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Abstract—Ground penetrating radar (GPR) is a geophysical

method that has been developed for shallow subsurface investigation and efficiently used broad area focusing in hydrogeology study. It provides non-destructive and rapid way of obtaining continuous high resolution profiles which are based on the propagation of electromagnetic waves. Conductivity and dielectric properties are two important parameters in GPR method. As in sediment, water saturation primarily causes changes in dielectric properties and therefore, this method is best applied in estimation of depth to water table. Six parallel 2-dimensional GPR lines were executed in Seri Iskandar, Tronoh, Perak, Malaysia with the aim of detecting the depth of water table and analyzing the environment of depositing sediments. Results are presented in 3-dimensional cube for better interpretation and explanation. Based on results obtained, it successfully detected the saturated zone, which suggested as water table with depth of >15-20m. Layer of reclaimed sand detected at depth <3m with nonuniform sand sedimentation and dipping layer detected at depth <10m. Wet zone is detected at depth of <10-15m.

Index Terms—Depositing sediments, electromagnetic, ground penetrating radar, water table.

I. INTRODUCTION Ground penetrating radar, (GPR) is one of the near surface

geophysical methods that involve the transmission of high frequency radar pulses from a surface antenna into the ground. It provides detailed information about the subsurface which is site-dependent and the quality of the results is dependent on the target, geologic environment, subsurface features and other factors that affect the contrast of the target to surrounding medium. It has been demonstrated that GPR is a useful sensor for shallow subsurface investigation and proven to be promising tool for subsurface characterization in the field of environmental and engineering. This is due to dielectric properties and conductivity governing GPR wave propagation are strongly correlated to basic physical properties such as water content and soil salinity. GPR method is efficiently used in a broad area focusing generally in hydrogeology study. The presence of small amount of water will dominate the behaviour of the dielectric permittivity of porous media in a multi-fluid system. The dielectric permittivity generally increases along the moisture content from the ground surface to the saturated zone [1]. In sedimentary environments, the porosity the affect the dissemination of electromagnetic waves is not equal to the total porosity but it is define as the effective porosity in which

Manuscript received August 9, 2012; revised November 19, 2012. The authors are with the Geophysics Section, School of Physics,

Universiti Sains Malaysia, 11800 USM, Penang, Malaysia (e-mail: [email protected]; [email protected]; [email protected]; [email protected])

the fluid flows freely [2]. GPR survey was performed in Seri Iskandar, Tronoh, Perak using 100MHz shielded antenna to identify depth of water table and stratigraphy of sediments deposition. Tronoh was a small tin mining town located about 30km south of Perak capital city, Ipoh, Malaysia. There are lots of manmade lakes found which are believed to occur due to tin mining industry since 20th century.

II. METHODOLOGY

A. Basic Principle Ground penetrating radar is a method that is commonly

used for environmental, engineering, hydrogeological, and other shallow subsurface investigations [3]. It has been used for several years as a non-destructive method for locating subsurface anomalies. It uses the principle of scattering electromagnetic wave (EM) to locate target or interfaces buried within visually opaque substances or earth material [4]. An electromagnetic wave is transmitted into the ground and reflected based on different dielectric properties of subsurface materials (Fig. 1). Reflected waves are received at the surface according to a general principle; the higher the frequency, the better the resolution and the shallower the depth of penetration [5].

Fig. 1. EM wave propagation depends on dielectric and conductivity

properties of material [6].

The recorded signal is registered as amplitude and polarity versus two way travel time. The electromagnetic wave propagates in air with the speed of light, 0.3 m/ns. Generally, in other medium such as ground, velocity of EM wave is reduced due to relative dielectric permittivity (εr), magnetic permeability (µr), and electrical conductivity (σ). Velocity of electromagnetic wave in a host material is given by (1)

A Study of Water Table and Subsurface Using 3-Dimensional Ground Penetrating Radar

Ismail N. Azwin, S. Rosli, Muztaza M. Nordiana, and A. H. A. Teh Saufia, Member, IACSIT

International Journal of Environmental Science and Development, Vol. 3, No. 6, December 2012

579DOI: 10.7763/IJESD.2012.V3.289

( )2

211 ωεσμε

++

=

rr

cv (1)

where c is the EM wave velocity in vacuum (0.3m/ns), ε is define as εrε0 which refer to dielectric permittivity and dielectric permittivity in free space, ω is angular frequency, and σ/ωε is define as loss factor.

For non-magnetic (µr= 1) low-loss materials, such as clean sand and gravel, where σ/ωε ≈ 0, the velocity of EM wave is reduced to (2)

ε r

cv = (2)

Several processes lead to a reduction of electromagnetic signal strength. Among the important processes are attenuation, spherical spreading of energy, reflection or transmission losses at interfaces and scattering of energy [7].

