共查询到20条相似文献，搜索用时 26 毫秒
1.
E. M. Abdelrahman K. S. Soliman E. R. Abo-Ezz K. S. Essa T. M. El-Araby 《Pure and Applied Geophysics》2009,166(12):2021-2035
We have developed a new numerical method to determine the shape (shape factor), depth, polarization angle, and electric dipole moment of a buried structure from residual self-potential (SP) anomalies. The method is based on defining the anomaly value at the origin and four characteristic points and their corresponding distances on the anomaly profile. The problem of shape determination from residual SP anomaly has been transformed into the problem of finding a solution to a nonlinear equation of the form q = f (q). Knowing the shape, the depth, polarization angle and the electric dipole moment are determined individually using three linear equations. Formulas have been derived for spheres and cylinders. By using all possible combinations of the four characteristic points and their corresponding distances, a procedure is developed for automated determination of the best-fit-model parameters of the buried structure from SP anomalies. The method was applied to synthetic data with 5% random errors and tested on a field example from Colorado. In both cases, the model parameters obtained by the present method, particularly the shape and depth of the buried structures are found in good agreement with the actual ones. The present method has the capability of avoiding highly noisy data points and enforcing the incorporation of points of the least random errors to enhance the interpretation results. 相似文献
2.
Khalid S. Essa 《Acta Geophysica》2007,55(2):182-190
This paper presents a simple method for shape and depth determination of a buried structure from residual gravity anomalies
along profile. The method utilizes the anomaly values of the origin and characteristic points of the profile to construct
a relationship between the shape factor and depth of the causative source. For fixed points, the depth is determined for each
shape factor. The computed depths are then plotted against the shape factor representing a continuous monotonically increasing
curve. The solution for the shape and depth of the buried structure is then read at the common intersection point of the depth
curves. This method is applied to synthetic data with and without random errors. Finally, the validity of the method is tested
on two field examples from the USA. 相似文献
3.
E. M. Abdelrahman H. M. El-Arby T. M. El-Arby K. S. Essa 《Pure and Applied Geophysics》2003,160(7):1259-1271
—We have developed a least-squares minimization approach to depth determination from magnetic data. By defining the anomaly value T(0) at the origin and the anomaly value T(N) at any other distance (N) on the profile, the problem of depth determination from magnetic data has been transformed into finding a solution to a nonlinear equation of the form f(z)=0. Formulas have been derived for a sphere, horizontal cylinder, dike, and for a geologic contact. Procedures are also formulated to estimate the effective magnetization intensity and the effective magnetization inclination. A scheme for analyzing the magnetic data has been formulated for determining the model parameters of the causative sources. The method is applied to synthetic data with and without random errors. Finally, the method is applied to two field examples from Canada and Arizona. In all cases examined, the estimated depths are found to be in goodagreement with actual values. 相似文献
4.
El-Sayed M. Abdelrahman Eid. R. Abo-Ezz Khalid S. Essa T.M. El-Araby Khaled S. Soliman 《Geophysical Prospecting》2007,55(3):433-446
We have developed a least‐squares minimization approach to depth determination using numerical second horizontal derivative anomalies obtained from magnetic data with filters of successive window lengths (graticule spacings). The problem of depth determination from second‐derivative magnetic anomalies has been transformed into finding a solution to a non‐linear equation of the form, f(z) = 0. Formulae have been derived for a sphere, a horizontal cylinder, a dike and a geological contact. Procedures are also formulated to estimate the magnetic angle and the amplitude coefficient. We have also developed a simple method to define simultaneously the shape (shape factor) and the depth of a buried structure from magnetic data. The method is based on computing the variance of depths determined from all second‐derivative anomaly profiles using the above method. The variance is considered a criterion for determining the correct shape and depth of the buried structure. When the correct shape factor is used, the variance of depths is less than the variances computed using incorrect shape factors. The method is applied to synthetic data with and without random errors, complicated regionals, and interference from neighbouring magnetic rocks. Finally, the method is tested on a field example from India. In all the cases examined, the depth and the shape parameters are found to be in good agreement with the actual parameters. 相似文献
5.
