Fatoração QR como ferramenta para a determinação de poços principais em redes de monitoramento de aqüíferos freáticos

Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, 2008.Redes de monitoramento da variabilidade piezométrica são cada vez mais utilizadas para a avaliação e gestão de aqüíferos. Com o objetivo de determinar poços principais, foi utilizada uma versão da decomposição QR com pivoteamento em quatro redes. Uma das redes está localizada na bacia do alto rio Jardim, na porção leste do Distrito Federal, e as outras três no sul do estado do Tocantins, como parte do monitoramento hidrogeológico para a construção da barragem da AHE Peixe Angical. Uma vez definidos os poços principais, a superfície piezométrica nos demais poços é calculada através de uma abordagem por quadrados mínimos, que define regiões de controle da variabilidade piezométrica. Estas regiões coincidem com a cobertura pedológica da região. Para a rede da bacia do alto rio Jardim, foi possível reduzir em 82% o número de poços a serem monitorados, e nas redes do sul do Tocantins, houve uma redução de aproximadamente 50%. A simulação do movimento dos níveis da água feitos a partir dos registros dos poços principais selecionados retornou 99% de correlação com a variação original. _________________________________________________________________________________ ABSTRACTMonitoring networks of piezometric motion are increasingly used for evaluation and management of aquifers. A pivoted version of the QR factorization was used in four networks, with the purpose of determining principal wells. One network is located at river Jardim watershed, at the east portion of Distrito Federal, Brazil, and the other three are located in south portion of Tocantins state, as part of the hydrogeologic monitoring for the construction of AHE Peixe Angical dam. Once defined the principal wells, the piezometric surface is calculated through a least-squares approach, which determines control regions of piezometric variability. Those regions match with soil coverage. At the river Jardim watershed, it was possible to reduce in 82% the number of wells to be monitored. The networks located in south Tocantins were reduced in 50% approximately. The water level movement simulation generated from principal wells records returned 99% correlation with original fluctuation

A statistics-based descriptor for automatic classification of scatterers in seismic sections

Discontinuities and small structures induce diffractions on seismic or ground-penetrating radar (GPR) acquisitions. Therefore, diffraction images can be used as a tool to access valuable information concerning subsurface scattering features, such as pinch outs, fractures, and edges. Usually, diffraction-imaging methods operate on diffraction events previously detected. Pattern-recognition methods are efficient to detect, image, and characterize diffractions. The use of this kind of approach, though, requires a numerical description of image points on a seismic section or radargram. We have investigated a new descriptor for seismic/GPR data that distinguishes diffractions from reflections. The descriptor consists of a set of statistical measures from diffraction operators sensitive to kinematic and dynamic aspects of an event. We develop experiments in which the proposed descriptor was incorporated into a pattern-recognition routine for diffraction imaging. The obtained method is useful for performing the automatic classification of image points using supervised and unsupervised algorithms, as a complementary step to Kirchhoff imaging. We also develop a new type of filtering, designed to address anomalies on the diffraction operators caused by interfering events. We evaluate the method using synthetic seismic data and real GPR data. Our results indicate that the descriptor correctly discriminates diffractions and shows promising results for low signal-to-noise-ratio situations