The Analysis of EM Wave for Different Media by GPR Technique

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 03 Issue: 01 | Jan-2016 www.irjet.net p-ISSN: 2395-0072
© 2016, IRJET ISO 9001:2008 Certified Journal Page 207
The Analysis of EM Wave for Different Media by GPR Technique
1Randy Pain, 2Dr. M. M. Nordiana, 3Nabila Sulaiman, 3Hazrul Hisham
1 Undergraduate Student, School of Physics, Geophysics Section, Universiti Sains Malaysia, 11800 Penang, Malaysia
2Senior Lecturer, School of Physics, Geophysics Section, Universiti Sains Malaysia 11800 Penang, Malaysia
3Postgraduate Student, School of Physics, Geophysics Section, Universiti Sains Malaysia 11800 Penang, Malaysia
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Abstract - Ground Penetrating Radar (GPR) is a near-
surface geophysical tool with a wide range of
applications such as locating utility, concrete
inspection, archeological and geological studies. GPR is
chosen for this survey for its ability to distinguish
different pattern of electromagnetic (EM) wave that
represents different types of media. This survey was
conducted at the hilly part of Universiti Sains Malaysia
(USM), Pulau Pinang. The survey site features were
known subsurface architecture constructed with three
different kinds of media, they are asphalt, air and
concrete. The aim of this survey is to analyze and
understand the signal of 3 different media. Equipments
used are MALA 250 MHz shielded antenna, MALA ProEx
Control Unit, MALA Monitor XV11, 50 m measuring tape
rope, wheel and optical cable. The results obtained are
enhanced using the RAMAC GroundVision software with
3 types of filter which are band pass, time varying gain
and DC removal. After the enhancement of radargram,
it is exported to ASCII format to be open with Microsoft
Excel. From the Microsoft Excel, the trace of 3 different
types of media is chosen and the graph of amplitude vs
time (ns) is plotted. The results were interpreted
accurately in order to properly assess any feature of the
study particularly the length of period in the first
wavelet of the graph of amplitude vs time (ns) and
comparing it to the actual theory electrical properties
and velocities of the medium. The results showed that
air (53.04 ns) has the lowest period compared to
asphalt and concrete indicating that air has the highest
velocity for EM wave propagation among the three
mediums.
Key Words: EM wave, period, medium, GPR
1. INTRODUCTION
Ground Penetrating Radar (GPR) is one of the geophysical
techniques used to study the subsurface characteristic. It
is a non-destructive method and easy to operate. GPR
produced a radargram during data acquisition that shows
the results for different types of media.
The survey is done to distinguish the electromagnetic
(EM) wave for different media such as asphalt, air and
concrete. The GPR signal as displayed on radargram is
difficult to be interpreted and identified, therefore a few
types of filter needs to be done to make the radargram
image more clearer. Based from the radargram, the signal
will give different values of amplitude and attenuation
properties in relation to the types of media.
In this study, the trace for each type of media is analysed.
The main concerned parameter is the period which can be
related to the velocity of EM wave that travelled through
the different types of media.
2. GPR EQUIPMENTS
The GPR device used in this study is MALA 250 MHz
shielded antenna comprises data acquisition transmitter
and radar receiver. The device used during data
acquisition consists of MALA ProEx Control Unit which
connects the shielded antenna to the MALA Monitor XV11
that displays the radargram. An optical cable is connected
from the control unit to the monitor. A wheel is attached at
the back of the shielded antenna for measuring the
acquisition distance. A rope is used to pull the shielded
antenna while acquiring the data. The data processing
equipment is basically a laptop and suitable software to
visualize, filtering and interpret the radargram. The
procedure of data acquisition was carried out in a line
covering different types of media which are asphalt, air
and concrete. Figure 1 and Table 1 shows the listings of
the GPR equipments.
Figure 1: GPR Equipments.
5
4
3
1
6
7
2