E. M. Abdelrahman T. M. El-Araby K. S. Soliman K. S. Essa E. R. Abo-Ezz 《Pure and Applied Geophysics》2007,164(5):1045-1056
We have developed three different least-squares approaches to determine successively: the depth, magnetic angle, and amplitude
coefficient of a buried sphere from a total magnetic anomaly. By defining the anomaly value at the origin and the nearest
zero-anomaly distance from the origin on the profile, the problem of depth determination is transformed into the problem of
finding a solution of a nonlinear equation of the form f(z)=0. Knowing the depth and applying the least-squares method, the magnetic angle and amplitude coefficient are determined
using two simple linear equations. In this way, the depth, magnetic angle, and amplitude coefficient are determined individually
from all observed total magnetic data. The method is applied to synthetic examples with and without random errors and tested
on a field example from Senegal, West Africa. In all cases, the depth solutions are in good agreement with the actual ones. 相似文献
6.
Maysam Abedi Ahmad Afshar Vahid E. Ardestani Gholam H. Norouzi Caro Lucas 《Acta Geophysica》2010,58(2):317-336
This paper presents a neural network approach to determine 2D inverse modeling of a buried structure from gravity anomaly
profile. The results of the applied neural network method are compared with the results of two other methods, least-squares
minimization and the simple method. Sphere, horizontal cylinder and vertical cylinder and their gravity effects are considered
as the synthetic models and the synthetic data, respectively. The synthetic data are also corrupted with noise to evaluate
the capability of the methods. Then the Dehloran bitumen map in Iran is chosen as a real data application. Anomaly value of
the cross-section, which is taken from the gravity anomaly map of Dehloran bitumen, is very close to those obtained from these
methods. 相似文献
7.
We have developed a least-squares minimization approach to determine the depth and the amplitude coefficient of a buried structure
from residual gravity anomaly profile. This approach is basically based on application of Werner deconvolution method to gravity
formulas due to spheres and cylinders, and solving a set of algebraic linear equations to estimate the two-model parameters.
The validity of this new method is demonstrated through studying and analyzing two synthetic gravity anomalies, using simulated
data generated from a known model with different random error components and a known statistical distribution. After being
theoretically proven, this approach was applied on two real field gravity anomalies from Cuba and Sweden. The agreement between
the results obtained by the proposed method and those obtained by other interpretation methods is good and comparable. Moreover,
the depth obtained by the proposed approach is found to be in very good agreement with that obtained from drilling information. 相似文献
8.
A new interpretative approach is proposed to interpret residual gravity anomaly profiles in order to determine the depth, the amplitude coefficient and the geometric shape factor of simple spherical and cylindrical buried structures. This new approach is based on both Fair function minimization and on stochastic optimization modeling. The validity of this interpretative approach is demonstrated through studying and analyzing two synthetic gravity anomalies, using simulated data generated from a known model with different random noises components and a known statistical distribution. Being theoretically proven, this new approach has been applied on three real field gravity anomalies from Sweden, Senegal and the United States. The agreement between the results obtained by the proposed method and those obtained by other interpretation methods is good and comparable. 相似文献
9.
A geophysical interpretative method is proposed to depth, amplitude coefficient and geometrical shape factor determination
of a buried structure from an observed gravity anomaly related to a cylinder or a sphere-like structure.The method is based
on nonlinearly constrained mathematical modelling and also on stochastic optimization approaches. The proposed interpretative
method first has been tested on theoretical synthetic models with different random errors at a certain depth, where a very
close agreement has been observed between assumed and evaluated parameters. Subsequent field data have been considered for
which the interpreted results by other methods are available for comparison. The agreement between the obtained results by
the proposed technique and by other geophysical methods is good. A statistical analysis has been also carried out to demonstrate
the accuracy and the precision of the suggested interpretative method. 相似文献
10.
2.5维井间电磁反演在中国东部孤岛油田的应用 总被引：3，自引：1，他引：2
In this study, we present a practical technique of transforming cross-hole EM data into the inter-well resistivity distribution. The a priori information constraint is incorporated into an iterative regularized inversion procedure and a variable roughness is added into the inversion process. Finite element approximation based on a two and a half-dimensional （2.5D） model has been developed for the forward problem and the ＂pseudo-forward＂ problem needed for constructing the sensitivity matrix and synthetic data set. The regularized least-squares inversion scheme, constrained with the a priori information obtained from well logs, was adopted to reconstruct the inter-well resistivity profile from two synthetic electromagnetic data sets and field data acquired in the Gudao Oil Field, East China. The partial derivatives of the sensitivity matrix were computed by the adjoint equation based on the reciprocity principle. Inversion results of the synthetic and field data examples suggest that our method is robust and stable in the presence of random noise in the field data and can be used for cross-hole EM field data interpretation. 相似文献
11.
