Subcontinental Geologic Mapping using the MMRS Sensor (SAC-C Satellite Mission-Matutine Constellation). - An example of central regions of South America Methods The SAC - C raw digital imagery CD disks data were supplied by the CONAE (Comisión Nacional de Actividades Espaciales de la Argentina, after an A/O agreement with the Department of Applied Geosciences, Engineery Faculty, National University of Northeastern (UNNE), Argentina) and then we used them for this work. The SAC - C paths (orbits) employed here are: 223/000, 224/000, 225/000, 226/000, 227/000, 228/000 and 229/000. The lighthing hour of ilumination was 10:45 a.m. Argentina time which correspond to 14:45 p.m. West Greenwich Meridian. The date of acquisition of all digital data were summer and automn 2002, Austral Hemisphere. We analyze the matrix structure of the digital data images. Then, we cut aproximately a half image per path. This is because a lot of cloud presence overlies the Amazonas region (Brazil) and the extreme south of Argentina. The extension of the scenes employed herein, which cover all South America, also were taken in consideration because the size of the files were extremely large in size to handle into ATX PCs standards (more than 1,2 Gb per file). After this, we create false color images for all the scenes and then mosaicking. Composition 4/5/3 and 3/4/5 were maked for geological, tectonical, morphological and vegetate coberture analyses. It is convenient to be present that the pixel dimension of these images is about 125 meters and so, it is not represent great precision in assembage. But on the contrary, they give us a very aproximate idea of the contextual regional main patterns. On the other hand, we have present the focus of our work which was cualitative and not quantitative. The automatized classification were done used standard procedures as standard IDRISI® modules. We performed unsupervided and supervised tests. Because the amplitude involucred in this work, we categorize seven wide classes of cobertures as follow: vigorous vegetation (forest, woods, etc.), scrub and mixed grassland terrains (including intertropical sabannas with aloctonous palms), water masses (wetlands, lagoons, lakes, large rivers and it fluvial wide plains, etc.), several soils without organic coberture and few level of moisture (sometimes deforestation terrains and incipient desertification), soils with active agriculture but without discrimination among species and period of grouth, outcrops of recent Quaternary basat-alkaline volcanic aparatous, antropic constructions (urban, peri-urban and large cities). Better results were obtained with supervided clasification although when the operators are well familiarized with previous results and so be able to configure adequately algoritms into the computational modules, the automatic classifications offers very similar results those of supervised classifications. First orders geological, tectonical and morphological elements were outlined by means of in-screen digitalization using standard applications (software) as AutoCAD®. Results Main large crustal lineaments, not previously mentioned and never properly understood, were carefully detected and draw. The keys used for mapping lineaments were shadows and highlights and abrupt change of cobertures which implies a drastic variation into the tone-area and so lithology. The analyses of the main physiographical features as river drainage, low ranges, extense plains, large lagoons models, immense wetland masses models, deltas models, curvilines scarpments models, several extense faulting lineaments models were employed for interpretation. The present of some volcanic aparatous dome-model of Quaternary age were used too as an important tool for interpretation. The recognition of volcanic dome have two very different aspects: at the selvatic region they are covered by vigorous vegetation and so they give strong reddish colors apart from its typical geoform. At the areas with scarce vegetation they are circular and extremely fractured (see Figure 2). The wetland areas are characterized by dark tones whereas the agriculture areas present typical geometrical patterns as well as urban, peri-urban and large cities. The soils with low moisture and scarce vegetation are always brilliant. Incipient erosion processes are very well recognized in the head water drainage gullies, destroying silt materials (see Figure 3). The vigorous woods are brown dark tones and strong in texture, which sometimes is lobulated and so characteristic (Morello, 1968, Morelo and Adamoli, 1974). 
The geological and tectonical first orders lineaments are clearly recognizable because its continuous mark into the composition scenes. Many times they separe different tonal color and texture designs, specially towards the east of the study area (e.g. Paraguay and Brazil). |