Movimentação de água salobra na laguna dos Patos/RS mediante a utilização de imagens MODIS

Abstract

Faced with a worldwide scenario of imminent scarcity of water resources, awareness of the rational use of these finite natural resources in nature is of great importance. In this context, the Patos lagoon, located in the state of Rio Grande do Sul, as a source of fresh water of great interest to adverse economic and environmental sectors, presents as a complication the insertion of salt water by the Barra dos Moles. In this juncture, the objective was to identify and estimate the space-time dynamics of the brackish water movement in the Patos lagoon, in the state of Rio Grande do Sul, through the use of remote sensing images. To do so, using the MODIS sensor, 8766 digital images were analyzed between the years 2003 to 2014. From the visual observation, 542 images were selected for the supervised classification. For this process, using the SPRING software, some water samples were created which would represent the bodies of fresh and brackish water in the Patos lagoon. The result of this operation allowed a number of years to be identified with up to 15%, others with 15% to 40%, and periods above 40% of brackish water filling in the lagoon area. Besides the quantification of the areas, it was possible to identify the seasonal dynamics of the brackish water behavior, close to the riparian municipalities. Based on the data obtained, the quantification of the number of images by the satellites Aqua and Terra revealed a potential in the availability of at least one image per month, with the exception of the months of June 2003 and August 2004. According to the results, 2005 and 2012 were the years that presented the largest dimensions of brackish area, being in some moments, over 50% of the total area. In addition, the city of São José do Norte was the most affected by the occurrence of brackish areas, presenting at least 30% of the analyzed period. Besides this city, Mostardas, Palmares do Sul and Viamão, at different times, presented areas with similar spectral behavior to the samples of the Atlantic Ocean, possibly provoked by the insertion of paleocannals near the region of Mostardas. Therefore, it was possible to conclude that it is possible to use the MODIS sensor for mapping, quantification and seasonal analysis of brackish water in the Patos lagoon, located in the state of Rio Grande do Sul.