Development",
                 year = "2018",
               volume = "43",
                pages = "15--22",
                month = "mar.",
             keywords = "Cloud cover estimation, All-sky camera, Satellite, Long-wave 
                         radiation.",
             abstract = "Clouds are the major modulator of the shortwave and longwave 
                         radiation components of the Earth's energy balance and, as such, 
                         help to regulate the planet's temperature. In the energy sector, 
                         clouds are a source of instability in the generation of energy 
                         using solar technologies. This study aims at comparing three 
                         approaches to get cloud cover information in the Southeastern 
                         region of Brazil during the period of approximately three months. 
                         The first method, assumed as reference, uses all-sky camera 
                         pictures for the cloud cover estimation. The other two 
                         methodologies use downward longwave radiation with surface 
                         meteorological data and geostationary satellite data. Both methods 
                         presented good agreement with the camera for clear sky and 
                         overcast conditions, with probabilities of detection of 92.8% and 
                         80.7% for the longwave method and 93.3% and 87.6% for the 
                         satellite method, respectively. The major problem occurs with the 
                         broken-clouds sky scenario, with probabilities of detection above 
                         38%, where each method has its own specificity, such as, longwave 
                         emissivity of the atmosphere, spatial resolution and view 
                         geometry. The long-wave method has the minor R correlation with 
                         the camera (87%) when compared with the satellite method (93%) and 
                         requires a daily normalization, which make it not usable for 
                         instantaneous measurements. Regarding the satellite method, the 
                         most important issue is the spatial resolution, which has the 
                         major impact on the broken-clouds sky scenarios. The cloud masking 
                         works properly for large clouds with, at least, the size 
                         comparable to the satellite image pixel. Furthermore, the method 
                         using the all-sky camera also needs to be improved, because it 
                         presented some deficiencies, like very bright areas around the 
                         sun, sometimes identified as clouds, leading to cloud cover 
                         overestimation.",
                  doi = "10.1016/j.esd.2017.12.001",
                  url = "http://dx.doi.org/10.1016/j.esd.2017.12.001",
                 issn = "0973-0826",
             language = "en",
        urlaccessdate = "25 nov. 2020"
}


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