@Article{CerqueiraJúniorFerHoeLemSou:2014:LaMeAp,
               author = "Cerqueira J{\'u}nior, Jo{\~a}o Gualberto de and Fernandez, J. H. 
                         and Hoelzemann, J. J. and Leme, Neusa Maria Paes and Sousa, C. 
                         T.",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and Univ Fed 
                         Rio Grande Norte UFRN, BR-59078970 Natal, RN, Brazil. and Univ Fed 
                         Rio Grande Norte UFRN, BR-59078970 Natal, RN, Brazil. and 
                         {Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)}",
                title = "Langley method applied in study of aerosol optical depth in the 
                         Brazilian semiarid region using 500, 670 and 870 nm bands for sun 
                         photometer calibration",
              journal = "Advances in Space Research",
                 year = "2014",
               volume = "54",
               number = "8",
                pages = "1530--1543",
                month = "Oct.",
             keywords = "optical depth, Brazilian semiarid, sun photometer calibration, 
                         Langley method.",
             abstract = "Due to the high costs of commercial monitoring instruments, a 
                         portable sun photometer was developed at INPE/CRN laboratories, 
                         operating in four bands, with two bands in the visible spectrum 
                         and two in near infrared. The instrument calibration process is 
                         performed by applying the classical Langley method. Application of 
                         the Langley's methodology requires a site with high optical 
                         stability during the measurements, which is usually found in high 
                         altitudes. However, far from being an ideal site, Harrison et al. 
                         (1994) report success with applying the Langley method to some 
                         data for a site in Boulder, Colorado. Recently, Liu et al. (2011) 
                         show that low elevation sites, far away from urban and industrial 
                         centers can provide a stable optical depth, similar to high 
                         altitudes. In this study we investigated the feasibility of 
                         applying the methodology in the semiarid region of northeastern 
                         Brazil, far away from pollution areas with low altitudes, for sun 
                         photometer calibration. We investigated optical depth stability 
                         using two periods of measurements in the year during dry season in 
                         austral summer. The first one was in December when the native 
                         vegetation naturally dries, losing all its leaves and the second 
                         one was in September in the middle of the dry season when the 
                         vegetation is still with leaves. The data were distributed during 
                         four days in December 2012 and four days in September 2013 
                         totaling eleven half days of collections between mornings and 
                         afternoons and by means of fitted line to the data V-0 values were 
                         found. Despite the high correlation between the collected data and 
                         the fitted line, the study showed a variation between the values 
                         of V-0 greater than allowed for sun photometer calibration. The 
                         lowest V-0 variation reached in this experiment with values lower 
                         than 3\% for the bands 500, 670 and 870 nm are displayed in 
                         tables. The results indicate that the site needs to be better 
                         characterized with studies in more favorable periods, soon after 
                         the rainy season.",
                  doi = "10.1016/j.asr.2014.06.006",
                  url = "http://dx.doi.org/10.1016/j.asr.2014.06.006",
                 issn = "0273-1177 and 1879-1948",
                label = "isi 2015-01 FernandezHoeLemSou:2014:LaMeAp",
             language = "en",
           targetfile = "1-s2.0-S0273117714003482-main.pdf",
        urlaccessdate = "24 abr. 2024"
}