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Instituto Nacional de Pesquisas Espaciais (INPE) (2007)

Avaliação da desertificação no sudoeste do estado do Piauí, através de técnicas de sensoriamento remoto

Monteiro de Carvalho Carolina

Titre : Avaliação da desertificação no sudoeste do estado do Piauí, através de técnicas de sensoriamento remoto

Auteur : Carolina Monteiro de Carvalho

Université de soutenance : Instituto Nacional de Pesquisas Espaciais (INPE) Brazil

Grade  : Mestrado do Curso em Sensoriamento Remoto 2007

Résumé
Traditional agricultural practices of vegetation burning and exhaustive diamond exploration have been responsible for a desertification process in the region defined by the towns of Gilbués, Barreiras do Piauí, Monte Alegre do Piauí e São Gonçalo do Gurguéia in the south of the Piauí State, northeastern Brazil. This area is located in the transition zone between the domains of the savanna (cerrado) vegetation and the caatinga vegetation. Landsat TM (Thematic Mapper) images acquired in 1986, 1994, 2001 and 2005 during the dry and rainy seasons were used to estimate the extent of the the desertification process in that region. A linear spectral mixture modeling was applied over the image set to produce three fraction images : soil, vegetation, and shade. Afterwards, a segmentation algorithm was applied to the soil- fraction images, followed by unsupervised region classification (ISOSEG) and map editing techniques. The editing phase consisted of a visual inspection directly on the monitor correcting commission and omission errors in classified areas. Three classes of land use/land cover were mapped : bare soil, degraded cerrado/caatinga vegetation, and cerrado/caatinga vegetation. Final thematic maps were analysed taking into account pluviometric data, allowing identifying a subtle transition between classes from a season to another at all considered years. Due to this, bare soil extension values were considered only for the scenes acquired in the rainy season. In spite of certain variation on the dynamic of the vegetation cover controlled by the seasons, calculate values of bare soil areas indicated positive increment in desertification over time. However, because only a few numbers of images was available, it was not possible to estimate an annual rate of the desertification process in the region, as well as to forecast the advance of this process over the next coming years.

Présentation

Page publiée le 30 mars 2010, mise à jour le 12 septembre 2018