1,721,165 research outputs found
Time variation and high definition study of the geomagnetic field space structure in the eastern Ligurian sea (Italy),
No full textDepth-to-the-bottom optimization for magnetic data inversion: Magnetic structure of the Latium volcanic region, Italy
No full textWe present an algorithm for the linear inversion of two-dimensional (2-D) surface magnetic data to obtain 3-D models of the susceptibility of the source. The forward model is discretized by a mesh of prismatic cells with constant magnetization that allows the recovery of a complete 3-D generating source. As the number of cells are normally greater than the amount of available data, we have to solve an underdetermined linear inverse problem. A Tikhonov regularization of the solution is introduced as a depth-weighting function adapted from Li and Oldenburg (1996) to close the source toward the bottom. The main novelty of this method is a first-stage optimization that gives information about the depth to the bottom of the generating source. This parameter permits both the evaluation of the appropriate vertical extension of the mesh and the definition of the shape of the regularizing depth-weighting distribution. After discussing the performance of this method by showing the results of various synthetic tests, we invert the magnetic anomalies of the volcanic edifices in the Latium region in central Italy to define their 3-D source distribution. Copyright 2006 by the American Geophysical Union
Marine geomagnetic high definition metrology; possible archaeological applications
No full textThe marine geomagnetism is often used to solve geological problems at a regional scale: structural, volcanological or mining problems, for instance (Faggioni et al., 1995). In recent time, the development of the “high definition (HD) metrology” (Faggioni et al., 2001) has made the marine geomagnetic method suitable for detecting short wavelength and low amplitude geomagnetic anomalies. This type of signal may be often related to environmental and/or archaeological sources.......UnpublishedCracow – Poland1.8. Osservazioni di geofisica ambientaleope
Marine geomagnetic high definition metrology; possible archaeological applications
No full textThe marine geomagnetism is often used to solve geological problems at a regional scale: structural, volcanological or mining problems, for instance (Faggioni et al., 1995). In recent time, the development of the “high definition (HD) metrology” (Faggioni et al., 2001) has made the marine geomagnetic method suitable for detecting short wavelength and low amplitude geomagnetic anomalies. This type of signal may be often related to environmental and/or archaeological sources.......UnpublishedCracow – Poland1.8. Osservazioni di geofisica ambientaleope
Gaussian envelope for 3D geomagnetic data inversion
No full textWe describe an inversion method for 3D geomagnetic data based on approximation of the source distribution by means of positive constrained Gaussian functions. In this way, smoothness and positivity are automatically imposed on the source without any subjective input from the user apart from selecting the number of functions to use. The algorithm has been tested with synthetic data in order to resolve sources at very different depths, using data from one measurement plane only. The forward modeling is based on prismatic cell parameterization, but the algebraic nonuniqueness is reduced because a relationship among the cells, expressed by the Gaussian envelope, is assumed to describe the spatial variation of the source distribution. We assume that there is no remanent magnetization and that the magnetic data are produced by induced magnetization only, neglecting any demagnetization effects. The algorithm proceeds by minimization of a X 2 misfit function between real and predicted data using a nonlinear Levenberg-Marquardt iteration scheme, easily implemented on a desktop PC, without any additional regularization. We demonstrate the robustness and utility of the method using synthetic data corrupted by pseudorandom generated noise and a real field data set
A metrologic method of anomaly field amplitude bottom reduction in undersampled geomagnetic marine surveys
No full textWe show the results obtained by means of a seabed reduction technique on the intensity of geomagnetic anomaly fields applied to a synthetic case and then to the real case of a geomagnetic survey of eastern Ligurian Sea (Italy). The eastern Ligurian Sea has very intense short waves anomaly fields and a sea bed that varies greatly in depth. As a result the geomagnetic space signal is characterized by a very large spectral content; in these conditions it is not possible to obtain a full sampled marine survey and vertical continuation analytic procedures and standard numerical bottom reduction based on a single vertical incremental parameter, whichever is applicable, fails to give accurate results. The present technique, which has been fine-tuned over 4 years of experimentation in environmental researchs, aims to provide a simple and efficient means to reduce the distortion of geomagnetic anomalies field caused by the variation of distance between survey plane and magnetic outcrop source position. The compensation procedure is based on evaluation, by comparison of two measurements carried out at different altitudes, of the mean vertical increment typical of each anomaly field principal frequency component bands. The component anomaly fields are then corrected by application of the corresponding vertical increments and lastly, the anomaly geomagnetic field reduced to the sea-bed is computed as Inverse Fourier Transform of a spectrum built as synthesis of the component anomaly fields' spectra. The results obtained have shown a notable increase in definition of anomaly field intensity without the production of appreciable distortions or false geomagnetic echoes
Shaded relief magnetic anomaly map of Italy and surrounding marine areas
No full textMagnetic observations made onshore the Italian Peninsula, and across the adjacent seas. have been compiled in a new digital database that provides the first complete regional scale view of the crustal scale magnetic anomalies of the region at sea level. The offshore data were acquired between 1965-1972 by the Osservatorio Geofisico Sperimentale (OGS) while the ground measurements were performed within the framework of the Progetto Finalizzato Geodinamica of the Consiglio Nazionale delle Ricerche (PFG-CNR) between 1977 and 1981. The new shaded relief magnetic anomaly map of total intensity of the Earth's magnetic field for Italy and the surrounding seas has been produced at sea level, for the geomagnetic epoch 1979.0. The most remarkable result of this new map, with respect to the previous compilations and to the aeromagnetic map of Italy, is an unprecedented view of the magnetic signature of the major tectonic elements in their regional setting. There is good correlation between known structural geology and the magnetic anomalies, and now that the longer wavelength signatures: have been corrected, deeper interpretations are possible
Geomagnetic Time Variations and High Definition Study of Space Magnetic Effects Induced by Artificial Submerged Sources
No full textWe describe a technique for high definition marine coastal survey in which we have used to locate possible artificial magnetic sources, such as wrecks, in the Eastern Ligurian Sea. The data were recorded with a marine proton magnetometer using a high density grid ….Marina Militare Italiana, Witehead Alenia Sistemi SubacqueiPublished221 - 2281.8. Osservazioni di geofisica ambientaleN/A or not JCRope
Geomagnetic Time Variations and High Definition Study of Space Magnetic Effects Induced by Artificial Submerged Sources
No full textWe describe a technique for high definition marine coastal survey in which we have used to locate possible artificial magnetic sources, such as wrecks, in the Eastern Ligurian Sea. The data were recorded with a marine proton magnetometer using a high density grid ….Marina Militare Italiana, Witehead Alenia Sistemi SubacqueiPublished221 - 2281.8. Osservazioni di geofisica ambientaleN/A or not JCRope
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