author = "Porfirio, Anthony Carlos Silva and Ceballos, Juan Carlos",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)}",
                title = "A method for estimating direct normal irradiation from GOES 
                         geostationary satellite imagery: Validation and application over 
                         Northeast Brazil",
              journal = "Solar Energy",
                 year = "2017",
               volume = "155",
                pages = "178--190",
                month = "Oct.",
             keywords = "Solar radiation, Direct normal irradiance, Satellite data, 
                         Satellite-derived DNI.",
             abstract = "The mapping and monitoring of Direct Normal Irradiance (DNI) is 
                         most relevant for the proper installation of solar power plants 
                         that use concentrating solar systems. This paper presents a 
                         satellite-based method for estimating DNI and daily direct normal 
                         irradiation (Qn) that uses a minimal set of regional 
                         meteorological information and avoids empirical adjustment with 
                         ground-based radiometric data. The focus of the validation and 
                         application were on the Northeast Brazil region (NEB), which 
                         exhibits high solar radiation levels throughout the year. Two 
                         basic parameters for satellite-derived DNI estimates are: (i) DNI 
                         under clear-sky conditions DNIclear (computed from the REST model) 
                         and (ii) cloud cover C (estimated from GOES visible imagery). The 
                         first validations were performed by comparison with measurements 
                         from three radiometric stations of the SONDA network in the NEB 
                         (Petrolina, Natal and S{\~a}o Lu{\'{\i}}s) during 20072008. 
                         Overall, the results confirmed the good performance of the 
                         proposed model. DNI daily cycles in conditions of clear and 
                         partially cloudy skies were represented satisfactorily, with daily 
                         average errors within 25 W m\−2. Good linearity was found 
                         between the measured and satellite-estimated Qn, with coefficients 
                         of determination (R2) ranging from 0.84 to 0.89. The average 
                         values of MBE (Mean Bias Error) and RMSE (Root Mean Square Error) 
                         over all sites were \−1.7% and 18.7%, respectively. In 
                         addition, seasonal and annual average maps of direct normal 
                         irradiation were generated over NEB for 2008. It was found that 
                         the spatialtemporal variability of Qn is strongly modulated by 
                         meteorological systems acting in the region, such as the ITCZ 
                         (Intertropical Convergence Zone). The mapped results reveal that 
                         the highest value was approximately 22 MJ m\−2 on an annual 
                         average basis, and higher values occurred in areas of semi-arid 
                         climate. The proposed satellite-based model may be applied for 
                         providing information of DNI (with a spatial resolution of 4 km), 
                         particularly over regions without in situ measurements, and 
                         suggests good accuracy for climatic and solar resource studies.",
                  doi = "10.1016/j.solener.2017.05.096",
                  url = "http://dx.doi.org/10.1016/j.solener.2017.05.096",
                 issn = "0038-092X",
             language = "en",
           targetfile = "porfirio.pdf",
        urlaccessdate = "28 nov. 2020"