Castro, Paulo

Ferreira, Narciso

Godinho, M.

Neves, L.

Pereira, A.

Venâncio, P.

Laboratório Nacional de Energia e Geologia Repository

Remote sensing applied to geological mapping and tectonics : a study in the Viseu region, Central Portugal

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Geophysical Research Abstracts,Vol. 10, EGU2008-A-05682, 2008SRef-ID: 1607-7962/gra/EGU2008-A-05682EGU General Assembly 2008© Author(s) 2008Remote sensing applied to geological mapping andtectonics: a study in the Viseu region (Central Portugal)A. Pereira (1,2), P. Venâncio (1), L. Neves (1,2), M. Godinho (1), N. Ferreira (3) andP. Castro (3)(1) Department of Earth Sciences, University of Coimbra, Portugal, (2) IMAR-CIC, Coimbra,Portugal, (3) INETI, Department of Geology, S. Mamede de Infesta, Portugal.(apereira@dct.uc.pt)Geological mapping at a detailed scale of the Viseu region (Central Portugal) hasbeen developed since the seventies by several authors, and it is partially published;unpublished areas have been already object of preliminary field work. The region islargely dominated by Hercynian granitic rocks (80%), which can be broadly dividedin two main series: syn- to late-orogenic muscovite-biotite granites (MBG) and late-orogenic porphyritic biotite granites (PBG). Small outcrops of gabbro to granodioriterocks can also be found. Schists and graywackes of pre-Ordovician age (CXG) arealso present (12%), sometimes with amphibolite intercalations. Cenozoic sedimentsand alluvium deposits correspond to the remaing 8% of the area.With the goal of completing the 17-A geological map of the 1:50.000 national gridwith 160 km2 (Viseu), an integration of the available information was carried outthrough GIS techniques; it become immediately apparent that important differencesof criteria have been used through time by different authors, specially in what con-cerns fault pattern recognition. The purpose of the present work was to evaluate theeffectiveness of remote sensing techniques in order to improve the harmonization ofthe cartographic information, as well as to reconstruct the most dominant tectonic fea-tures of the region with unique criteria. For this objective, optical and microwave data,collected from sensors onboard of Landsat 7 ETM+ and ENVISAT (ASAR) satellites,was used. Digital elevation models build from topographic maps supported the ge-ometric correction of satellite images and were also used in the structural lineamentanalysis. All images were georeferenced to UTM projection with good results and lowquadratic deviations. Optical data was enhanced through RGB, HSI and Tasseled captransforms, as well as principal component analysis. Besides the use of the elevationdata, lineament analysis was also performed on the basis of the application of direc-tional filters on the optical data (panchromatic band). The polarization of the radarimage is HH and is of the PRI type and was digitally manipulated to remove speckleeffect and enhanced using several filters such as enhanced Lee and enhanced Frost.Several combinations of different optical data bands were tested to identify geologicalunits. The best separation between metamorphic rocks (CXG) and granites is providedby the RGB321 and HSI transform of RGB751 compositions, and between the two se-ries of granites by RGB754, RGB543 and RGB123 of principal component analysis;however, the quality of the separation is limited and not sufficiently effective to beused at the working scale of 1:50.000. An attempt of supervised classification basedon the available geological information was carried out using the HSI transform ofRGB751, but final results are still limited for a detailed separation of the geologicalunits. Radar data provided less useful results, showing no capabilities to distinguishbetween different geological units. Intense weathering of the rocks in this region, aswell as vegetation, are likely explanations for the poor response of spectral data (opti-cal and radar).Better results were obtained in the identification of structural lineaments with bothtypes of spectral data. Optical information of Landsat 7 ETM+ panchromatic band,with the application of directional filters, allow for a detailed identification of the frac-tures affecting the region (more than 4.000), and shows that dominant directions arecomprised between N30ºE to N60ºE, followed by N50W. Radar data is quite effectivein the identification of the most important tectonic structures, with less detail than op-tical information, and enhancing the recognition of some older structures not so welldefined in the manipulated panchromatic band.

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Remote sensing applied to geological mapping and tectonics : a study in the Viseu region, Central Portugal

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