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Magnetic Sources (magnetic + source)

Distribution by Scientific Domains

Earth and Environmental Science	57%

Selected Abstracts

Imaging magnetic sources using Euler's equation

GEOPHYSICAL PROSPECTING, Issue 1 2002
Shu-Kun Hsu
ABSTRACT The conventional Euler deconvolution method has the advantage of being independent of magnetization parameters in locating magnetic sources and estimating their corresponding depths. However, this method has the disadvantage that a suitable structural index must be chosen, which may cause spatial diffusion of the Euler solutions and bias in the estimation of depths to the magnetic sources. This problem becomes more serious when interfering anomalies exist. The interpretation of the Euler depth solutions is effectively related to the model adopted, and different models may have different structural indices. Therefore, I suggest a combined inversion for the structural index and the source location from the Euler deconvolution, by using only the derivatives of the magnetic anomalies. This approach considerably reduces the diffusion problem of the location and depth solutions. Consequently, by averaging the clustered solutions satisfying a given criterion for the solutions, we can image the depths and attributes (or types) of the causative magnetic sources. Magnetic anomalies acquired offshore northern Taiwan are used to test the applicability of the proposed method. [source]

An appraisal of the Serra da Cangalha impact structure using the Euler deconvolution method

METEORITICS & PLANETARY SCIENCE, Issue 8 2005
A. Adekunle ADEPELUMI
The efficacy of the method has been evaluated using the aeromagnetic data obtained over the Serra da Cangalha impact crater, northeastern Brazil. The analyses of the data have provided characteristic Euler deconvolution signatures and structural indices associated with impact craters. Also, through the interpretation of the computed Euler solutions, our understanding of the structural features present around the impact structure has been enhanced. The Euler solutions obtained indicate shallow magnetic sources that are interpreted as possibly post-impact faults and a circular structure. The depth of these magnetic sources varies between 0.8 and 2.5 km, while the Precambrian basement depth was found at ,1.5 km. This is in good agreement with the estimates of the Precambrian basement depth of about 1.1 km, calculated using aeromagnetic data. The reliability of the depth solutions obtained through the implementation of the Euler method was confirmed through the use of the existing information available in the area and the result of previous studies. We find that the Euler depth solutions obtained in this study are consistent with the results obtained using other methods. [source]

Analysis of magnetic source localization of P300 using the multiple signal classification algorithm

PSYCHIATRY AND CLINICAL NEUROSCIENCES, Issue 6 2006
TETSUO UOHASHI md
Abstract, The authors studied the localization of P300 magnetic sources using the multiple signal classification (MUSIC) algorithm. Six healthy subjects (aged 24,34 years old) were investigated with 148-channel whole-head type magnetencephalography using an auditory oddball paradigm in passive mode. The authors also compared six stimulus combinations in order to find the optimal stimulus parameters for P300 magnetic field (P300m) in passive mode. Bilateral MUSIC peaks were located on the mesial temporal, superior temporal and parietal lobes. Interestingly, all MUSIC peaks in these regions emerged earlier in the right hemisphere than in the left hemisphere, suggesting that the right hemisphere has predominance over the left in the processing activity associated with P300m. There were no significant differences among the six stimulus combinations in evoking those P300m sources. The results of the present study suggest that the MUSIC algorithm could be a useful tool for analysis of the time-course of P300m. [source]

Decorrugation, edge detection, and modelling of total field magnetic observations from a historic town site, Yellowstone National Park, USA

ARCHAEOLOGICAL PROSPECTION, Issue 1 2010
Steven D. Sheriff
Abstract Cinnabar, Montana is a historic town site and railroad depot near the northern edge of Yellowstone National Park and was inhabited between 1883 and 1903. Remains of foundations and old photographs help determine the area of the town, but the south and east limits are unknown. We acquired total field magnetic intensity data to help determine the full extent of the town. Randomly distributed ferrous magnetic sources on the surface and typical noise associated with acquisition complicate the signal. To separate signal and noise we applied filtering and edge detection techniques common in the aeromagnetic industry to our data. Regional removal, decorrugation, upward continuation, and edge detection successfully separated signal and noise. Following filtering, we extracted two larger anomalies from the data set. For those two anomalies, we estimated the edges of their causative sources by calculating the maxima in the horizontal gradient of their anomalies and by inverse modelling those sources; both methods yield similar results. An archaeological test unit excavation within one of the anomalies clearly indicates the remains of buried domestic features, the foundation to a house or other building associated with the late nineteenth to early twentieth century use of Cinnabar. Thus the southeast extent of Cinnabar is greater than previously thought. The lack of surface indicators or adequate historic photography precluded the identification of this buried feature without the aid of the magnetic study. Copyright © 2009 John Wiley & Sons, Ltd. [source]