B. Factors Affecting GPR Detectability of a subsurface feature depends on

conductivity contrast, dielectric constant and geometric relationship between antennas, where electrical properties of geological materials are primarily controlled by water content and porosity. Conductivity is the ability of a material to conduct electrical current. For a solution of water, conductivity is highly dependent on salts concentration and ions, therefore the purer the water, the lower the conductivity. The dielectric constant is defined as the capacity of a material to store a charge when an electrical field is applied relative to the same capacity. Table I shows the dielectric constant, conductivity and velocity of common geological materials and medium.

TABLE I: TYPICAL DIELECTRIC CONSTANT, CONDUCTIVITY AND VELOCITY

VALUE OF COMMON MATERIALS AND MEDIUM [8]. Medium Dielectric, εr Conductivity, σ

(mS/m) Velocity, v (m/ns)

Air 1 0 0.30 Fresh water 80 0.5 0.033 Salt water 80 3x103 0.01 Dry sand 3-5 0.01 0.15 Saturated sand 20-30 0.1-1 0.06 Limestone 4-8 0.5-2 0.12 Clay 5-40 2-1000 0.06 Granite 4-6 0.01-1 0.13 Ice 3-4 0.01 0.16

III. STUDY AREA Study area takes place at Seri Iskandar, Tronoh, Perak. It is

located almost 30km south of the Perak state capital, Ipoh, Malaysia. This area is said to be underlain by original limestone beds of the Kinta Valley, presumed to be Carboniferous [9] or possibly Permian age [10] and have been severely eroded and karstified. The clastic sequence exposed in the southern part of Kinta Valley consists of alternating beds of sandstone, shale, clay or mudstone and subordinate siltstone. Reddish-brown or diagenetic iron oxide nodules, laminae, dendrites, and fracture infill are common throughout the section. The clastic sequence in this

area is most likely equivalent to Kati Beds, as Carboniferous to Permian age [11]. The sandstone beds can be up to several meters thick and are composed of rounded, well sorted, medium to coarse size quartz grain with a small proportion of black grains of heavy minerals.

Six 2-D GPR survey lines were executed in parallel with total length of 40m for each profile and line spacing of 10m to cover an area of 2000m2. The sampling frequency used is 1106 MHz while trace interval was set as 5cm in each of the profiles. Equipment used during acquisition of the data are MALA 100MHz shielded antenna with Panasonic toughbook cf29 as the display unit. Manmade lake due to tin mining industry is found located almost 500m toward Eastern of study area (Fig. 2a and 2b).

a)

b)

Fig. 2. Ground penetrating radar. a) MALA 100 MHz shielded antenna used in the study, b) study area across the sandy soil.

IV. RESULTS Fig. 3 shows a group of radargrams representing the results

obtained from six 2-D GPR profiles. Results show three clear reflection events (yellow, red and blue lines) observed at depth <3m, <10 and >15-20m respectively at all survey lines.

Clear radar signals are observed at the upper part of the profiles which are <10m and start to show the characteristics of blur image with average thickness of 5m. Greater than this depth, the radar signals are start to attenuate resulting in lost radar signal in the GPR profiles.

With an objective of obtaining the general idea of the water table and subsurface at Kota Iskandar, a 3-D cube was created including six 2-D survey lines. The presence of the water table level can be clearly verified (Fig. 4).


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Fig. 3. Six radar images. a) L1, b) L2, c) L3, d) L4 e) L5 and f) L6.

Fig. 4. 3-D perspective of the sand stratigraphy and reflector.

At depth of 3m, it is possible to see a reflector which may corresponds to top soil (Fig.5a). At depth of <10m, there is another reflector observed, which is rather parallel to the previous but undulating. The thickness of this layer is approximately 7m with some dipping event observed (Fig.5b). There is another reflector identified at depth of >15-20m which indicated other layer that may correspond to water table (Fig.5c). Reflectors observed at the study area are shown is Fig.5d.

Fig. 5: a) First reflector at depth 3m, b) second reflector at depth <10m, c) third reflector at depth >15-20m and d) total of three reflectors observed.

The 3-D cube is cut at selected distance of x, y, and z plane

for clear vision of subsurface and reflectors, including the water table layer. Fig. 6 shows the example of this cube in x, y, and z cut.

a)

b)

c)

d)

a)

b)


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Fig. 6. Cube is cut at x, y and z direction. a) 3m depth, b) distance 25m and c)

distance 15m.

