Navegando por Assunto "Magnetometria"
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Item Acesso aberto (Open Access) Análise comparativa de três métodos de inversão aplicados a dados gravimétricos e magnéticos em perfil(Universidade Federal do Pará, 1985-10-07) CUTRIM, Alteredo Oliveira; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491Nonlinear inversion of potential field data has been traditionally accomplished by the least squares method. As far as the anomalous field is corrupted by Gaussian random noise. Least squares inversion has a good performance. However, when the data are contaminated by non Gaussian noise, which is the case of most geological noise, the least squares method presents an extremely poor performance. As a result, alternative methods must be employed in this case in order to produce realistic and meaningful interpretations. This paper presents a comparison among the least squares method, the minimum absolute error and M-fitting applied to non linear inversion of potential field data. The analysis is performed using theoretical data generated by synthetic models simulating several geological settings. The results show that in the presence of geological noise represented either by small shallow bodies above the main body, or by large interfering bodies adjacent to the main body, M-fitting presents a much batter performance as compared with the least squares or the minimun absolute error methods. In the presence of Gaussian random noise, however M-fitting has a poor performance. Since a Gaussian noise is a white noise, a law pass filter applied to the observed data would remove part of the Gaussian noise with a minimum loss of the low wavenumber signal. On the other hand, most geological noise have important low wavenumber spectral components so that this noise cannot be eliminated without a significant loss of signal. Therefore, the M-fitting method may become an important interpretation tool when applied to complex areas (where anomalies are usually contaminated by geological noise) provided the data have been previously filtered by a suitable law pass filter. All three methods analysed in the paper are applied to a real magnetic anomaly due to a dike of diabasic rock intruded in sandstones and shales from the Piauí Formation, in Parnaíba Basin, Brazil. All three methods yielded similar interpretations which are consistent with the available a priori geological information. The fact that all methods produced similar results indicates a low level of geological and Gaussian random noise in the data.Item Acesso aberto (Open Access) Desenvolvimento de um magnetometro a precessão nuclear(Universidade Federal do Pará, 1983-12-22) ALVES, José Geraldo das Virgens; BISCHOFF, Jürgen H.The objetive of this thesis was to develop a proton precession magnetometer for geophysical prospecting and base stations. The proton precession magnetometer measures the total magnetic field intensity. It operates on the basis of nuclear magnetic resonance by determining the precession frequency of protons of a non vicous liquid in the terrestrial .magnetic field. The magnetometer consists of two parts: the sensor and the measuring instrument. The sensor is a solenoildal coil with the liquid as the core. Three different liquids were tested: water, n-propanol and a laboratory grade kerosene. The last one was selected because it offers more high precession signal amplitude and, consequently higer signal/noise ratio. The measuring system contains the tunning and amplifier circuits and the logical circuits for programming the measuring cycle and count on the precession frequency. Each cycle has a duration of 3 seconds; 2.3 seconds for the polarization and 0.7 seconds for the reception of the signal. The operation can be carried out manually, automatically or by remote control. The precession signal is amplified selectively in one of 14 different syntonized band-passes for measurements between 22000 and 95000 gammas. The precession frequency is multiplied by 64 and counted for a time of 0.36699 seconds, selected in consideration to the gyromagnetic ratio of the proton. The number of counted pulses is numerically equal to the value of the magnetic field in gammas. The reading is displaed digitally. For remote operation a BCD output is availabe. The precision of the measurements is 1 gamma. The instrument was tested in field to evaluate signal/noise ratio, supportable gradient and battery consuption. Application teste was carried out to take diurnal variation data and, reconnaissance and detail surveys data on an archaeological site in the Marajó Island-Pa. The test results were confronted with two commercial magnetometers-GP-70, McPhar e G-816, Geometrics - and, with data from Observatório Magnetico Ilha de Tatuoca as well. For all cases, the data comparison showed a good performance of the magnetometer tested.Item Acesso aberto (Open Access) Gradiometria magnética e GPR aplicados à arqueologia em sítio estuarino em Penalva - MA(Universidade Federal do Pará, 