Archaeological Evidences Detection by using GPR Method: SB2K Site

Archaeological Evidences Detection by
using GPR Method: SB2K Site
Shyeh S.K.
Research Assistance
Centre for Global Archaeological Research, Universiti Sains Malaysia
e-mail: [email protected]
M.M. Nordiana
Lecturer
School of Physics, Universiti Sains Malaysia
e-mail: [email protected]
Shamsul Anuar
Research Assistance
Centre for Global Archaeological Research, Universiti Sains Malaysia
e-mail: [email protected]
Rosli Saad
Senior Lecturer
School of Physics, Universiti Sains Malaysia
e-mail: [email protected]
Mokhtar Saidin
Director, Senior Lecturer
Centre for Global Archaeological Research, Universiti Sains Malaysia
e-mail: [email protected]
ABSTRACT
Sungai Batu Archaeological Complex has a lot of buried artefact and monument, identified at least
have 97 potential site for excavation. The discoveries can be classified as jetty, ritual area, iron
smelting and administration site. New project named Sungai Batu Archaeological Gallery for
development and management arise on the archaeological site which will destroy in-situ archaeological
evidence, if it is there. By using non-destructive method called ground penetrating radar (GPR) is to
detect and relocate potential archaeological evidence before it’s too late. GPR Mala Geoscience
equipment with 500 MHz shielded antenna was used to detect at least at 1.5 m depth penetration.
Generally, a lot of potential anomalies keep showing up at certain spot and possibly it was iron
smelting and administrative site remains. By that, excavation will be take-over to move out all
archaeological evidence before new building will be placed at pointed location in limited time period.
This paper will focusing on SB2K site from geophysical and archaeological study.
KEYWORDS:
Sungai Batu; GPR; SB2K.
INTRODUCTION
Discoveries of Sungai Batu Archaeological Complex was started on February 2009 by
Zuraina Majid, Mokhtar Saidin and the group; surface finding in the palm oil tree detect a number
of mound (looks like small hill or heap land). Identification process was made to counting the
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number of potential site: 97 potential site was identified for excavation only on 0.5 km2 land area.
Early excavation revealed 22 site from year 2009 until 2012 with different type of monument
shape named SB1 (for northern side) and SB2 (for southern side) separated by the main road
Merbok – Semeling. Classification based on man-made structure type are jetty, ritual area, iron
smelting and administrative site. Sungai Batu Archaeological Complex located 10.5 km from
Gunung Jerai as main landmark local area, 11.5 km from Sungai Petani and 65.7 km from Alor
Setar.
Sungai Batu Archaeological Gallery was main idea, planned by PPAG and National Heritage
Department (Jabatan Warisan Negara, JWN); build as centre for development and management
activities for Sungai Batu archaeological discoveries. It will give job opportunities for local
people to directly involve manage the archaeological remains. The modern structure will be built
between SB2A and SB2F site and 10 m from main road. Building progress will start on
September 2013 and excavation stage will be start immediately for rescuing archaeological
remains.
OBJECTIVE
The main objective for this study is to detect and relocate the location of potential buried
archaeological evidence. Study area was located at SB2K, covered area 12 x 11 m2
approximately. Ground penetrating radar is the main choice as it ability to produce good data on
site and non-destructive method. Target depth of archaeological evidence layer are less than 1.5
m from top layer.
GPR offer a high resolution sounding capability with detection of features of a few tens of
millimetres thickness at ranges of several metres. The range decreases to a few metres in
conductive materials such as clays, silts and soils with saline or contaminated pore water (Davis
J.L. & Annan A.P., 1989).
GEOLOGICAL AREA
Sungai Batu Archaeological Complex located in Mahang Formation or Sungai Petani
Formation composed of argillite rock with dark grey to black colour, the rock often are
metamorphic and siliceous (Bradford, 1972). In the argillite unit consists of a thin layer of arenite
and chert rock. Shale and chert mostly in black colour contain of carbon component and rich
ferum oxide, there are also pyrite crystals interpreted as accumulate in the marine environment.
Mineral and Geoscience Department (Jabatan Mineral dan Geosains, JMG) Ipoh was invited
to made borehole study, 11 borehole records has been made at specific location. Generally,
geological area was describe as Figure 1. It show Sungai Batu contain of 4 different layers;
alluvial sediment, residual soil layer and completely weathered sediment rock or highly
weathering. Alluvial sediment consists of top soil (sandy clay and silty clay; depth 0 – 0.5 m) and
sediment layer (clay and a little of side mineral (muscovite) 0.5 – 4.5 m). Residual soil layer
contain of silty clay and presence of laterite (chunks) and quartz (gravel) (4.5 – 17.0 m).