We have developed a least‐squares minimization approach to determine simultaneously the shape (shape factor) and the depth of a buried structure from self‐potential (SP) data. The method is based on computing the standard deviation of the depths determined from all moving‐average residual anomalies obtained from SP data, using filters of successive window lengths for each shape factor. The standard deviation may generally be considered a criterion for determining the correct depth and shape factor of the buried structure. When the correct shape factor is used, the standard deviation of the depths is less than the standard deviations computed using incorrect shape factors. This method is applied to synthetic data with and without random errors, complicated regionals and interference from neighbouring sources, and is tested on a known field example from Turkey. In all cases, the shape and depth solutions obtained are in a good agreement with the actual values. 相似文献
12.
A geophysical interpretative method is proposed to depth, amplitude coefficient (effective magnetization intensity), and index
parameter (effective magnetization inclination) determination of a buried structure from magnetic field data anomaly due to
a fault, a thin dike or a sphere-like structure. The method is based on the nonlinearly constrained mathematical modelling
and also on the stochastic optimization approaches. The proposed interpretative method was first tested on a theoretical synthetic
model with different random errors, where a very close agreement was obtained between the assumed and the evaluated parameters.
The validity of this method was also tested on practical field data taken from United States, Australia, India and Brazil,
where available magnetic data existed and were previously analyzed by different interpretative methods. The agreement between
the results obtained by our developed method and those obtained by the other geophysical methods is good. 相似文献
13.
—?In this paper, a Cellular Neural Network (CNN) has been applied to a magnetic regional/residual anomaly separation problem. CNN is an analog parallel computing paradigm defined in space and characterized by the locality of connections between processing neurons. The behavior of the CNN is defined by the template matrices A, B and the template vector I. We have optimized weight coefficients of these templates using Recurrent Perceptron Learning Algorithm (RPLA). The advantages of CNN as a real-time stochastic method are that it introduces little distortion to the shape of the original image and that it is not effected significantly by factors such as the overlap of power spectra of residual fields. The proposed method is tested using synthetic examples and the average depth of the buried objects has been estimated by power spectrum analysis. Next the CNN approach is applied to magnetic data over the Golalan chromite mine in Elazig which lies East of Turkey. This area is among the largest and richest chromite masses of the world. We compared the performance of CNN to classical derivative approaches. 相似文献
14.
This study proposes the use of multi-layer perceptron neural networks (MLPNN) to invert dispersion curves obtained via multi-channel analysis of surface waves (MASW) for shear S-wave velocity profile. The dispersion curve used in inversion includes the fundamental-mode dispersion data. In order to investigate the applicability and performance of the proposed MLPNN algorithm, test studies were performed using both synthetic and field examples. Gaussian random noise with a standard deviation of 4 and 8% was added to the noise-free test data to make the synthetic test more realistic. The model parameters, such as S-wave velocities and thicknesses of the synthetic layered-earth model, were obtained for different S/N ratios and noise-free data. The field survey was performed over the natural gas pipeline, located in the Germencik district of Ayd?n city, western Turkey. The results show that depth, velocity, and location of the embedded natural gas pipe are successfully estimated with reasonably good approximation. 相似文献
15.
Subsalt exploration for oil and gas is attractive in regions where 3D seismic depth-migration to recover the geometry of a salt base is difficult. Additional information to reduce the ambiguity in seismic images would be beneficial. Gravity data often serve these purposes in the petroleum industry. In this paper, the authors present an algorithm for a gravity inversion based on Tikhonov regularization and an automatically regularized solution process. They examined the 3D Euler deconvolution to extract the best anomaly source depth as a priori information to invert the gravity data and provided a synthetic example. Finally, they applied the gravity inversion to recently obtained gravity data from the Bandar Charak (Hormozgan, Iran) to identify its subsurface density structure. Their model showed the 3D shape of salt dome in this region. 相似文献
16.