2012-11-20) ROCHA, Herson Oliveira da; SILVA, Marcos Welby Correa; http://lattes.cnpq.br/3213216758254128This research presents the results of the application of geophysical methods noninvasive, in order to indicate possible sites of deposition of materials in archaeological survey at a site located in the municipality of estuarine Penalva in the state of Maranhão. The methods used were Magnetometry and Ground Penetrating Radar (GPR). The magnetic measurements were used to indicate the locations for excavation. The GPR was used to confirm the anomalies generated by the magnetic method, providing fewer errors when the magnetic anomalies are not caused by archaeological features. Were 14 profiles performed GPR using an antenna 400 MHz and 1664 magnetic measurements using the magnetometer. During the archaeological survey conducted, based on the geophysical anomalies provided by the team led by archaeologists Deusdedit Carneiro Leite Filho and Luiz Fernando Tavares Marques made five excavations at the site, which allowed them to rescue several ceramic pieces. The results presented in this study allowed us to verify and evaluate the potential of geophysical prospecting method to assist in archaeological studies.Item Acesso aberto (Open Access) Implantação do campo de testes da UFPA para medidas geofísicas(Universidade Federal do Pará, 2013) ALVES, Jerry Williamis Lima; LUIZ, José Gouvêa; http://lattes.cnpq.br/8676530374310847We describe the results obtained during the implementation of the Federal University of Pará test site for geophysical measurements. The work was done in three stages. In the first stage, preliminary studies were accomplished to know the physical background of the area. In the second, artifacts were buried to simulate geophysical anomalies in the measurements. In the third one, new measures were performed to detect anomalies caused by the buried artifacts. Only a part of the artifacts that are scheduled for burial was buried in the site. The buried artifacts are metal pipes, metal drums, and plastic drums. The measures implemented in the first and third stages involved the methods of Electrical Resistivity, Ground Penetrating Radar (GPR), Electromagnetic and Magnetic. The measurements performed in the third stage showed the presence of artifacts in the actual position where they were buried, which turns the area suitable to serve as a training site for geophysical experimental practices.Item Acesso aberto (Open Access) Inversão conjunta de dados gravimétricos magnéticos e resistivo(Universidade Federal do Pará, 1986-05-15) SOUZA, Cleomar Fernandes de; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491Despite its advantages, the application of joint inversion to real data is not a current practice. One of the difficulties involving joint interpretation of geophysical data is the lack of systematic studies designed to assess its performance in a variety of simulated geological settings. This thesis is a contribution to this kind of study. This thesis compares the inversion of three sets of geophysical data: gravity, magnetic, and resistivity. The standard inversions of each set are compared with the 3 possible joint inversions of two sets of data, and also with the joint inversion involving the three sets. The comparison is performed using sinthetic data produced by a two-dimensional rectangular prism with finite thickness, and the least squares method is employed in the solution of the standard nonlinear problem of determining the prism parameters. The criteria adopted for the comparison were the parameter estimates themselves, the parameter standard deviations (for gravity and magnetic inversion of noise corrupted data), and also the reduction of ambiguity detected by the dependence of the parameter estimates on the initial guess. We found that, in general, the joint inversion using two sets of data produces better results than the inversion of each individual set. On the other hand, the results of the joint inversion employing all three sets are similar to the results of the joint inversions using two sets of data. In some cases, however, the joint inversion using all three sets is the only one virtually independent of the initial guess. Applications to real anomalies are presented.Item Acesso aberto (Open Access) Investigação com os métodos GPR e magnético de urnas funerárias do Sítio Nossa Senhora do Perpétuo Socorro (Pará)(Universidade Federal do Pará, 2012-09-21) SILVEIRA, Eric Sandro Ferreira da; SILVA, Lúcia Maria da Costa e; http://lattes.cnpq.br/8612431024609774This paper presents the results of the application of geophysical methods in the selection of potential areas for archeological site at Nossa Senhora do Perpétuo Socorro in the state of Pará. The site has urns indigenous outcropping and sub-outcropping plenty of archaeological interest. The methods used were Magnetometry and Ground Penetrating Radar (GPR). The magnetic measurements were employed to indicate the most appropriate sites for excavation greatly reducing the potential areas. The GPR was