Gravity and magnetic data interpretation with non-linear transforms

2011 ◽  
Author(s):  
Caio B. Ferreira ◽  
Carlos A. Mendonca
Keyword(s):  
Data Interpretation ◽  
Magnetic Data ◽  
Linear Transforms ◽  
Gravity And Magnetic ◽  
Non Linear ◽  
Gravity And Magnetic Data

DOWNWARD CONTINUATION AND ITS APPLICATION TO ELECTROMAGNETIC DATA INTERPRETATION

Geophysics ◽  
1966 ◽  
Vol 31 (1) ◽  
pp. 167-184 ◽  
Author(s):  
Amalendu Roy
Keyword(s):  
Wave Equation ◽  
Field Data ◽  
Country Rock ◽  
Data Interpretation ◽  
Downward Continuation ◽  
Magnetic Data ◽  
Body Experience ◽  
Gravity And Magnetic ◽  
Displacement Currents ◽  
Gravity And Magnetic Data

The existing methods of downward continuation were developed primarily for the interpretation of gravity and magnetic data, and, therefore, assume the validity of Laplace’s equation. The data collected in electromagnetic surveys, strictly speaking, obey Maxwell’s wave equation. However, in practice, two approximations are frequently made. First, the effects of displacement currents are neglected in view of the fact that the frequencies used are low. Second, the contribution of the country rock to the measured field is assumed to be nil, as its electrical conductivity is usually much smaller than that of the target body. Experience seems to indicate that these two approximations are permissible in general. It will be seen that, under these two approximations, Maxwell’s wave equation degenerates to that of Laplace, and the existing techniques of continuation become applicable to electromagnetic field data as well. This hypothesis has been tested by using continuation to interpret 20 electromagnetic profiles, involving a variety of theoretical, model, and field data. It has been found that the depths to the tops of the anomaly‐causing bodies can be determined with acceptable accuracy by this method.

Modern Software for Gravity and Magnetic Data Interpretation

1993 ◽  
Author(s):  
A. A. Cheznov ◽  
L.T. Berezhnaya ◽  
U. Telepin ◽  
D. Fedynski
Keyword(s):  
Data Interpretation ◽  
Magnetic Data ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data

Automatic 3-D interpretation of potential field data using analytic signal derivatives

Geophysics ◽  
1997 ◽  
Vol 62 (1) ◽  
pp. 87-96 ◽  
Author(s):  
Nicole Debeglia ◽  
Jacques Corpel
Keyword(s):  
Signal Amplitude ◽  
Vertical Gradient ◽  
Analytic Signal ◽  
Magnetic Data ◽  
Practical Implementation ◽  
Potential Field Data ◽  
Gravity And Magnetic ◽  
Second Derivatives ◽  
Gravity And Magnetic Data ◽  
Derivatives Of

A new method has been developed for the automatic and general interpretation of gravity and magnetic data. This technique, based on the analysis of 3-D analytic signal derivatives, involves as few assumptions as possible on the magnetization or density properties and on the geometry of the structures. It is therefore particularly well suited to preliminary interpretation and model initialization. Processing the derivatives of the analytic signal amplitude, instead of the original analytic signal amplitude, gives a more efficient separation of anomalies caused by close structures. Moreover, gravity and magnetic data can be taken into account by the same procedure merely through using the gravity vertical gradient. The main advantage of derivatives, however, is that any source geometry can be considered as the sum of only two types of model: contact and thin‐dike models. In a first step, depths are estimated using a double interpretation of the analytic signal amplitude function for these two basic models. Second, the most suitable solution is defined at each estimation location through analysis of the vertical and horizontal gradients. Practical implementation of the method involves accurate frequency‐domain algorithms for computing derivatives with an automatic control of noise effects by appropriate filtering and upward continuation operations. Tests on theoretical magnetic fields give good depth evaluations for derivative orders ranging from 0 to 3. For actual magnetic data with borehole controls, the first and second derivatives seem to provide the most satisfactory depth estimations.

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