《Journal of Atmospheric and Solar》2000,62(8):685-693
Hourly foF2 data from over 100 ionosonde stations during 1967–89 are examined to quantify F-region ionospheric variability, and to assess to what degree the observed variability may be attributed to various sources, i.e., solar ionizing flux, meteorological influences, and changing solar wind conditions. Our findings are as follows. Under quiet geomagnetic conditions (Kp<1), the 1-σ (σ is the standard deviation) variability of Nmax about the mean is approx. ±25–35% at ‘high frequencies’ (periods of a few hours to 1–2 days) and approx. ±15–20% at ‘low frequencies’ (periods approx. 2–30 days), at all latitudes. These values provide a reasonable average estimate of ionospheric variability mainly due to “meteorological influences” at these frequencies. Changes in Nmax due to variations in solar photon flux, are, on the average, small in comparison at these frequencies. Under quiet conditions for high-frequency oscillations, Nmax is most variable at anomaly peak latitudes. This may reflect the sensitivity of anomaly peak densities to day-to-day variations in F-region winds and electric fields driven by the E-region wind dynamo. Ionospheric variability increases with magnetic activity at all latitudes and for both low and high frequency ranges, and the slopes of all curves increase with latitude. Thus, the responsiveness of the ionosphere to increased magnetic activity increases as one progresses from lower to higher latitudes. For the 25% most disturbed conditions (Kp>4), the average 1-σ variability of Nmax about the mean ranges from approx. ±35% (equator) to approx. ±45% (anomaly peak) to approx. ±55% (high-latitudes) for high frequencies, and from approx. ±25% (equator) to approx. ±45% (high-latitudes) at low frequencies. Some estimates are also provided on Nmax variability connected with annual, semiannual and 11-year solar cycle variations. 相似文献
17.
E. M. Abdelrahman H. S. Saber K. S. Essa M. A. Fouda 《Pure and Applied Geophysics》2004,161(2):399-411
We have developed a least-squares minimization approach to depth determination of a buried ore deposit from numerical horizontal gradients obtained from self-potential (SP) data using filters of successive window lengths (graticule spacings). The problem of depth determination from SP gradients has been transformed into the problem of finding a solution to a nonlinear equation of the form f(z)=0. Formulas have been derived for vertical and horizontal cylinders and spheres. Procedures are also formulated to estimate the electrical dipole moment and the polarization angle. The method is applied to synthetic data with and without random noise. Finally, the validity of the method is tested on two field examples. In both cases, the depth obtained is found to be in a very good agreement with that obtained from drilling information. 相似文献
18.
A new method is proposed to interpret magnetic anomalies due to a thin dike, a sphere, and a fault like structure, where depth, horizontal location, effective magnetization intensity and effective magnetization inclination of a buried structure are simultaneously obtained. The proposed method is based on Fair function minimization and also on stochastic optimization modeling. This new technique was firstly tested on a theoretical synthetic data randomly generated by a chosen statistical distribution from a known model with different random noises components. This mathematical simulation shows a very close agreement between the assumed and the estimated parameters. The applicability and validity of this method are thereafter applied to magnetic anomaly data taken from United States, Australia, India, and Brazil. The agreement between the results obtained by the new method and those obtained by other interpretative methods is good and comparable. Moreover, the depth obtained by such a method is found to be in high accordance with that obtained from drilling information. 相似文献
19.
Maurizio Fedi 《Pure and Applied Geophysics》1990,134(3):451-471
The estimation of the depth to the top and bottom of a magnetic source from magnetic data defines a nonlinear inverse problem, while the evaluation of the distribution of magnetization determines a linear inverse problem. In this paper, these interpretation problems are resolved in the continuous case of 21/2D magnetized bodies with lateral magnetization variations. A formulation of the magnetic problem accounting for different directions of remanent and total magnetization vectors and including a more general definition of apparent susceptibility is presented. Differences between 2D and 21/2D formulations are stressed, as regards the anomaly amplitude, shape and zero-level.In order to utilize well-known continuous linear inverse methods, Fréchet derivatives of the data functionals with respect to the depth of the source top and bottom, are analytically described. Thus, using the spectral expansion inverse method (Parker, 1977) and linearizing the problem at several steps of an iterative process, the source depth is obtained within a few iterations, although the starting model is distant from the final solution. The interpretation of an anomaly in the Italian region shows the usefulness of the method. 相似文献
20.
For outcropping bodies an approximate direct interpretation of the associated gravity anomaly is generally obtained with the flat plate formula. Results can be significantly improved if the causative body is approximated by a bell shape instead of a flat plate. A set of parameter curves allows the conversion to depth data. The validity of the method is borne out by synthetic models and by field examples in a Nevada valley with Tertiary and in the Los Angeles Basin. The method provides structural definition more accurate than can be obtained with the flat plate formula, particularly in the case of narrow anomalies. 相似文献