used to confirm the anomalies detected by magnetic measurements and provide a better spatial assessment both horizontally and vertically, reducing the errors when they identify magnetic anomalies that are not caused by archaeological features. The study methodology was based on comparison of anomalies obtained from unknown areas which anomalies from areas where exists urns and roots, characterizing and grouping these anomalies.Item Acesso aberto (Open Access) Metodologia geofísica aplicada à pesquisa de salvamento arqueológico nos sítios Bittencourt, Jambuaçu e Jaburu, Estado do Pará(Universidade Federal do Pará, 2006-05-02) ARAGÃO, Rigler da Costa; LUIZ, José Gouvêa; http://lattes.cnpq.br/8676530374310847We present the results obtained in the application of geophysical methods to help the archaeological rescue of remains in the three following sites in Pará, northern of Brazil: Bittencourt, located in Abaetetuba; Jambuaçu, located in Moju; and Jaburu, located in Almeirim. Magnetometry, scintillometry and ground penetrating radar (GPR) were used in the study. Magnetic measurements were taken as the main tool to indicate places for excavation. GPR was used to confirm the anomalies detected with the magnetic method and provided a restriction to the magnetic anomalies caused by non-archaeological artifacts. Scintillometry was used as an attempt to map the archaeological black earth (ABE) or Terra Preta Arqueológica (TPA) soil through the detection of natural gamma ray emitted by the ground. The excavations carried out on the indications of magnetometry and GPR yielded the recovery of ceramics, faience, lithics, and iron artifacts. The scintillometric data showed that exist a good correlation between low radiation and large thickness of ABE (TPA). The used geophysical methodology proved to be efficient and quick with no destructive impact to the sites.Item Acesso aberto (Open Access) Metodologia geofísica aplicada ao estudo arqueológico dos sítios Bittencourt e Jambuaçu, Estado do Pará(2010-06) ARAGÃO, Rigler da Costa; LUIZ, José Gouvêa; LOPES, Paulo Roberto do CantoMagnetic, total count gamma radiation, and Ground Penetrating Radar (GPR) measurements were carried out on two archaeological sites located adjacent to the place where a miner duct will be buried. The aim of the measurements was to indicate the optimal áreas for archaeological excavation to find subsurface remains related to ancient communities that lived in the sites. Magnetic measurements showed anomalies that lead to the discovery of a large amount of ceramic fragments and other remains. Gamma radiation allowed discriminating argillaceous from sandy soil, an important result since sandy soil can be correlated to the archaeological layer, where remains are normally found. Ground penetrating radar confirmed the magnetic anomalies and showed several other anomalous features not related to the archaeological remains.Item Acesso aberto (Open Access) Métodos geofísicos aplicados à prospecção de cobre na Serras de Carajás - Pará(Universidade Federal do Pará, 1980-03-20) HOOKER, Enrique Campbell; SAUCK, William August; http://lattes.cnpq.br/6655455534234531Through an agreement between the Federal University of Para and the Rio Doce Geologia e Mineração Company, a geophysical research was carried out in the area known as ALVO 1, MM1, Serra dos Carajás, south of Para, Brazil. The magnetic, electrical induced polarization and AFMAG methods were applied, to detect the distribution of copper in subsurface. This work was carried out both on a 9 km2 reconnaissance area (ALVO 1) and on a 0.63 km2 detail area (Corpo 2). The AFMAG method detected various conductors displaced from each other by possible faulting. The orientation of these conductors, coincides with the dominant strike of the body of schist which contains copper sulfide, associated with an iron formation. The close correlation they have with the magnetic anomaly, may imply that the AFMAG anomalies are caused, firstly by the iron formation and secondarily by the sulfide. The magnetic method detected strong anomaly over the iron formation. The displacement of the segment of the anomaly impleis faulting. This method is very important in the area due to the association of the sulfide zone with the iron formation. The electrical induced polarization/resistivity method detected anomalies with PFE, varying from 6 to 12% approximately. Several of these anomalies were confirmed by mechanical sounding and laboratory research (Rocha, 1979). It was verified that these anomalies were caused by a combined effect of the iron formation and the sulfide body. The geophysical research carried out at this pilot area turned out to be very important considering the fact that its results can be successfully extrapolated to a larger area with the same geological characteristics.Item Acesso aberto (Open Access) Métodos geofísicos aplicados a prospecção mineral na região do Igarapé Chega Tudo, Maranhão - Brasil(Universidade Federal do Pará, 1982-12-29) ORTEGA