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M. H. Loke

Bio: M. H. Loke is an academic researcher from University of Birmingham. The author has contributed to research in topics: Least squares. The author has an hindex of 1, co-authored 1 publications receiving 515 citations.
Topics: Least squares

Papers
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Journal ArticleDOI
TL;DR: In this article, a smoothness-constrained least square method is used to produce a 2D subsurface model free of distortions in the apparent resistivity pseudosection caused by the electrode array geometry used.
Abstract: A fast technique for the inversion of data from resistivity tomography surveys has been developed. This technique is based on the smoothness-constrained, least-squares method, and it produces a 2-D subsurface model that is free of distortions in the apparent resistivity pseudosection caused by the electrode array geometry used. A homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically. Tests with a variety of models and data from field surveys show that this technique is insensitive to random noise, provided a sufficiently large damping factor is used, and that it can resolve structures that cause overlapping anomalies in the pseudosection. On a 33 MHz 80486DX microcomputer, it takes about 5 s to process a single data set.

568 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a smoothness-constrained least-squares method was used for the interpretation of data from resistivity tomography surveys on an 80486DX microcomputer.
Abstract: A fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer. This technique is based on the smoothness-constrained least-squares method and it produces a two-dimensional subsurface model from the apparent resistivity pseudosection. In the first iteration, a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically. For subsequent iterations, a quasi-Newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times, respectively, compared to the conventional least-squares method. Tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly. This technique takes about one minute to invert a single data set on an 80486DX microcomputer.

2,181 citations

01 Jan 1996
TL;DR: In this article, a smoothness-constrained least-squares method was used for the interpretation of data from resistivity tomography surveys on an 80486DX microcomputer.
Abstract: A fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer. This technique is based on the smoothness-constrained least-squares method and it produces a two-dimensional subsurface model from the apparent resistivity pseudosection. In the first iteration, a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically. For subsequent iterations, a quasi-Newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times, respectively, compared to the conventional least-squares method. Tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly. This technique takes about one minute to invert a single data set on an 80486DX microcomputer.

1,997 citations

Journal ArticleDOI
TL;DR: In this article, numerical simulations are used to compare the resolution and efficiency of 2D resistivity imaging surveys for 10 electrode arrays, including pole-pole (PP), pole-dipole (PD), half-Wenner (HW), Wenner-α (WN), Schlumberger (SC), dipole-dipsole (DD), WenNER-β (WB), γ -array (GM), multiple or moving gradient array (GD) and midpoint-potential-referred measurement (MPR) arrays.
Abstract: Numerical simulations are used to compare the resolution and efficiency of 2D resistivity imaging surveys for 10 electrode arrays. The arrays analysed include polepole (PP), pole-dipole (PD), half-Wenner (HW), Wenner-α (WN), Schlumberger (SC), dipole-dipole (DD), Wenner-β (WB), γ -array (GM), multiple or moving gradient array (GD) and midpoint-potential-referred measurement (MPR) arrays. Five synthetic geological models, simulating a buried channel, a narrow conductive dike, a narrow resistive dike, dipping blocks and covered waste ponds, were used to examine the surveying efficiency (anomaly effects, signal-to-noise ratios) and the imaging capabilities of these arrays. The responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust (L1-norm) inversion and smoothness-constrained least-squares (L2-norm) inversion for the five synthetic models. The results show the following. (i) GM and WN are less contaminated by noise than the other electrode arrays. (ii) The relative anomaly effects for the different arrays vary with the geological models. However, the relatively high anomaly effects of PP, GM and WB surveys do not always give a high-resolution image. PD, DD and GD can yield better resolution images than GM, PP, WN and WB, although they are more susceptible to noise contamination. SC is also a strong candidate but is expected to give more edge effects. (iii) The imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi-electrode layout within the tested ranges. (iv) The robust inversion generally gives better imaging results than the L2-norm inversion, especially with noisy data, except for the dipping block structure presented here. (v) GD and MPR are well suited to multichannel surveying and GD may produce images that are comparable to those obtained with DD and PD. Accordingly, the GD, PD, DD and SC arrays are strongly recommended for 2D resistivity imaging, where the final choice will be determined by the expected geology, the purpose of the survey and logistical considerations.

731 citations

Journal ArticleDOI
TL;DR: There have been major improvements in instrumentation, field survey design and data inversion techniques for the geoelectrical method over the past 25 years as mentioned in this paper, which has made it possible to conduct large 2D, 3D and even 4D surveys efficiently to resolve complex geological structures that were not possible with traditional 1-D surveys.

702 citations