Table 1: Equipment’s list.
No. Name of equipment
1 Rope
2 Optical cable
3 MALA ProEx Control Unit
4 MALA Monitor XV11 with the battery
5 MALA 250 MHz shielded antenna
6 50 m measuring tape
7 Wheel
3. THEORY OF GPR
GPR is a subsurface imaging method that provides high-
resolution information to a depth of typically 0 – 10 m.
Using the wave propagation characteristics of
electromagnetic fields, GPR provides a very high
resolution subsurface mapping method. In many ways,
GPR is the electromagnetic counterpart of seismic
reflection. GPR has a limited exploration depth, so it is not
a tool for all applications. The most detailed information
can be obtained using GPR in electrically resistive where it
is the most effective [1].
A GPR system consists of a few components, as shown in
Figure 2, which emit an EM wave into the ground and
receive the response. A part of the EM wave is reflected
back to the receiver antenna if there is a change in electric
properties in the ground or if there is an anomaly that has
different electrical properties than the surrounding
medium or an object. The system scans the ground to
collect the data at various locations. Then a GPR profile
can be constructed by plotting the amplitude of the
received signals as a function of time and position,
representing a vertical slice of the subsurface. The time
axis can be converted to depth by assuming a velocity for
the EM wave in the subsurface soil [3].
Figure 2: Block diagram of a GPR system [3].
4. STUDY AREA
The study area is located in USM, Pulau Pinang. The line
has a total length of 13 m which consists of different media
like asphalt, air and concrete. The line is divided into three
sections with asphalt from 0 m to 6.7 m, air from 6.7 m to
7.2 m and concrete from 7.2 m to 13 m. The area is on top
of a hill with a flat top which cover the whole line. Figure 3
shows the study area for this survey.
Figure 3: The study area in USM, Pulau Pinang [4].
Figure 4 shows the exact location where GPR is conducted.
GPR is moving from 0 m to 13 m.
Figure 4: Different medium for conducting GPR.
5. METHODOLOGY
GPR survey is based on measuring the EM pulse that is
being transmitted by a transmitter. The wave travels
downward eventually refracted and reflected as it travels
through the subsurface layer or boundary with different
electrical properties and dielectric constant. The wave that
is reflected back to the surface is then captured by the
receiving antenna and recorded on a digital storage device
for later interpretation.
This survey used 250 MHz shielded antenna with
sampling frequency of 2450 MHz. The point interval used
is 0.02 m and antenna separation is 0.31 m. The total
length of the survey line is 13 m, which is measured by a
measuring tape. The shielded antenna is pulled slowly to
make sure there is no wave distortion in display unit. The
Study Area
0m
6.7m
7.2m
13m
Asphalt
Air
Concrete
GPR direction

recorded data is processed using RAMAC GroundVision
and Microsoft Excel. In RAMAC GroundVision software, the
data is filtered using 3 types of filter which are DC
Removal, Time Varying Gain and Band Pass to remove the
noise. The filtered data is exported to ASCII format and is
opened in Microsoft Excel. The different medium
amplitude is chosen to plot graphs of Amplitude vs Time
(ns).
6. RESULTS AND DISCUSSION
There were 3 different types of media which are asphalt (0
– 6.7 m), air (6.7 – 7.2 m) and concrete (7.2 – 13 m). Figure
5 shows the data display from RAMAC GroundVision for
the study area in USM. From Figure 5, trace 122 indicate
asphalt anomaly, trace 389 indicate air anomaly and trace
659 indicate concrete anomaly. Figure 6 shows
understanding of the radargram
The results show the most distinct anomaly at the distance
between 6.7 m to 7.2 m. The anomaly indicates air due to
its difference in dielectric constant (ε = 1) from concrete (ε
= 6 to 8) and asphalt (ε = 3 to 5) as shown in Table 2.
Based on Figure 7 that shows the graph of amplitude vs
time (ns) for asphalt, the period which can be measured
from the graph is 69.36 ns. Figure 8 shows that the period
for air is 53.04 ns and Figure 9 shows the period for
concrete is 65.28 ns. Figure 10 shows the combined
results for air, asphalt and concrete in one graph of
amplitude vs time (ns). The three mediums show similar
graph pattern of amplitude.
The graph from Figure 10 starts to show fluctuation at the
time of 90.42 ns. Based on the previous calculation, the
results state that EM wave for air medium having the
shortest period which tells EM wave for air travelled with
the highest velocity compared to asphalt and concrete.
Both asphalt and concrete have longer period, hence
having a lower velocity than air.
Table 2: Electrical properties of materials [2].
Material Dielectric Velocity (m/µs)
Air 1 300
Concrete 6-8 55-112
Asphalt 3-5 134-173
Figure 5: Data display from RAMAC GroundVision.
Figure 6: Understanding radargram.
Figure 7 shows the EM wave for asphalt medium, from
time 0 ns to approximately 97.92 ns, the amplitude is zero
due to the air wave layer. The maximum amplitude starts
at positive. The wave starts to lose its signal at time 244.8
ns.
Figure 7: Graph of Amplitude vs Time (ns) for asphalt.
Figure 8 shows the EM wave for air medium, from time 0
ns to approximately 102 ns, the amplitude is zero due to
the air wave layer. The amplitude starts to reflect at
negative amplitude. Anomalies where the first reflections
were negative were determined as cavities [5]. In this
case, air is considered as voids. The wave starts to lose its
signal at time 387.6 ns due to loss of energy.
Air wave
Black line: Positive
White line: Negative
Attenuation of wave signals