Completely weathered sedimentary rock or highly weathering contain of weathering clay and
silty rock and a few minor element such quartz veins (17.0 – 18.5 m) coming from Mahang
Formation.
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Figure 1: General stratigraphic for Sungai Batu area (2010, after JMG Technical Report)
GROUND PENETRATING RADAR
Theory
Radar signals are transmitted into the ground and then reflected by discontinuities in the
electric properties of soil. The reflection times of the signals provide depth information ( (Moffat
D.L., 1974); (Morey R.M., 1974); (Ulriksen C.P.F., 1982); (Bevan B., 1983); (Vaughan C.J.,
1986); Finzi & Piro, 1991, 2000; Brizzolari et al. 1992d; Malagodi et al. 1996; Conyers and
Goodman, 1997; Goodman & Nishimura, 1993; Nishimura and Goodman, 2000; Goodman et al.
2004a,b, 2007; Neubauer et al. 2002; Piro et al. 2001c, 2003).
The attenuation decrease as the frequency decreases in wet geological materials. The
resolution is increased as the bandwidth is increased and this usually requires that the centre
frequency of the radar be increased (Davis J.L. & Annan A.P., 1989).
The principal weakness of GPR is that it cannot normally penetrate below a clayey horizon.
Often, the use of incorrect antenna means that important features are obscured or missed entirely.
This happens because of poor resolution of or excessive signal attenuation by the feature of
interest. Efforts are now being made to convert move out correction and signal processing seismic
techniques to radar data.
Another important attribute of radar is the resolving power, or the ability to locate small
objects. The wavelength affects the ability of the georadar to identify thin layers or isolated
features. Resolution is more than 1/2 and the depth of horizontal interfaces can be determined to
about 1/10 (Weymouth J.W., 1986). In order to get a better resolution, a higher frequency antenna
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could be used, but this would increase attenuation, while low frequency antennas have a coarser
resolution but their penetration depth is remarkably better.
Metals have essentially an infinite dielectric coefficient and thus produce very strong
reflections. A pit with a well-defined boundary will produce a better reflection. Walls and
foundations are also good reflectors. Typical archaeological applications are the search for
graves, buildings and the identification of anthropic soil transformations.
Data Acquisition
In different area of the Sungai Batu archaeological site, a previous GPR survey, surveyed on
2009, allowed to single out an anomaly likely referable to an ancient structure (Sarmiza M.S.,
Rosli Saad, Shyeh S.K., Nawawi M.N.M. and Mokhtar Saidin, 2010). Now a day, study area was
focusing on southern part area, refer as Map 1 in the orange box, to investigate the subsurface
layer. The survey run at 11st May 2013.
Map 1: Location of study area SB2K for geophysical and
archaeological site in yellow box
In order to obtain a regular grid over investigated area, a series of 11 lines, 12 m for
maximum length and 4 m for minimum length profiles with trace interval 0.01 m, were made. All
the survey lines were oriented north-south were cross on possible potential archaeological site,
Figure 2.
The radar traces were collected within a 0-28 ns time window, and in true amplitude mode,
i.e. without including any kind of filtering and/or gain. The velocity of 92 m/ns for the
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electromagnetic waves in the selected ground was obtained from previous investigations. Taking
into account the geoenvironmental conditions of the investigated area and the results of the GPR
antenna operating at 500 MHz from Mala Geoscience equipment.
ARCHAEOLOGICAL STUDY
Archaeological site was decided based on surface finding evidence, found small quantity of
brick chunks and iron slugs. Before excavation take a part, geophysical survey was done using
GPR method to give conformation. Gridding system assign 1 m x 1 m and location of excavation
trench determine from GPR result.
The survey started from 15th May until 26th June 2013 compose 16 holes of trench has been
made named as C5, E8, E9, F2, F5, F7, F8, F9, F12, G7, G8, G9, G12, H8, H9 dan J5, refer to
Figure 2. Coordinate of location pin point of the centre of the study area, N05° 41’ 40.18” and
E100° 27’ 16.11” with altitude estimated 10 m from sea level.
Figure 2: Location of study area SB2K, route of GPR survey and archaeological
excavation trench. Orange box indicates the location of 3D GPR processing data
Every archaeological finding will be recorded based on trench name, 4 different type of
quadrants, 3D measurement based on depth and nearest wall trench. Discoveries such char coal,
bones and soil sample can be used to determine and estimate the true or relative age of culture
layer.
After archaeological sample has been taken out from trench, the sample will be clean out
before analysis process can be done. Some analysis take time to get the result such radiocarbon
technique.
