New Method of Ground Penetrating Radar for Delineation and

Mapping of Shallow Coal Seam

Eddy Ibrahim

, Maulana Yusup

and Lilik Hendrajaya

Department of Mining Engineering, Faculty of Engineering, Universitas Sriwijaya, Palembang, Indonesia

Department of Physics, Faculty , Faculty of Mathematical and Natural Sciences,

Institut Teknologi Bandung, Bandung, Indonesia

Keywords: GPR Application, Newly Acquisition and Processing GPR Design, Multi Configuration Antenna,

Shallow Coal Seam

Abstract: This article presents the practical empirical analysis and applied evaluation of the impulse radar method and

shows that significant performance benefits can be achieved in ground penetrating radar applications. These

benefits are successfully demonstrated in field trials of a newly-designed acquisition and processing GPR

system. An original contribution has been made in establishing a method of the measurements of GPR for

coal seam. This enables the maximum penetration depth of a GPR system to be characterized of shallow

coal seam as basic analogue recording radar system with multi-configuration antenna. Similarly, the

resolution is expressed as basic analogue recording radar system with antenna orientation variation which is

also selective with frequency antenna. These expressions prove to be useful to design acquisition and

processing in characterizing GPR performance and could improve data quality, and then could allow

information other than reflector depth for a defined application. A design acquisition of impulse radar

technique is undertaken, which demonstrates the empirics of an impulse radar technique using multi

configuration antenna with fixed offset. It is concluded that a physically realizable newly acquisition

method of GPR has far reaching benefits in the form of higher resolution images from raw data.

1 INTRODUCTION

Under coal outcrop in general there are clay layers.

Coal layering that is not exposed at surface is

usually embosomed by clay layer, above and under

coal seam. In coal exploitation phase, information

about coal thickness, its position, fracture plane and

its water content is highly required. Such

information is required for initial determinations of

topping-off overburden, digging direction and coal

rank. Information of coal seam as well as its

overburden thicknesses can increase efficiency in

digging process because the volume of overburden

layer which must be dug can be estimated.

Currently, intensive boring must be carried out to

know the information and many boring points must

be set up to estimate lateral position of coal and

thickness of its overburden.

This boring step which must be carried out

results in a high production cost. Information about

fracture planes in coal outcrop can serve the purpose

of initial determination of digging direction. At

present in the exploitation stage of coal production,

the blade at bulldozer or bucket at bucket wheel

excavator appears to be dull quickly due to digging

orientation which is perpendicular to fracture planes

in coal seam. Besides the impact of way of the

digging, inefficiency in equipment performance is

generated since the need of fuel increases and

results in higher production cost (Ibrahim et al.,

2004 and Ibrahim, E, 2005).

To obtain the information mentioned above, it is

necessary to apply a method that must fullfill certain

criteria due to physical properties of coal that is easy

to fall into pieces and does not have pores (Van

Krevelen, 1993). Such criteria are for example: not

destructive since the nature of coal is fragile, high

resolution which is required to obtain information of

water content and fracture plane in coal, continuous

and quick in operation which is needed for overall

information in coal seam. Ground-penetrating radar

(GPR) represents one of altenative and promising

methods to overcome such problems. Moreover, the

application of GPRfor coal exploration is so far not

Ibrahim, E., Yusup, M. and Hendrajaya, L.

New Method of Ground Penetrating Radar for Delineation and Mapping of Shallow Coal Seam.

DOI: 10.5220/0009898400002480

In Proceedings of the International Conference on Natural Resources and Sustainable Development (ICNRSD 2018), pages 107-111

ISBN: 978-989-758-543-2

107

in standard form, especially in the acquisition mode

and its data processing (Annan, 2001).

This article describes an attempt to optimally

image layered coal seams by setting up a standard

design of acquisition modes of GPR and its data

processing.

2 METHODS

In order to get a reliable result to set a new

procedure in designing acquisition and its data

processing for shallow layered coal, 3 stages of

investigation were established: measurement on coal

samples at laboratory scale, 2D and 3D forward

modeling and field measurement.

2.1 Measurement at Laboratory Scale

Measurements in laboratory were carried out on coal

samples taken from coal outcrop at Tanjung Enim,

South Sumatra, Indonesia to determine their

dielectric constants at 1GHz frequency. This was

done using reflection principle with 1GHz antenna

frequency. The resulted data were then processed to

determine dielectric constant values. To obtain

reliable results, some processing steps were carried

out: spiking deconvolution, dewow, declip, set-time

zero, fk-filtering, frequency filtering and time to

depth conversion. From the processed data,

dielectric constant values were then determined.

These values of dielectric constants would be used

as input parameter for modelling of high frequency

electromagnetic waves in 2D and 3D.

2.2 2D and 3D Forward Modelling

Using dielectric constants resulting from laboratory

samples and geometry of 2D as well as 3D body, a

forward modelling was carried out. It was

implemented with free-availably GPRMax2D and

GPRMAx3D (Giannopoulos, 2003 and Ibrahim,

2005). It is based on FDTD scheme after Yee

(Yee,1966).

The result of 2 D modelling of coal body

surrounded by clay is as follows (see fig. 1).

Figure 1: Two Dimension (2D) Modeling of coal and

Clay (Ibrahim, 2005)

The position of coal could be determined,

which is based on its signature (fig. 2).

