ABSTRACT
The development of resistivity surveying techniques has been very rapid in the last three decades. Theadvent of automated data acquisition systems, inversion codes, and easy access to powerful and fast computers has tremendously increased the practical applicability of the geophysical method. Geoelectrical resistivity imaging is increasingly being used in environmental, engineering and hydrological investigations as well as geothermal and mineral prospecting, where detailed knowledge
of the subsurface is sought. In this paper, the historical development and basic principles of geoelectrical resistivity surveying techniques are presented. Past researches and on-going developments in the survey designs and field procedures in two-dimensional (2D) and threedimensional (3D) geoelectrical resistivity surveys are discussed. Current development in the acquisition geometry for 3D geoelectrical resistivity imaging data is emphasized.
Scientific Research and Essays Vol. 5(23), pp. 3592-3605, 4 December, 2010
Available online at http://www.academicjournals.org/SRE
ISSN 1992-2248 ©2010 Academic Journals
1. INTRODUCTION
Electrical and electromagnetic (EM) methods have beenimportant in the field of Applied Geophysics for about acentury, particularly for shallow and near-surface investigations. The use of geoelectrical resistivity surveys for investigating subsurface layered media has its origin in 1912 due to the work of Conrad Schlumberger who conducted the first geoelectrical resistivity experiment in the fields of Normandy; and about 1915, a similar idea was developed by Frank Wenner in the United State of American (USA) (Kunetz, 1966). Ever since, geoelectrical resistivity surveying has greatly improved, and has become an important and useful tool in hydrogeological studies, mineral prospecting and mining, as well as in environmental and engineering applications (e.g. Griffiths et al., 1990; Griffiths and Barker, 1993; Dahlin and Loke, 1998; Olayinka, 1999; Olayinka and Yaramanci, 1999; Amidu and Olayinka, 2006; Aizebeokhai et al., 2010).
The classical methods of geoelectrical resistivity surveys have undergone significant changes in the last three decades. The traditional horizontal layering technique for interpreting geoelectrical resistivity data are rapidly being replaced with two-dimensional (2D) and three-dimensional (3D) models of interpretations, especially in complex and heterogeneous subsurface media. Field techniques have advanced from measure-ments made at separate and independent points to automated measuring systems with multi-electrode array along the measurement profiles. Data acquisition was more or less carried out manually till the 1980s, and this is labour intensive and slow, and the quality of the measured data might be poor. A range of fast automated multi-electrode and multi-channel data acquisition systems now exist that allows flexibility in the acquisition of geoelectrical resistivity data (Barker, 1981; Stummer and Maurer, 2001; Auken et al., 2006).
Traditionally, electrical resistivity surveying was limited to either delineating the variation of apparent resistivity over a surface or compiling quasi-2D sections from a rather limited numbers of vertical electrical soundings (VES). The use of multi-electrode/multi-channel systems for data acquisition in geoelectrical resistivity surveys has led to a dramatic increase in field productivity as well as increased quality and reliability of subsurface resistivity information obtained. Initially, multi-electrode systems with manual switching (Barker, 1981) were used before the emergence of computer-controlled multielectrode/multi-channel systems with automatic measurements and data quality control, which has tremendous impact on the quality of the data and the speed with which they are collected. Intelligent multielectrode with built-in-preamplifiers, analog-to-digital converters, and digital transmission lines can now be effectively used for data acquisition. Multi-channel transmitter and receiver systems are now being used in simultaneously carrying out series of measurements (Stummer and Maurer, 2001; Auken et al., 2006).
2. BASIC THEORY OF
GEOELECTRICAL RESISTIVITY SURVEYS
Electrical and
electromagnetic (EM) methods are defined by their frequency of operation,
the origin of the source signals and the manner by which the sources
and receivers are coupled to the ground.
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