Figure 8: Graph of Amplitude vs Time (ns) for air.
Figure 9 shows the EM wave for concrete medium, from
time 0 ns to approximately 97.92 ns, the amplitude is zero
due to air wave layer. The maximum amplitude starts at
positive. The wave starts to lose its signal at time 244.8 ns
because of energy loss.
Figure 9: Graph of Amplitude vs Time (ns) for concrete.
Generally, Figure 10 shows the entire EM wave for the 3
different types of media. From previous analysis of each
EM wave based on both parameter of period and signal
amplitude, the EM wave for air medium travelled much
farther than the other media, it also start to attenuate the
slowest compared to others. Both asphalt and concrete
nearly shows the same EM wave pattern, concrete medium
shows slightly high amplitude than asphalt.
Figure 10: Graph of Amplitude vs Time (ns) for the three
different media.
7. CONCLUSIONS
GPR is a powerful diagnostic method for the identification
of signal for different types of media. While GPR is a great
tool, it does not come without its downfalls. Ground
composition, electromagnetic noise in the area, depth of a
feature, and resolution are all factors determining the
effectiveness of GPR profiling. The resultant data should
be interpreted carefully, combining the relevant
information of above ground and subsurface features. This
survey identifies that the air has the shortest value of
period compared to asphalt and concrete indicating that
air has higher velocity than both asphalt and concrete.
ACKNOWLEDGEMENT
The authors thank the technical staffs of the geophysics
laboratory, final year project students and all geophysics
postgraduate students, School of Physics, Universiti Sains
Malaysia for their assistance during the data acquisition.
REFERENCES
[1] Annan, A.P., and Davis, J. L. (1997), Ground
Penetrating Radar—Coming of Age at Last, in Prof. of
the Fourth Decennial International Conf. on Mineral
Exploration, Gubins, AG., ED., Toronto, ON, Canada,
pp. 515-522.
[2] Davis, J. L., and Annan, A. P. (1989), Ground
penetrating radar for high resolution mapping of soil
and rock stratigraphy. Geophysical prospecting, Vol.
37, p. 531-551.
[3] Davis, J. L., and Annan, A. P., 1986. High resolution
sounding using ground probing radar. Geoscience
Canada, Vol. 13(3), p. 205-208.
[4] Kazunori T, J. Iger, H., Seiichiro K. (2012) "Basics
Application of Ground-Penetrating Radar as a Tool
For Monitoring Irrigation Process", Germany.
[5] Google Earth, 2015.
[6] Pavlic, M. U., and Praznik, B. L. A. Z. (2001). Detecting
karstic zones during highway construction using
ground-penetrating. Acta Geotechnica Slovenica, 8(1),
17-27.

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