M Shademan; A.R Arab-Amiri; H Kheyrollahi; D Rajabi
Abstract
Frequency Domain Electromagnetic surveys are being used for various applications like mineral and water exploration, environmental hazards and buried human-made materials because of its resolution and fast acquisition for low depth targets. Resistivity and its depth for each frequency could be calculated ...
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Frequency Domain Electromagnetic surveys are being used for various applications like mineral and water exploration, environmental hazards and buried human-made materials because of its resolution and fast acquisition for low depth targets. Resistivity and its depth for each frequency could be calculated in a simpler approach and shorter time than Iterative Inversion Method, Called Straight or Fast Inversion Methods, by assuming earth as a homogeneous half space. Barika’s Anomaly situated in Alut Geology 1:100,000 sheets in west Azerbaijan is studied in order to prospect gold_ lead mineralization which has been detected in systematic geochemical and litho-geochemical surveys. In this paper we studied different Fast Inversion algorithms for synthetic data then applied the best method for real data. Resistivity distribution for each frequency produced and appropriate interpretation according to geology acquired. The results showed that there is a good correlation between low resistivity and shear zones. Also geology map can be modified with higher frequency resistivity.
A.R. Arab-Amiri; A. Moradzadeh; D. Rajabi; B. Siemon; N. Fathianpour
Abstract
It is about 30 years that Helicopter electromagnetic (HEM) surveys are being used for rapid mineral and ground water exploration, environmental investigations and also geological mapping in extensive areas. Despite this, one of the most important problems in using obtained data from the surveys is accurate ...
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It is about 30 years that Helicopter electromagnetic (HEM) surveys are being used for rapid mineral and ground water exploration, environmental investigations and also geological mapping in extensive areas. Despite this, one of the most important problems in using obtained data from the surveys is accurate interpretation of the data. Otherwise, there will be no beneficial results while spending high costs. Thus the interpretation of the data is as old as the surveys. Several experts have tried to improve the interpretation of HEM data and they have achieved great successes. Almost the results of all these surveys are presented as resistivity (or conductivity)-depth sections. To reach this target, the first step is to solve the electromagnetic induction integral equation. As solving this integral is not possible using analytical methods, several numerical methods such as Laplace transformation, Hankel transformation and Jacobi-Matrix methods have been suggested for the solution of the integral, and different approaches have been presented with each method by various authorities. One of the most important solution methods is fast Hankel transformation. In this paper, it is attempted to use this method for finally obtaining resistivity-depth sections. For solving the induction equation by this method, we need the kernel function of the integral and weighting coefficients that replace the Bessel function in the integral. For this, first we use the Guptasarma-Singh method. Then results of this method are corrected and evaluated. Then, these results will be analyzed and tested with two synthetic models in addition to presenting the results of inverse modeling. Finally, by adding new parameter named α0 to induction equation, we will clearly see an improvement in the results of inverse modeling. Meanwhile, the problem of singularity that occurs at high frequencies is almost removed.
A.R. Arab-Amiri; A. Moradzadeh; D. Rajabi; N. Fathianpour; B. Siemon
Abstract
Today Helicopter-borne electromagnetic (HEM) data survey play important role for high resolution and fast 3D mapping of resistivity structures within the vast area. The standard method of interpretation of these data is to inverse them frequently. As surveying system is not fixed during the survey, hence ...
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Today Helicopter-borne electromagnetic (HEM) data survey play important role for high resolution and fast 3D mapping of resistivity structures within the vast area. The standard method of interpretation of these data is to inverse them frequently. As surveying system is not fixed during the survey, hence noise is accompanying the measured data. To process the measured noisy data they are fed into the several filters to get better data to be used for modeling. During the filtering stage some of signals are also lost. Therefore, it is required to choose modeling techniques that has minimum error and provide accurate subsurface model. In this paper, first the response of the three synthetic layered earth models were calculated by using three different Hankel transform forward modeling methods. Then with adding different percents of random noise to the synthetic data, they were modeled inversely by different methods. The obtained results indicate that the so-called improved Guptasarma-Singh inverse modeling method could provide better responses for all three synthetic models.