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8574
RESULT AND DISCUSSION
Archaeological Data
Seven different types of findings have been identified such shells, pottery, bones, tuyure, iron
slags, ceramics and beads, refer to Figure 3. Most of the trench has been discover the iron slags
with different kind of quantity. Tuyure was discover at C5, E8, E9, F7, F8, F9, G7, G8 and G9.
Pieces of pottery was identified not in fully shape at E8, F2, F8, G8, H8 and H9. Fresh water
shells found some in complete shape and not, located at F8, G8 and G9. Uniquely, animal’s bone
and teeth has been discover in small quantity and not in fully form, located at E9, F8, G7, H8 and
H9. Small amount of beads founded not in fully shape located at F9 and G12. Lastly, small
fragment of ceramics located at G12 only.
Figure 3: (a) Archaeological excavation and distribution findings for site SB2K (b) Some photo
of archaeological findings – animal’s teeth, bead and ceramic (top – down)
The depth of excavation was various depending on archaeological artefact findings, refer to
Table 1. Mostly bottom of culture layer at 0.9 m but slightly less for 0.3 m.
Trench
Topsoil
(cm)
C5
E8
E9
F2
30
80
70
30
Start
Culture
Layer
(spit)
4
9
8
4
Table 1: Excavation trench for SB2K
Culture
Layer
Thickness
(cm)
10
20
20
10
Below
Culture
Layer
Type
clay
clay
clay
clay
Trench
Topsoil
(cm)
F12*
G7
G8
G9
30
80
70
90
Start
Culture
Layer
(spit)
4
9
8
10
Culture
Layer
Thickness
(cm)
20
20
10
Below
Culture
Layer
Type
clay
clay
clay
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F5
F7
F8
F9
50
80
80
80
6
9
9
9
40
20
20
20
8575
clay
clay
clay
clay
G12*
H8
H9
J5*
30
80
90
50
4
9
10
6
20
20
-
clay
clay
-
*Excavation trench until culture layer
Geophysical Data
All the collected traces presented a low-frequency noise, probably caused by the groundantenna coupling, and consequently a low signal-to-noise (S/N) (Malagodi et al. 1996; Tillard,
1994). To attenuate the presence of low- and high-frequency noises and to enhance the S/N ratio,
a pass-band filter was applied.
GPR cross section of south-north survey lines has been perform, as Figure 4. From 11 lines
survey, only line L1 – L5 has been perform in 3D GPR data processing, by using Easy 3D
software. 3 lines detected has potential anomalies at L3; 7.9 – 8.6 m at depth 0.5 m, L6; 2.0 – 7.8
m at depth 0.9 m and L7; 1.4 – 7.9 m at depth 0.9 m respectively. The anomalies due to
occurrence of small object of archaeological artefact buried beneath the spotted location.
Figure 4: Seven parallel GPR cross sections for survey lines oriented in south-north direction.
Location of anomalies are marked in red circle
The study area is presented in 3D cube with top view, side view and front view, refer Figure
5. Results are cut at depth 0.4 m from top view which shows an anomalies distribution. 3D cube
cut also cut at x = 7.6 m and y = 0.4 m distance in order to show better anomalies distribution.
Potential anomalies spotted with red remark showing distribution location of possible
archaeological artefact.
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8576
(a)
(b)
(b)
(d)
Figure 5: block and sub-block views to focus on the anomaly at SB2K
(a) 3D cube of GPR data that covers area of 12 m x 5 m x 1.4 m (b) 3D cube cut at z = 1 m (c) 3D
cube cut at y = 0.4 m (d) 3D cube cut at x = 7.6 m and y = 0.4 m
CONCLUSION
GPR successfully detected a possible historical archaeological sample buried beneath the
earth but cannot identified each anomaly by specific type such as iron slags, tuyure, pottery, fresh
water shells, animal’s bones and teeth, beads and ceramics. Geophysical survey detect possible
anomalies at L3; 7.9 – 8.6 m at depth 0.5 m, L6; 2.0 – 7.8 m at depth 0.9 m and L7; 1.4 – 7.9 m at
depth 0.9 m respectively, which located almost the same distance with existing excavation trench.
3D views give clearer image of the subsurface over the survey area where the distributions of
anomalies are well mapped. The culture layer mostly detected at range of depth of 0.3 – 0.9 m.
GPR is useful in mapping the subsurface for preliminary of any structure that favourable with
archaeological perspective.
ACKNOWLEDGEMENT
Authors wish to express gratitude to CGAR USM and USM Geophysical Unit for the support
in this research. Many thanks to JWN who support the grant in this project, amount of RM
50,000.00 with duration project around 60 days.
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