Full transmitter waveform transient electromagnetic modeling and inversion for soundings over coal measures

Asten, Michael

doi:10.1190/1.1442302

Cited by 39 publications

(16 citation statements)

References 16 publications

(19 reference statements)

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“…Attention has been paid mainly to investigations of the dependence of high conducting target signal on the width of the transmitter pulse (e.g., Smith, 1998;Liu, 1998). A phenomenon similar to the frequency dependence was discussed by Asten (1987) based on a full transmitter waveform consideration. It was shown that the effect of the repetitive transmitter waveform is severe on coil recordings over highly conductive ground.…”

Section: Field Trialsmentioning

confidence: 99%

Peculiarities of SQUID magnetometer application in TEM

et al. 2002

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Due to progress in high-temperature superconductor (HTS) technology, research in the application of superconducting quantum interference devices (SQUIDs) in time-domain transient electromagnetics (TEM) has intensified. Several TEM systems using HTS SQUIDs have been developed and tested in numerous field trials. In this paper, the reliability of SQUID TEM data is investigated by comparison with commonly used induction-coil data. Generally, a good agreement between SQUID and coil TEM data was found. However, two effects were observed with the SQUID TEM system which were not visible in coil measurements. The first effect is a "frequency dependence": the response signal measured by the SQUID depends on the base frequency of the transmitter signal, decaying faster for higher frequencies. The second effect is a "zero-crossover": the SQUID response data becomes negative for late times. We propose a model for magnetometer TEM measurements that provides a possible explanation for these two effects. This model takes into account remnant responses induced in the ground by repetitive transmitter signals. Our simulations of coil and magnetometer responses show that, at moderately conducting ground, the influence of remnant responses is negligible in coil recordings, whereas it leads to a typical frequency dependence of magnetometer recordings. We show also that the influence of remnant responses may lead to the sign reversal of magnetometer data over highly conducting ground structures. To optimize magnetometer TEM measurements, it is advantageous to use lower transmitter frequencies than typical frequencies used for induction coil measurements. A recalculation of the original ground response on the basis of the proposed model may also be of advantage.

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Section: Field Trialsmentioning

confidence: 99%

Peculiarities of SQUID magnetometer application in TEM

et al. 2002

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“…In addition to the subsurface resistivities the earth response depends on the transmitter waveform. Asten (1987) shows that modeling of the full transmitter waveform is crucial to the inversion result. In the subsequent equations, B denotes magnetic field.…”

Section: Lp Filters In the Forward Responsesmentioning

confidence: 99%

Optimized Model Resolution Using Low Pass Filters in TDEM Soundings

Auken¹,

Sørensen²,

Thomsen³

et al. 2000

Symposium on the Application of Geophysics to Engineering and Environmental Problems 2000

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INTRODUCTIONIn the time domain electromagnetic (TDEM) method it has been common practice to model the current waveform of the transmitted signal, but the effect of the instrument transfer function has been neglected. In Effersar et al. (1999) it was shown that inverting TDEM data without taking into account the system transfer function in the forward modeling scheme lead to an erroneous description of the shallow part on the geophysical/geological model. The degree of error is very dependent of the near-surface resistivity of the model. High resistivity models leads to distinct but localized errors at very early time gates, whereas the effect from models with low to intermediate resistivities is "smeared" out over a larger time interval.

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“…sometimes assumed to be identical to that obtained from a step function, but corrections for repetitive waveform are now routinely applied (e.g., ASTEN, 1987). The repeated pulses allow coherent stacking of repeated transients, thus reducing noise levels.…”

Section: Depth Of Investigation Of Pulsed Sourcesmentioning

confidence: 99%

An Investigation of Energy Storage Technology for Deep Electromagnetic Exploration.

Spies

1993

J. geomagn. geoelec

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Stationary and portable magnetohydrodynamic (MHD) generators are used in the Soviet Union for deep crustal electromagnetic soundings to depths of tens of kilometers. MHD sources produce tens of megawatts of power and transmit tens of thousands of amperes, but can only be fired at infrequent intervals. An alternative method of attaining a high signal-tonoise ratio is to transmit multiple low-power pulses and stack the repeated signals for some period of time. Energy may be also be stored during the transmitter off time and released in a narrow pulse, a technology known as energy storage or pulse-compression.Varying the pulse width has two opposing effects on the signal-to-noise ratio (SNR). As the transmitter pulse width is increased the received signal increases, but the number of transients that can be stacked in a given period of time decreases. The optimum ratio of transmitter on-time to off-time is 1 for near-zone soundings (source-receiver separation less than the depth of investigation), increasing somewhat for large source-receiver separations.Analysis of signal-to-noise ratio (SNR) demonstrates that there are disadvantages in employing high-power sources such as MHD generators which can not deliver repetitive pulses. Low-power conventional transmitter technology, with signal stacking and adaptive noise cancellation at the receiver, can result in superior results at a much lower cost. In addition, energy storage or pulse-compression technology appears to offer relatively little advantage, and only a moderate gain in SNR is achieved.

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Full transmitter waveform transient electromagnetic modeling and inversion for soundings over coal measures

Cited by 39 publications

References 16 publications

Peculiarities of SQUID magnetometer application in TEM

Peculiarities of SQUID magnetometer application in TEM

Optimized Model Resolution Using Low Pass Filters in TDEM Soundings

An Investigation of Energy Storage Technology for Deep Electromagnetic Exploration.

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