The three main views in 3-D cube are top view, front view and side view. Fig.7 shows the 3-D cube at top view = 7m, front view = 30m and side view = 30m.

Fig. 7. a) x, y and z planes and b) 3-D cube cut certain distance and depth.

V. DISCUSSIONS There is clear reflection event at depth of approximately

3m. This layer may indicate as top soil due to reclamation. As the area is surrounded by manmade lake due to mining industry, it is possible to classified that the reclaimed layer is predominantly consists of dry sand layer. Deposition of alluvium made up of medium to coarse grain sand mix with clayey sand is identified at depth <10m resulting in the thickness of this layer is approximately 7m. Clear reflection of some dipping features and non-uniform layer of sediment deposition are observed throughout this layer. A zone with high moisture content, known as wet zone is identified at depth of 10-20m that may indicate wet sand. A strong boundary reflection at depth of > 15-20m is observed which shows the indication of water table due to the signal observed to be lost as the reflection coefficient of water is 1.

Electromagnetic wave cannot pass through the saturated area where the strength of the water table radar reflector is dependent on the contrast between the electrical properties of the unsaturated and saturated medium. The variation in electromagnetic parameters from the sand layers can be produced for example by changes water saturation or organic matter content. It is possible to detect the variations as radar

detect permittivity variations and the medium conductivity, which are caused by the contrast in water content changes in porosity, variations in the grain size and the presence of organic matter all of which related to the deposition history [12]. The relative permittivity is increased between areas of non-saturated sand and saturated sand which is detectable by radar. As water is highly conductive, therefore it attenuates the signal resulting in decaying of reflection amplitude and vice versa. Hence, the presence of water saturated zones was identified based on characteristic of blur image and lost signal of radar profile.

VI. CONCLUSION Ground penetrating radar plays very important role for

recognition of stratigraphy of the area as well as mapping the water table level. Based on this study, the radar profiles obtained using 100MHz shielded antenna clearly displays the water table at depth > 15-20m. Other reflectors which seem to be caused by reclaimed sand, non-uniform sedimentation of dry sand and wet zone (wet sand) are also successfully identified at depth <3m, <10m and <10-15m respectively. Results presented in 3-D cube clearly verified different layers of sand stratigraphy and reflectors. Water table level also detected and well presented.

VII. SUGGESTIONS The results obtained from GPR method can be further used

to analyze any processes such as sediment depositional process and also useful for monitoring the ground water flow. Detailed work on ground penetrating radar by producing a conductivity contour map of the area could be a great idea through amplitude analysis which acts as supporting data to prove that low amplitude of reflected electromagnetic signal is due to attenuation of the signal by highly conductive area.

Amplitude analysis has a bright future in mapping other subsurface features such as fractures, faults and any specific buried bodies. Since different subsurface features exhibit different characteristics, therefore variation in amplitude of their reflected signals could determine the features specifically which are then correlated with 3-D ground penetrating radar results for global viewing.

ACKNOWLEDGMENT Authors wish to express gratitude to all geophysics staff of

Universiti Sains Malaysia for their assistance. Our grateful thanks also extend to postgraduate students for their contribution during geophysics field data acquisition and processing stage.

REFERENCES [1] A. S. Mundher and A. F. Nashait., “Detection of water-table by using

ground penetration radar (GPR),” Engineering and Technology Journal, vol. 29, pp. 554-566, February 2011.

[2] J. M. Reynolds, An Introduction to applied and environmental geophysics, Ed: John Wiley & Sons, pp. 796, 1997.

a)

b)

c)


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[3] R. E. Sheriff, Encyclopaedic dictionary of applied geophysics, 4th edition Geophysical References Series. 2011, Society of exploration geophysicists.

[4] J. D. Jeffrey, “Ground Penetrating Radar Fundamentals,” Department of Geological Sciences, The Ohio State University, prepared as an appendix to a report to the U.S. EPA, Region V, Nov. 25, 2000.

[5] H. M. Jol and C. S. Bristow. “GPR in sediments: advice on data collection, basic processing and interpretation, a good practice guide,” Geological society London special publication, vol. 211, pp. 9-27, 2003.

[6] J. Rittenhouse. Environmental protection agency, 2008. [7] I. Møller and F. Jørgensen, “Combined GPR and DC-resistivity

imaging in hydrogeological mapping,” in Proc. 11th International Conference on Ground Penetrating Radar, pp. 1-5, 2006.

[8] M. Beres and F.P. Haeni, “Application of ground penetrating radar methods in hydrogeologic studies,” Ground Water, vol. 29, no. 3, pp. 375-386, 1991.

