author = "Moreira, Luis Clenio J. and Teixeira, Adunias dos Santos and 
                         Galv{\~a}o, L{\^e}nio Soares",
          affiliation = "{Universidade Federal do Cear{\'a} (UFC)} and {Universidade 
                         Federal do Cear{\'a} (UFC)} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)}",
                title = "Laboratory salinization of Brazilian alluvial soils and the 
                         spectral effects of gypsum",
              journal = "Remote Sensing",
                 year = "2014",
               volume = "6",
               number = "4",
                pages = "2647--2663",
             keywords = "soil salinity, remote sensing, spectral reflectance, absorption 
                         bands, principal components analysis, electrical conductivity, 
                         continuum removal, band depth.",
             abstract = "Irrigation-induced salinization is an important land degradation 
                         process that affects crop yield in the Brazilian semi-arid region, 
                         and gypsum has been used as a corrective measure for saline soils. 
                         Fluvent soil samples (180) were treated with increasing levels of 
                         salinization of NaCl, MgCl2 and CaCl2. The salinity was gauged 
                         using electrical conductivity (EC). Gypsum was added to one split 
                         of these samples before they were treated by the saline solutions. 
                         Laboratory reflectance spectra were measured at nadir under a 
                         controlled environment using a FieldSpec spectrometer, a 250-W 
                         halogen lamp and a Spectralon panel. Variations in spectral 
                         reflectance and brightness were evaluated using principal 
                         component analysis, as well as the continuum-removed absorption 
                         depths of major features at 1450, 1950, 1750 and 2200 nm for both 
                         the gypsum-treated (TG) and non-treated (NTG) air-dried soil 
                         samples as a function of EC. Pearson's correlation coefficients of 
                         reflectance and the band depth with EC were also obtained to 
                         establish the relationships with salinity. Results showed that NTG 
                         samples presented a decrease in reflectance and brightness with 
                         increasing CaCl2 and MgCl2 salinization. The reverse was observed 
                         for NaCl. Gypsum increased the spectral reflectance of the soil. 
                         The best negative correlations between reflectance and EC were 
                         observed in the 1500-2400 nm range for CaCl2 and MgCl2, probably 
                         because these wavelengths are most affected by water absorption, 
                         as Ca and Mg are much more hygroscopic than Na. These decreased 
                         after chemical treatment with gypsum. The most prominent features 
                         were observed at 1450, 1950 and 1750 nm in salinized-soil spectra. 
                         The 2200-nm clay mineral absorption band depth was inversely 
                         correlated with salt concentration. From these features, only the 
                         1750 and 2200 nm ones are within atmospheric absorption windows 
                         and can be more easily measured using hyperspectral sensors.",
                  doi = "10.3390/rs6042647",
                  url = "http://dx.doi.org/10.3390/rs6042647",
                 issn = "2072-4292",
                label = "scopus 2014-05 MoreiraTeixGalv:2014:LaSaBr",
             language = "en",
           targetfile = "remotesensing-06-02647.pdf",
        urlaccessdate = "04 dez. 2020"