World Applied Sciences Journal 27 (5): 684-687, 2013
ISSN 1818-4952
© IDOSI Publications, 2013
DOI: 10.5829/idosi.wasj.2013.27.05.484
The Application of Pole-Pole Array for The Detection of
Shallow Structures Case of Studies: South West of Tehran: Iran
1
Hamid Reza Samadi and 2Mohammad Reza Samadi
H.D in Geophysics, Ardestan Branch, Islamic Azad University, Ardestan, Iran
Member of Young Researchers Club, Bafgh Branch, Islamic Azad University, Bafgh, Iran
1
2
Abstract: Geoelectric measurements are nowadays an indispensible tool for investigating the shallow
subsurface because the deduced conductivity distribution often provides valuable information for
environmental, hydro geological and engineering applications. Although the geoelectric equipment has
developed rapidly over the last few decades, most geoelectric surveys are still based on 2D surveying strategies
involving conventional co-linear electrode configurations. Although this approach often provides useful
subsurface information, it may lead to serious misinterpretations in the presence of pronounced 3D subsurface
features. At sites with complex resistivity structure, the 2-D assumption may introduce significant error and the
resulting 2-D images can contain significant distortions. Three-dimensional electrical resistivity can be a
practical tool for resolution of complex subsurface heterogeneity. Perhaps the most important reason though,
why application of 3D geoelectric surveys are not yet well established, is the lack of appropriate 3D
experimental design strategies. 3D geoelectric surveying typically requires a large number of electrode positions
to be occupied at the grid points of the rectangular area under investigation. This number is usually much larger
than the number of electrodes available. Resistivity images are created by inverting hundreds to thousands of
individual resistivity measurements in order to produce an approximate model of the subsurface resistivity.
In this paper, the objective is the study over shallow structures using 3D pole-pole array. The site is situated
in Shahriar County which is located 22 km to the southwest of Tehran in Iran. Due to technical limitations, the
number of current and potential electrodes was limited in the field. Therefore, the choice of the appropriate array
for the survey which depends upon optimizing resolution capabilities and the signal-to-noise ratio was crucial.
The survey was conducted in a 3D pole-pole survey with an electrode spacing of 25 cm covering 1.5 m by 1.5
m area over a rectangular cubic box made of aluminum with dimensions of one and a half meters in length and
twenty-five cm in width and height. After data acquisition, resistivity data was inverted with the RES3DINV
program and the vertical and horizontal sections were provided. Then a 3D plot of subsurface layers was
obtained with the Slicer/Dicer program. The results indicate high ability of this method in order to detect
Shallow Structures.
Key words: 3D Pole-Pole array
Shallow Structures
RES3DINV
INTRODUCTION
the investigated structures [3, 4]. In this article the
sensitivity of a geoelectrical modeling technique is
analyzed to image a 3D shallow structure. The objective
is the study over shallow structures using 3D pole-pole
array [2, 5]. The site is situated in Shahriar County which
is located 22 km to the southwest of Tehran in Iran. Due
to technical limitations, the number of current and
potential electrodes was limited in the field. Therefore,
the choice of the appropriate array for the survey which
Geoelectrical methods are powerful tools in
environmental and geotechnical investigations. There is
a broad breath of applications for geoelectrical surveys.
Such surveys would allow a precise characterization of
lateral and vertical resistivity variations [1]. The choice of
a particular array can make a substantial difference to the
results, also depending on the geometry and resistivity of
Corresponding Author:
Slicer/Dicer program
Hamid Reza Samadi, H.D in Geophysics, Ardestan Branch, Islamic Azad University, Ardestan, Iran.
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World Appl. Sci. J., 27 (5): 684-687, 2013
width and height (Figures 1, 2 and 3) which was buried at
the depth of 1 meter.
Data Acquisition Using 3D Pole-Pole Array: In this
study, a 3D pole-pole array is used. The number of datum
point is 84. In the measurements sequence, each electrode
in turn was used as a current electrode and the potentials
measurements sequence, each electrode in turn was used
as a current electrode and the potentials measurements
were made at the electrodes along the horizontal and
vertical directions. Due to reciprocity, it was only
necessary to measure the potentials at the electrodes with
a higher index number than the current electrode. Since in
practice, the ideal pole-pole array with only one current
and one potential electrode does not exist, to approximate
the pole-pole array, the second current and potential
electrode (C2 and P2) must be placed at a distance which
is at least 10 times the maximum separation between c1 and
p1 electrodes used in the survey to insure that the error is
less than 5%. So in this survey, the electrode p2 was
placed at 7.5 meters and the electrode c2 was placed at
15 meters far from the network.
Fig. 1:
Horizontal Section: After applying the inversion, 6
sections were introduced by RES3DINVERS software as
horizontal sections (Figure 4). These sections cover from
the surface to the depth of 1.94 meters As the figure
shows, from the surface to the depth of 1.18 meters,
resistivity changes from 97 to122 ohm meter. From the
depth of 1.18 meters to 1.53 meters, resistivity changes
from 48.9 t77.2 ohm meters and from the depth of 1.53
meters to 1.94 meters, resistivity changes from 24.7 to61.5
ohm meter.
Fig. 2:
Vertical Sections: In Figure 5, vertical sections which are
parallel to the anomaly are shown. It is proved that in line
which is parallel with an anomaly, resistivity changes are
very minor and the sections show this fact as well Vertical
sections which are perpendicular to the anomaly are
shown in figure 6. It is proved that in the line which is
perpendicular to an anomaly, resistivity changes are
totally clear which these sections confirm this fact as well.
Fig. 3:
D Image of Subsurface Layers Using Slicer/Dicer
Program: RES3DINV software enables the user to get the
output under the extension gm after the inversion. The file
which has this suffix is used as an input for Slicer/Dicer
program to produce a 3 dimensional structure. Figure 7,
shows a 3D image of subsurface structure which has been
produced by this program.
depends upon optimizing resolution capabilities and the
signal-to-noise ratio was crucial. The survey was
conducted in a 3D pole-pole survey with an electrode
spacing of 25 cm covering 1.5 m by 1.5 m area over a
rectangular cubic box made of aluminum with dimensions
ofone and a half meters in length and twenty-five cm in
685
World Appl. Sci. J., 27 (5): 684-687, 2013
Fig. 4:
Fig. 5:
Fig. 6:
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World Appl. Sci. J., 27 (5): 684-687, 2013
Fig. 7:
DISCUSSION AND CONCLUSION
REFERENCES
This array has the widest horizontal coverage and the
deepest depth of investigation in comparison with the
other common arrays so the pole-pole array might be a
suitable choice for surveys with small electrode spacing
and when good horizontal coverage is required. In a 3D
survey, a large amount of data point is read so the user
can get an image of subsurface layers with high quality
and less noise. Nowadays, considerable researches in the
field of geo electric exploration have been done. However,
because of the large number of data points, operation time
and the cost are high but it is expected that in a near
future with development in multi-channels measuring
devices, which enables the users to read several data
points simultaneously and the progress in interpretation
software, that enables the users to have the interpretation
of a lot of data points (more than 8000 data), the
mentioned problems will be solved and this method will be
a suitable alternative for geo electric 2D surveys. With
modern multi-electrode equipment and continuous
systems, data are measured in many profile configurations
so that lateral and vertical resistivity variation can be
determined through data inversion. Measurements of
pole-pole array are widely applied to archaeological
surveys; they are probably suitable for a greater number
of sites than any other technique.
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