[9] F. T. Ingham and E. P. Bradford, The geology and mineral resourses of the Kinta Valley, Perak, Geological Survey District Memoir 9, Federation of Malaya Geological Survey, Ipoh, 1960, pp. 433.

[10] H. Fontaine and A. Ibrahim, “Biostratigraphy of the Kinta Valley, Perak,” Geological Society of Malaysia Bulletin, vol. 38, pp. 159-172, 1995.

[11] T. W. Wong, Geology and mineral resources of the Lumut-Teluk Intan area, Perak Darul Ridzuan, Geological Survey of Malaysia Map Report 3, Geological Survey Laboratory, Ipoh, Perak, pp. 96, 1991.

[12] T. Teixeira, H. Lorenzo, A. da Costa, P. Arias. GPR radar imaging of water table, salty water and sand stratigraphy in a coastal zone in Rio de Janeiro. [Online]. Available: http://webs.uvigo.es/grupotf1/research/SB02-245%20.PDF

Ismail N. Azwin was born in Alor Star, Kedah, Malaysia, on 25th September 1987. She obtained her Bachelor of Science (BSc.) in Applied Science (Geophysics) from Universiti Sains Malaysia (USM) in August 2009. She continued her study and graduated from the same university in Master of Science, (MSc.) Geophysics in September 2011 regarding the application of geophysical methods in engineering and environmental problems. She is

currently a post-graduate student in USM persuing her PhD focusing on seismic and electromagnetic wave propagation characteristics.

She has field work experiences in engineering and environmental projects including slope stability, groundwater exploration, constructions, mineral exploration and also in archaeological research. She also became a facilitator in course conducted by Minerals and Geoscience Department Malaysia in Penang and few other geophysics-related courses conducted by Geophysics Section, USM. Her research interest is about Geophysics in engineering and environmental study and wave propagation characteristics.

Ms. Nur Azwin is a member of European Association of Geoscientists & Engineers (EAGE) and Geological Society of Malaysia (GSM). She has attended few conferences and published some refereed proceeding papers.

S. Rosli was born in Penang, Malaysia, on 28th February 1960. He obtained his Bachelor of Science (BSc.) from Universiti Sains Malaysia (USM) in 1984 and Master of Science, (MSc.) in geophysics from same university in 2004. He was awarded a PhD in 2009 from USM by producing a novel protocol regarding resistivity method. He is currently a senior lecturer in geophysics section, USM. He has served at USM since year 1985. Prior joining USM, he worked

as Tutor in Matriculation Centre USM and School of Physics, USM. He is expert in all geophysical methods such as seismic reflection and

refraction, ground penetrating radar, magnetic, gravity and electrical method including 2D and 3D resistivity, induce polarization and self-potential. He is active in geophysics-related work in Southeast Asia and conducted consultation all through Malaysia, Indonesia and Brunei. His research interest is about engineering and environmental geophysics.

Dr. Rosli is a registered member of Institute of Geology Malaysia. He has attended few conferences and published several books, refereed proceeding papers and more than 80 journals. He is awarded few short-term research grants in university and national level. He was also a reviewer for some academic journal.

Muztaza M. Nordiana was born in Johor Bahru, Malaysia, on January 25, 1986. She was graduated BSc (2008) and MSc (2010) in Applied Science (Geophysics) at Universiti Sains Malaysia (USM), Malaysia. She is currently pursuing PhD at the same university. She is also conducting and teaching undergraduate and postgraduate students in their final year and research projects.

She has experienced working in field that involves engineering and environmental projects including slope, engineering and groundwater in all Peninsular Malaysia including Sarawak, Labuan and Brunei. Her research interest is about Geophysics in mineral exploration, engineering and environmental study.

Ms. Nordiana is a member of European Association of Geoscientists & Engineers (EAGE) and Geological Society of Malaysia. She was obtained fellowship from USM. She was a recipient of the Student Travel Grant Saint Petersburg 2012 sponsor by EAGE Student Affairs. She has published several journals and refereed proceeding papers. She was also received best paper award from International Conference of Arts, Science & Technology (ICAST 2012).

A. H. A. Teh Saufia was born on January 20, 1990 in Ipoh, Perak, Malaysia. She was recently graduated from Universiti Sains Malaysia (USM), Malaysia for B.Sc.(Hons) in Applied Science (Geophysics) and currently, pursuing her study in M.Sc. in Geophysics at the same university. She plays role in assisting the undergraduates and final year students during the lab session and their projects. She has working experiences related to engineering and environmental

study. She is research assistance for Centre of Global Archaeological Research (CGAR) USM related to geophysics.


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