Field test of the new melis frequency EM system

Valla, Pierre G.; Gasnier, S.; Pottecher, G.

doi:10.1190/1.1892956

Cited by 2 publications

(3 citation statements)

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“…This is understandable for conventional CSAMT, since the electrical field does not vanish at infinity in the case of a 2D current injection wire. However, for a loop type of source such as that of the MClos method (Valla et al 1986), such a difficulty does not occur.…”

Section: D M a G N E T I C D I P O L E Sourcementioning

confidence: 99%

“…1). This is the basis of the newer Mklos method (Valla, Gasnier and Pottecher 1986;Valla 1991a). For mineral exploration, the p' type of Mtlos measurement is usually preferred: since it is based only on magnetic fields, it avoids the 'static shift' effect often present in classical controlled-source audio-magnetotelluric techniques (CSAMT) or p" type of measurements.…”

Section: Introductionmentioning

confidence: 99%

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FIXED LOOP SOURCE EM MODELLING RESULTS USING 2D FINITE ELEMENTS¹

Valla

1992

Geophysical Prospecting

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Among electromagnetic sounding techniques, the Mélos method possesses the specific feature of including an apparent resistivity computation. This acts as a normalizing scheme so that 2D modelling results can be obtained without accounting for a true 3D source. However, in order to get reliable numerical modelling results for a 2D magnetic dipole source, improved algorithms are required in order to apply the standard finite‐element technique: quadratic basis functions must be used in place of linear basis functions, and a more sophisticated method than conventional ones is necessary for properly solving the resulting system of linear equations. Such modelling results have been used to study theoretical responses for the Mélos method in the search for conductive bodies in mineral exploration. Two sets of models are presented and discussed. They show that the typical Mélos response to a conductive target is a bipolar anomaly on the apparent resistivity pseudo‐section, with a conductive pole at low frequency which is centred above the target.

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Section: D M a G N E T I C D I P O L E Sourcementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

FIXED LOOP SOURCE EM MODELLING RESULTS USING 2D FINITE ELEMENTS¹

Valla

1992

Geophysical Prospecting

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“…This apparent-resistivity concept was based on the amplitude ratio of different components of the radiated field. The same concept was used by Valla, Gasnier and Pottecher (1986). Another apparent-resistivity concept based on the amplitude ratio of measured field components was described by Aittoniemi, Rajala and Sarvas (1987).…”

Section: Introductionmentioning

confidence: 99%

An apparent‐resistivity concept for low‐frequency electromagnetic sounding techniques

Kruk

Meekes

Berg

et al. 2000

Geophysical Prospecting

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Apparent resistivity is a useful concept for initial quickscan interpretation and quality checks in the field, because it represents the resistivity properties of the subsurface better than the raw data. For frequency‐domain soundings several apparent‐resistivity definitions exist. One definition uses an asymptote for the field of a magnetic dipole in a homogeneous half‐space and is useful only for low induction numbers. Another definition uses only the amplitude information of the total magnetic field, although this results in a non‐unique apparent resistivity. To overcome this non‐uniqueness, a complex derivation using two different source–receiver configurations and several magnetic field values for different frequencies or different offsets is derived in another definition. Using the latter theory, in practice, this means that a wide range of measurements have to be carried out, while commercial systems are not able to measure this wide range. In this paper, an apparent‐resistivity concept is applied beyond the low‐induction zone, for which the use of different source–receiver configurations is not needed. This apparent‐resistivity concept was formerly used to interpret the electromagnetic transients that are associated with the turn‐off of the transmitter current. The concept uses both amplitude and phase information and can be applied for a wide range of frequencies and offsets, resulting in a unique apparent resistivity for each individual (offset, frequency) combination. It is based on the projection of the electromagnetic field data on to the curve of the field of a magnetic dipole on a homogeneous half‐space and implemented using a non‐linear optimization scheme. This results in a fast and efficient estimation of apparent resistivity versus frequency or offset for electromagnetic sounding, and also gives a new perspective on electromagnetic profiling. Numerical results and two case studies are presented. In each case study the results are found to be comparable with those from other existing exploration systems, such as EM31 and EM34. They are obtained with a slight increase of effort in the field but contain more information, especially about the vertical resistivity distribution of the subsurface.

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Field test of the new melis frequency EM system

Cited by 2 publications

References 1 publication

FIXED LOOP SOURCE EM MODELLING RESULTS USING 2D FINITE ELEMENTS¹

FIXED LOOP SOURCE EM MODELLING RESULTS USING 2D FINITE ELEMENTS¹

An apparent‐resistivity concept for low‐frequency electromagnetic sounding techniques

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Field test of the new melis frequency EM system

Cited by 2 publications

References 1 publication

FIXED LOOP SOURCE EM MODELLING RESULTS USING 2D FINITE ELEMENTS1

FIXED LOOP SOURCE EM MODELLING RESULTS USING 2D FINITE ELEMENTS1

An apparent‐resistivity concept for low‐frequency electromagnetic sounding techniques

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FIXED LOOP SOURCE EM MODELLING RESULTS USING 2D FINITE ELEMENTS¹

FIXED LOOP SOURCE EM MODELLING RESULTS USING 2D FINITE ELEMENTS¹