Wave tilt of radio waves propagating over a layered ground

Wait, James R.; Nabulsi, K.A.

doi:10.1190/1.1444083

Cited by 5 publications

(7 citation statements)

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“…At frequencies lower than those employed by Nabulsi & Wait (1996) and Stewart et al (1994), displacement currents become weaker and the resolvability of permittivity anomalies within a limited range of possible relative permittivity values deteriorates. Huang & Fraser (2002) (see Section 1.1) estimate a single value of relative permittivity at their highest frequency of 100 kHz, as it is a badly resolved parameter at lower frequencies.…”

Section: Resolvability Of Permittivity Anomaliesmentioning

confidence: 89%

“…Using obliquely incident plane waves in the VHF range (30-300 MHz), Nabulsi & Wait (1996) illustrate that a dielectric layer embedded in a highly resistive host is detectable if its thickness and relative permittivity are sufficiently high.…”

Section: Resolvability Of Permittivity Anomaliesmentioning

confidence: 99%

“…The resolvability of the relative dielectric permittivity from both plane-wave and controlled-source FDEM measurements is assessed by Nabulsi & Wait (1996), Stewart et al (1994), Huang & Fraser (2002) and Persson & Pedersen (2002) with 1-D simulations.…”

Section: Resolvability Of Permittivity Anomaliesmentioning

confidence: 99%

“…Several publications describe the effect of displacement currents on plane‐wave and controlled‐source FDEM responses in the VLF and LF frequency ranges, based on analytic solutions by Wait (1953, 1970) and Wait & Nabulsi (1996) for a 1‐D layered Earth.…”

Section: Introductionmentioning

confidence: 99%

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Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents

Kalscheuer¹,

Pedersen²,

Siripunvaraporn

2008

Geophysical Journal International

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S U M M A R YElectromagnetic surface measurements with the radiomagnetotelluric (RMT) method in the frequency range between 10 and 300 kHz are typically interpreted in the quasi-static approximation, that is, assuming displacement currents are negligible. In this paper, the dielectric effect of displacement currents on RMT responses over resistive subsurface models is studied with a 2-D forward and inverse scheme that can operate both in the quasi-static approximation and including displacement currents.Forward computations of simple models exemplify how responses that allow for displacement currents deviate from responses computed in the quasi-static approximation. The differences become most obvious for highly resistive subsurface models of about 3000 m and more and at high frequencies. For such cases, the apparent resistivities and phases of the transverse magnetic (TM) and transverse electric (TE) modes are significantly smaller than in the quasi-static approximation. Along profiles traversing 2-D subsurface models, sign reversals in the real part of the vertical magnetic transfer function (VMT) are often more pronounced than in the quasi-static approximation. On both sides of such sign reversals, the responses computed including displacement currents are larger than typical measurement errors.The 2-D inversion of synthetic data computed including displacement currents demonstrates that serious misinterpretations in the form of artefacts in inverse models can be made if displacement currents are neglected during the inversion. Hence, the inclusion of the dielectric effect is a crucial improvement over existing quasi-static 2-D inverse schemes. Synthetic data from a 2-D model with constant dielectric permittivity and a conductive block buried in a highly resistive layer, which in turn is underlain by a conductive layer, are inverted. In the quasi-static inverse model, the depth to the conductive structures is overestimated, artefactual resistors appear on both sides of the conductive block and a spurious conductive layer is imaged at the surface.High-frequency RMT field data fromÄvrö, Sweden, are re-interpreted using the newly developed 2-D inversion scheme that includes displacement currents. In contrast to previous quasi-static modelling, the new inverse models have electrical resistivity values comparable to a normal-resistivity borehole log and boundaries between resistive and conductive structures, which correlate with the positions of seismic reflectors.Since many electromagnetic (EM) methods utilize frequencies below 10 kHz, the quasi-static assumption that displacement currents are much smaller than conduction currents (i.e. ω σ with angular frequency ω = 2π f , dielectric permittivity = r 0 , free air permittivity 0 and electrical conductivity σ ) is stipulated and displacement currents are neglected during the data interpretation. For the radiomagnetotelluric (RMT) method, which uses EM fields in the VLF (3-30 kHz) and LF (30-300 kHz) frequency ranges, the validity of the quasi-static assumption is q...

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Section: Resolvability Of Permittivity Anomaliesmentioning

confidence: 89%

Section: Resolvability Of Permittivity Anomaliesmentioning

confidence: 99%

Section: Resolvability Of Permittivity Anomaliesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents

Kalscheuer¹,

Pedersen²,

Siripunvaraporn

2008

Geophysical Journal International

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“…The fundamentals of the model used in this work to generate the wave-tilt data have been investigated for over 60 years [5][6][7][28][29][30][31]. The good agreement between theory and practice has justified many wave-tilt studies involving only synthetic data [7,29,[32][33][34]. Some important theoretical conclusions that were later borne out by field experiments are the following.…”

Section: Simulationsmentioning

confidence: 99%

Robust nonlinear inversion of wave-tilt data

Lopes

Barreto

et al. 1998

Inverse Problems

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A robust method for characterizing homogeneous or layered geophysical media is proposed. It determines the electrical constitutive parameters and the thicknesses of the layers that make up the probed medium by inverting magnetic wave-tilt data collected on or above the ground surface. An algorithm is presented for establishing whether the medium should be considered homogeneous or stratified. An exact analytical solution to the inverse problem of homogeneous media is deduced. The inverse problem of stratified media is solved by a threelayer feedforward neural network. An algorithm is proposed for speeding up the training of the neural network. Compared to the standard back-propagation algorithm, the new algorithm is faster, more robust, and easier to implement both in hardware form and in software form. Also, the new algorithm requires less memory space. Such an algorithm stems from applying a new gradient-based method to the problem of adjusting the free parameters of a feedforward neural network. A versatile network-pruning technique is proposed. It explores the fact that the free parameters of a trained neural network tend to take on values close to their mean. The characteristics of magnetic wave-tilt data are analysed in detail. The insight provided by this analysis helps to properly interpret the results of the inversions.

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Near‐Ground Propagation Mechanisms in Wireless Communications

Michalski

2024

Encyclopedia of RF and Microwave Engineering

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In this chapter, we reexamine the solution of the century‐old Sommerfeld problem of a vertical or horizontal elementary Hertzian dipole antenna radiating over a material half‐space. This classical problem is still relevant to many modern applications, including geophysical prospecting, detection of unexploded ordnance, near‐ground sensors, on‐body networks, surface radar, and cellular wireless communications. To gain more insight into the near‐ground wireless propagation mechanisms, we derive the asymptotic field expressions by using the modified saddle‐point integration method, paying particular attention to the so‐called Norton surface wave and its significance in the total field of the dipole. We also extend the theory to include the effect of a thin, low‐loss overlayer. We illustrate and validate the theoretical developments by numerical results involving on‐surface and elevated transmitter–receiver configurations and different lower half‐space media, including seawater and urban ground, with emphasis on modern high‐frequency applications, where the media losses are relatively small. We also include a brief review of the history of the Sommerfeld half‐space problem with references to the most pertinent literature.

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Wave tilt of radio waves propagating over a layered ground

Cited by 5 publications

References 0 publications

Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents

Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents

Robust nonlinear inversion of wave-tilt data

Near‐Ground Propagation Mechanisms in Wireless Communications

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