Taking into account the importance of mangrove environments for the biodiversity of coastal areas, the objective of this paper is to classify the different types of irregular human occupation on the areas of mangrove vegetation in São Luis, capital of Maranhão State, Brazil, considering the OBIA (Object-based Image Analysis) approach with WorldView-2 satellite data and using InterIMAGE, a free image analysis software. A methodology for the study of the area covered by mangroves at the northern portion of the city was proposed to identify the main targets of this area, such as: marsh areas (known locally as Apicum), mangrove forests, tidal channels, blockhouses (irregular constructions), embankments, paved streets and different condominiums. Initially a databank including information on the main types of occupation and environments was established for the area under study. An image fusion (multispectral bands with panchromatic band) was done, to improve the information content of WorldView-2 data. Following an ortho-rectification was made with the dataset used, in order to compare with cartographical data from the municipality, using Ground Control Points (GCPs) collected during field survey. Using the data mining software GEODMA, a series of attributes which characterize the targets of interest was established. Afterwards the classes were structured, a knowledge model was created and the classification performed. The OBIA approach eased mapping of such sensitive areas, showing the irregular occupations and embankments of mangrove forests, reducing its area and damaging the marine biodiversity.
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ABSTRACT:The objective of this study is to verify the contribution of the spectral bands from the new WorldView-2 satellite for the extraction of urban targets aiming a detailed mapping from the city of São Luis, at the coastal zone of Maranhão State, Brazil. This satellite system has 3 bands in the visible portion of the spectrum and also the following 4 new bands: Coastal (400-450 nm), Yellow (585-625 nm), Red Edge (705-745 nm), and Near Infrared 2 (860-1040 nm). As for the methodology used, initially a fusion was made among the panchromatic and the multispectral bands, combining the spectral information of the multispectral bands with the geometric information of the panchromatic band. Following the ortho-rectification of the dataset was done, using ground control points (GCPs) obtained during field survey. The classification reached high values of Kappa indices. The use of the new bands Red Edge and Near Infrared 2, allowed the improvement of discriminations at tidal flats, mangrove and other vegetation types. The Yellow band improved the discrimination of bare soils -very important information for urban planning -and ceramic roofs. The Coastal band allowed to map the tidal channels which cross the urban area of São Luis, a typical feature of this coastal area. The functionalities of software GEODMA used, allowed an efficient attribute selection which improved the land cover classification from the test sites. The new WorldView-2 bands permit the identification and extraction of the features mentioned, because these bands are positioned at important parts of the electromagnetic spectrum, such as band Red Edge, which strongly improves the discrimination of vegetation conditions. Combining both higher spatial and spectral resolutions, WorldView-2 data allows an improvement on the discrimination of physical characteristics of the targets of interest, thus permitting a higher precision of land use/land cover maps, contributing to urban planning. The test sites of this study represent the main problem areas involving the city of São Luis and the entire region of the Maranhão Island.
As áreas urbanas caracterizam-se por ser um espaço em transformação. Quando estão localizadas em ambientes costeiros, tornam-se ainda mais frágeis pela presença de ecossistemas como os manguezais e as dunas. Para o processamento e a avaliação de dados dos novos sensores orbitais utiliza-se o paradigma de GEOBIA. Neste trabalho foram usadas imagens do satélite WorldView-II de alta resolução espacial com 0,50m de resolução e oito bandas multiespectrais. O objetivo deste estudo foi avaliar a capacidade do uso dessas imagens aliadas a técnicas de mineração de dados, para a classificação da cobertura do solo urbano em áreas urbanas costeiras. Os testes foram realizados em duas áreas-piloto no setor norte da cidade de São Luís - MA (Ilha do Maranhão). Inicialmente foram realizados testes com um modelo de classificação para as áreas-piloto, considerando somente uma análise exploratória a partir das ferramentas implementadas no software InterIMAGE (Teste AI e BI). Para efeito de comparação, foi elaborado um modelo de conhecimento que, com base nos resultados da mineração de dados por árvore de decisão com um número mínimo de folhas, indicava os melhores limiares e atributos para classificar as imagens. Este modelo foi adaptado a concepção do software InterIMAGE (Teste AII e BII). Através de avaliações estatísticas foi possível optar pelas classificações com maior precisão que obtiveram índices Kappa de 0,8354 (teste AII) e 0,8446 (teste BII). Desta forma foi possível customizar os atributos anteriormente validados na classificação de cobertura da terra, obtendo-se índices Kappade 0,7924 para área A e 0,7631 para área B.
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