DOWNWARD CONTINUATION USING THE MEASURED VERTICAL GRADIENT

Geophysics ◽  
1971 ◽  
Vol 36 (3) ◽  
pp. 609-612 ◽  
Author(s):  
John Ackerman
Keyword(s):  
Magnetic Field ◽  
Integral Equation ◽  
Direct Method ◽  
Short Note ◽  
Taylor Series Expansion ◽  
Vertical Gradient ◽  
Downward Continuation ◽  
Total Field ◽  
Continuation Problem ◽  
Gradient Measurement

The availability of two independent measured quantities, the total magnetic field and the vertical gradient of the total field, allows a solution to the downward continuation problem not heretofore practical. The method proposed in this short note uses the Laplace equation and a Taylor series expansion but does not require the numerical solution of an integral equation derived from potential theory. Evjen (1937) discussed the use of this technique for the gravitational field; however, he did not advocate the method because of the practical difficulties involved in making the gradient measurement. It is the purpose of my note to point out the utility of this direct method and to discuss the details of its application to airborne gradiometer survey data now being collected.

A comparison of methods for approximating the vertical gradient of one‐dimensional magnetic field data

Geophysics ◽  
1986 ◽  
Vol 51 (9) ◽  
pp. 1725-1735 ◽  
Author(s):  
J. W. Paine
Keyword(s):  
Magnetic Field ◽  
Fourier Transform ◽  
Field Data ◽  
Total Error ◽  
Vertical Gradient ◽  
Magnetic Data ◽  
Total Field ◽  
One Dimensional ◽  
Convolution Filter ◽  
Principal Factors

The vertical gradient of a one‐dimensional magnetic field is known to be a useful aid in interpretation of magnetic data. When the vertical gradient is required but has not been measured, it is necessary to approximate the gradient using the available total‐field data. An approximation is possible because a relationship between the total field and the vertical gradient can be established using Fourier analysis. After reviewing the theoretical basis of this relationship, a number of methods for approximating the vertical gradient are derived. These methods fall into two broad categories: methods based on the discrete Fourier transform, and methods based on discrete convolution filters. There are a number of choices necessary in designing such methods, each of which will affect the accuracy of the computed values in differing, and sometimes conflicting, ways. A comparison of the spatial and spectral accuracy of the methods derived here shows that it is possible to construct a filter which maintains a reasonable balance between the various components of the total error. Further, the structure of this filter is such that it is also computationally more efficient than methods based on fast Fourier transform techniques. The spacing and width of the convolution filter are identified as the principal factors which influence the accuracy and efficiency of the method presented here, and recommendations are made on suitable choices for these parameters.

THE GEOMAGNETIC GRADIOMETER

Geophysics ◽  
1967 ◽  
Vol 32 (5) ◽  
pp. 877-892 ◽  
Author(s):  
Howard A. Slack ◽  
Vance M. Lynch ◽  
Lee Langan
Keyword(s):  
Magnetic Field ◽  
Vertical Gradient ◽  
Diurnal Variations ◽  
Resolving Power ◽  
Magnetic Intensity ◽  
Geophysical Prospecting ◽  
Total Field ◽  
Optically Pumped ◽  
Magnetic Gradient ◽  
The Difference

The geomagnetic gradiometer is a new geophysical prospecting tool which measures directly the vertical gradient of the earth’s magnetic field and the total field intensity. The system is composed of two simultaneously recording, optically pumped and monitored magnetometer sensors suspended from a helicopter. The sensors are separated vertically by a known distance so that the magnetic gradient can be determined from the difference in total magnetic intensity between the two sensors. Since the gradient is measured directly, the gradiometer allows geophysicists to make better use of LaPlace’s and Euler’s equations. The gradiometer increases the value of magnetic prospecting by: (1) greatly increasing resolving power, (2) discriminating between intrabasement and suprabasement anomalies, and (3) eliminating problems caused by diurnal variations.

Prominence height and vertical gradient in magnetic field

2000 ◽  
Vol 26 (5) ◽  
pp. 322-327 ◽  
Author(s):  
B. P. Filippov ◽  
O. G. Den
Keyword(s):  
Magnetic Field ◽  
Vertical Gradient

Magnetocaloric Effect in Ni-Mn-Ga and Ni-Co-Mn-In Heusler Alloys

2009 ◽  
Vol 1200 ◽  
Author(s):  
Vasiliy Buchelnikov ◽  
Sergey Taskaev ◽  
Mikhail Drobosyuk ◽  
Vladimir Sokolovskiy ◽  
Viktor Koledov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetocaloric Effect ◽  
Curie Point ◽  
Direct Method ◽  
Heusler Alloys ◽  
Field Change ◽  
Adiabatic Temperature Change ◽  
Magnetic Field Change ◽  
A Direct Method ◽  
The Magnetic Field

AbstractThe positive magnetocaloric effect (MCE) in the vicinity of the Curie point in Ni2+xMn1-xGa (x=0.33, 0.36, 0.39) Heusler alloys and the negative and positive MCE near the metamagnetostructural (MMS) transition and the Curie point, respectively, in Ni45Co5Mn36.5In13.5 Heusler alloy has been measured by a direct method. For the magnetic field change ΔH = 2 T, the maximal adiabatic temperature change ΔTad at the Curie point in Ni2+xMn1-xGa alloys is larger than 0.6 K. For Ni45Co5Mn36.5In13.5 alloy, the maximal value of ΔTad = 1.68 K (for the same magnetic field change, ΔH = 2 T) is observed at the MMS phase transition temperature.

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