GONZALEZ, Moisés; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676This work of geophysical prospecting was carried out on a NW-SE geological lineament zone from Chatão - on the right side of Gurupi river up to 5 km beyond Chega Tudo in the State of Maranhão. The field work with the application of magnetic (total field), radiometric, electroresistivity (Schlumberger, Wenner and Half-Schlumbergere) and EM (Sligram) methods was carried out in two stages: a) reconnaissance survey of a 22 km2 area with magnetic and radiometric methods, and b) detailed survey of a 3.5 km2 area with electroresistivity and EM methods. The objectives were to study the main geoelectrical structures associated with mineralized zones, and to select among the used geophysical techniques the one with greater resolution to locate sub-surface quartz veins with gold mineralization. The magnetic method shows a large anomaly in the NE region of the area of reconnaissance, whereas the radiometric method indicates only the background value everywhere. Therefore the latter will be not discussed. The electroresistivity and EM surveys indicate many important anomalies on the detailed area. The electroresistivity and magnetic interpretation were carried out by computacional techniques whereas the EM data were interpreted by phase diagrams. The results show a good correlation between the magnetic and electroresistivity anomalies and the mineralized zone. The EM method was not found effective because it could not discriminate the anomalies inside and outside the mineralized zone. All anomalies were tested with well logs. Since the studied area has the same degree of difficulties for geological prospecting as any other similar area in the Amazon region, the results presented here show that the magnetic and electroresistivity methods, which turned out to be very effective as exploration tools for prospecting gold at Chega Tudo region, could be applied to any other environment with similar geological characteristics.Item Acesso aberto (Open Access) Métodos geofísicos aplicados ao mapeamento geológico numa área da Região Bragantina-Pará(Universidade Federal do Pará, 1979-12-13) FERREIRA, João Batista; SAUCK, William August; http://lattes.cnpq.br/6655455534234531The following research is about the aplication of geophysical methods in a pilot area in the Bragantina region, NE of Pará, as an auxiliary to geologic mapping. The area is covered with thick tertiary sediments and presents occurrences of industrial rocks such as limestone and granite, representing an outcrop surface smaller than 5% of area. Studies carried out by Goulart (1978) revealed that it is impossible to determine parent rock of the superficial material, of the A horizon. This makes difficult the surface geologic mapping and can lead to exaggerated extrapolation of the contacts, such as that which took place in the preliminary mapping. The geophysical methods applied in the area are: Electroresistivity and Magnetometry. Some mechanical sounding was carried out also. The results obtained contributed to a better understanding of the structural features mapped, and also made it possible to discover other important features. Two areas were defined for future detail study, with the objective to distinguish between the limestones of better and poorer quality. In reference to the granite region a new mapping of that area is suggested.Item Acesso aberto (Open Access) Métodos geofísicos aplicados ao ultramafito da Serra de Quatipuru - Estado do Pará(Universidade Federal do Pará, 1980-05-13) BELTRÃO, Jacira Felipe; LOURENÇO, José SeixasThe objective of the present work is the application of geophysical methods for the economical evaluation of Ni, Cr and asbestos occurrences in an area of 6.25 km2 - Malha 2 - in Sierra Quatipuru 50 km SW of Conceição do Araguaia, in the South of the State of Pará. Magnetic methods were applied initially for reconnaissance, using total and vertical field magnetometers, in order to locate anomalous zones of asbestos and cromite, associated with magnetite. The electromagnetic method of dip-angle was used to define conductive zonas associated with possible mineral deposits or structural features. Based on the interpretation of the magnetic and electromagnetic data several areas defined for the application of the induced polarization-resistivity method aiming at possible deposits of dissemineted sulphides as the main targets. The possible occurrences of mineral deposits in the area were correlated with the geophysical anomalies and were investigated further by drilling. It was concluded that occurrences do not have economic interest. However, the application of these geophysical methods was successful in the investigation of this problem as they have advantages over the more conventional methods which are expensive and time consuming.Item Acesso aberto (Open Access) Separação regional-residual em magnetometria através de camadas equivalentes(Universidade Federal do Pará, 1987-12-28) COSTA, Jessé Carvalho; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491