Remote sensing, Principal Component Analysis, Camaquã basin
Abstract
The Camaquã basin was formed during the closing stages of the accretion of Gondwanaland. The sediments were deposited over mylonites of the Porongos Complex. Two sequences of silici-clastic sediments are present, the lower Santa Bárbara Formation and the upper Guaritas Formation, which is intruded by the Rodeio Velho calc-alkaline rocks. Relief is strongly controlled by lithology and structure, with an overall rectilinear drainage pattern. Vegetation is formed by grasses together with subordinate bushes and trees which are either scattered over the countryside or form small woods and dominates the spectral response. Soil cover is thin and rock outcrops are common, although subordinate. Based on field data, statistical parameters for atmosphere-corrected bands 2, 3, 4, 5 and 7 were set up, and served as a base for the digital processing. Greater lithological contrasts were obtained by Principal Component Analysis (PCA) through comparison of results of statistical analysis of the transformed parameters and of the original bands. A preliminary analysis of the images thus obtained led to the identification of different spectral patterns. The component PCI reflects textural patterns related to the relief and the different albedos. In PC2, the spectral response of trees highlighted the Porongos Complex and the Rodeio Velho andesites, while grasses accentuated areas of fine-grained sandstones of the Santa Bárbara and Guaritas Formations. In PC4, the sandstones and conglomerates of the two sequences, together with quartzite hills of the basement complex, are prominent.
