Sensoriamento remoto de sistemas aquáticos e qualidade de águas superficiais da região semiárida do Brasil

Abstract

Continental waters are an important water system that must be preserved for the maintenance of life on Earth, where the Brazilian semi-arid region stands out for the considerable amount of surface reservoirs that are used to store water used for multiple purposes. The contamination of these surface waters by anthropic action, makes it urgent to adopt monitoring techniques that can assist water quality managers. Thus, remote sensing techniques have been shown to be a promising tool for the study of these systems, allowing detailed monitoring through the use of field and/or orbital data radiometric. Given the above, the hypothesis arises that the spectral features of the surface waters of the Brazilian semiarid allow to characterize, through a set of reflectance spectra, different types of water quality in terms of the concentration ranges of their Optically Active Constituents. As a way to analyze this hypothesis, this study was developed, trying to characterize, through limnological attributes and optical properties of water, the spectral behavior of the surface waters of reservoirs located in the Brazilian semiarid region.. The study was carried out in Orós dam, Trussu dam and Muquém dam in Alto Jaguaribe Basin, in State of Ceará, Brazil. Limnologiy data and spectral data were obtained at each three months, from 2012 to 2014, in these reservoirs. To correlate the limnological data and the spectral responses of water were applied the Cluster Analysis and the the Multivariate Analysis to limnological and spectral data. Results showed that according to spectral responses the water of the reservoirs were grouped in three groups. These groups showed that in rain season the water from Trussu and Muquém dams seems clear water. The water from Orós dam showed spectral response of aquatic systems water with high turbidity and chlorophyll-a. There was a good correlation between the reflectance response and the cyanobacteria density in water from Orós dam. However, the models that were developed for the estimation of cyanobacteria density using the derived by the spectral responses showed satisfactory results only for the middle third of the reservoir. The peak of reflectance representative of the presence of cyanobacteria in Orós dam presented offset to longer wavelengths in the visible range. The size of water body, the land use and the seasonality of rainfall influenced the optically active components of the water.