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A backscattering lidar system, the first of this kind in Brazil, has been used to provide the vertical profile of the aerosol backscatter coefficient at 532 nm up to an altitude of 4-6 km above sea level (ASL), in a suburban area in the city of São Paulo. The lidar system has been operational since September 2001. The lidar data products were obtained in a 4-yr period (2001-04) and concerned the aerosol optical thickness (AOT), the aerosol backscattering and extinction coefficients at 532 nm, cloud properties (cloud base, thickness), planetary boundary layer (PBL) heights, aerosol layering, and the structure and dynamics of the lower troposphere. The lidar data are presented and analyzed in synergy with AOT measurements obtained by a Cimel sun-tracking photometer in the visible spectral region, not only to validate the lidar data but also to provide an input value of the so-called extinction-to-backscatter ratio [lidar ratio (LR)]. A correlation between the lidar data and the data obtained by a Cimel sun-tracking photometer [belonging to the Aerosol Robotic Network (AERONET)] is being made to set a temporal database of those data that were collected concomitantly and to cross correlate the information gathered by each instrument. The sun photometer data are used to provide AOT values at selected wavelengths and thus to derive the Ångström exponent (AE) values, single scattering albedo (SSA) and phase function values, and LR values. The analysis of these data showed an important trend in the seasonal signature of the LR indicating a change of the predominant type of aerosol between the dry and wet seasons. Thus, during the wet season the LR lidar values are greater (50-60 sr), which indicates that larger absorption by the aerosols takes place during this period. The corresponding AE values range between 1.3 and 2 for both periods.

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E comum o uso da modelagem gravimétrica de greenstone belts devido ao alto contraste de densidade entre as rochas que preenchem o greenstone (geralmente metamáficas e metaultramáficas) e o seu embasamento (geralmente gnaisses e granitos). O presente trabalho faz uma estimativa da geometria do greenstone belt na região da cidade de Pitangui em Minas Gerais-Brasil. Para tal foram realizadas 5 sessões de modelos gravimétricos 2D usando como vínculos uma seção sísmica publicada, seções retiradas da inversão do vetor magnetização (MVI), que foi calculada sobre os dados magnetométricos e os limites geológicos mapeados. As modelagens apresentaram a estimativa da geometria do greenstone belt em profundidade, independente se ele aflora ou não. A profundidade máxima do greenstone belt variou de 1 a 5 km, aproximadamente, sendo que a calha vai ficando mais rasa na porção Sul do greenstone belt. Os limites do corpo anômalo modelado mostraram um contato abrupto do greenstone belt com o embasamento. Os limites laterais (afloramentos ou não) foram estimados por meio do mapa gravimétrico de anomalia Bouguer. Um resultado importante da modelagem foi o prolongamento do greenstone beltà NW, sob o Grupo Bambuí. Palavras-chave: modelagem gravimétrica; inversão do vetor magnetização; greenstone belt Pitangui.

According to the Poisson theorem, gravity and magnetic fields arising from geological bodies that share common sources, with uniform magnetization-to-density ratio and uniform magnetization direction, are related by a linear transformation that allows each field to be calculated from the other. Provided these conditions on the sources are met, when both gravity and magnetic data are available over an area the Poisson theorem can be used to infer magnetization-to-density ratios and magnetization directions of sources from their associated gravity and magnetic anomalies. These conditions are partially met in many geological structures but are expected in iron ore deposits, usually associated with strongly magnetic and highly density formations. Due to the importance of iron ore as a global commodity, most mineral provinces of the world have been investigated by accurate gravity and magnetic sensors, providing a reliable database but not yet explored with joint interpretation based on Poisson’s relationships. We interpret a gravity-magnetic survey covering the Serra Sul of the Caraj’s Mineral Province, Brazil, where world class iron deposits are found. We adapted a formulation formerly developed to estimate the magnetization-to-density-ratio (MDR) and the magnetization inclination (MI) from profile data to process gridded data sets. Due to faulting and folding, the same dense and magnetic structure may assume different strike directions, requiring corrections to improve MDR and MI estimates. Because the geomagnetic field inclination in the studied area is very low (−6.7°), a procedure for stable computation of the components of the anomalous magnetic field vector is applied. The inferences for Serra Sul MDR suggest minor variations for the entire 30 km long formation containing the mineralized bodies, the strong remanent magnetization showing reverse polarity for BIF segments of the Caraj’s Serra Sul.