Figure 2: Radargram from the result of execution 2 D

modelling of coal and clay (figure 1) (Ibrahim, 2005)

Figs. 4 and 5 show the results of 3D modelling

as shown in fig. 3.

Figure 3: Coal modelling with fracture planes and clay

layer under coal (Ibrahim, 2005)

Figure 4. Radargram for x direction polarization (xx

mode) from the result of execution coal modelling with

fracture planes and clay layer under coal (figure 3)

(Ibrahim, 2005)

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108

Figure 5: Radargram for y direction polarization (yy

mode) from the result of execution coal modelling with

fracture planes and clay layer under coal (figure 3)

(Ibrahim, 2005)

It can be seen that fracture planes could be

determined, in which xx configuration gave more

clearer radargram compared with that of yy

configuration.

2.3 Measurement of Limited Field

Scale

Measurement on coal outcrop (fig. 6) was conducted

at Bukit Asam mine shaft, Tanjung Enim, South

Sumatra with various antenna orientation (fig. 7).

Figure 6: Measured coal outcrop (Ibrahim, 2005)

Figure 7: Acquisition mode of reflection profiling using

bistatic antenna with centre frequency of 100 MHz direct

on coal outcrop (Ibrahim, 2005)

GPR campaign with 100 MHz was assigned.

Three different antenna orientations (yy, xx and yx

configurations) were used. The height of the antenna

for 3 different configurations were the same, in that

the antenna stood direct on outcrop. (Ibrahim et.al,

2004)

The acquired data were then processed with

processing steps similar to the steps applied on

radargram from measurement in laboratory. In

addition, influences of water content and fracture

planes detected by each variation of antenna

orientation (yy, xx and zx configurations) are also

shown in the results.

For verification of the results of acquisition and

processing steps that we propose here, we also

applied them for the data taken from coal outcrop

with same coal rank but different physical properties

laterally.

3 RESULTS

A forward modelling of 2D or 3D body with

dielectric constant for coal with various ranks as

input data results radargram is shown in figs.2, 4 and

5. In general, 2D modelling provided information of

clear coal position, which was based on signature in

the form of waveform. To define the existence of

fracture planes, 3D modelling should be applied. In

some cases numerically, multiple effects always

existed in data since the value contrast of dielectric

constant between coal and clay was very large.

Practically such an effect was also recognizable in

raw data. Determination of dielectric constant of

coal samples was carried out by using GPR antenna

with 1 GHz frequency. Similar processing steps to

data acquired from field measurement were applied

to data from laboratory measurement.

Measurement with yy configuration could

produce information of thickness of coal seam and

various water content in coal seam. (fig. 8).

Figure 8: Profile of acquired GPR records after processing

at coal outcrop in yy mode (Ibrahim, 2005)

New Method of Ground Penetrating Radar for Delineation and Mapping of Shallow Coal Seam

109

Measurement with xx configuration provided

information of the existence of fracture planes and

water content variation in coal seam as well as its

thickness.(fig. 9)

Figure 9: Profile of acquired GPR records after processing

at coal outcrop in xx mode Ibrahim, 2005)

Information of fracture planes and water content

could be extracted from the measurement with yx

antenna configuration, but that of the coal seam

thickness could not be clearly determined (fig. 10).

Figure 10: Profile of acquired GPR records after

processing at coal outcrop in yx mode (Ibrahim, 2005)

For implementation to real condition of field, yy

configuration showed the results of accurate

measurement of various coal positions and geometry

on various field conditions and locations with

reasonable results. Information of the thickness and

water content extracted from the measurement using

multi-configuration as applied in this investigation

could be validated with the result from direct

measurement (Ibrahim et al., 2004). In addition,

some techniques in the interpretation phase are a

valuable tool to aid in the interpretation. Windowing

attribute could be applied to determine variation in

water content laterally using various antenna

configurations (yy, xx and yx configurations) as well

as to distinguish water content from coal with 2

different ranks laterally on the basis of amplitude

values. High value of amplitude intensity is

associated with high water content and vise versa

(Ibrahim, 2005).

The thing there proved with measurement at

different positions and coal dimension at location

was different from accountable result. Information

of thickness and water content from coal outcrop by

using measurement of this way its (the result could

be validated with the result of direct measurement

analysis) (result of measurement of outcrop

geometry and result of laboratory analysis from the

sample taken at the outcrop) (Ibrahim, 2005).

Window attribute (interval of Amplitude) was

applicable to determine lateral variation of coal water

content good to antenna; configuraton variation (way

of yy, way of xx or way of yx) also to differentiate

water content of two coal ranks which are different

laterally based on values of amplitude. High

amplitude intensity value is associated with high

water content while low amplitude intensity value is

associated with low water content (Ibrahim, 2005).

4 CONCLUSIONS

It is concluded that the results from 2D and 3D

forward modelling are generally in concordance

with the results of field measurement. Such a

modelling can therefore be made as an aid tool to

design field measurement in order to achieve an

optimal result. This optimalisation is realized in the

form of determination of position and orientation of

direction of the antenna and steps of which need to

be performed regarding data processing. It includes

determination of signature coal in radargram,

elimination of direct wave and multiple reflection

and determination of the use of antenna with

appropriate selected frequency and procedure to

analyse the result of data processing. From coal

physical aspect, it needs to be recognized whether

the direction of fracture plane is approximately

parallel or perpendicular to strike. The information

can be extracted with the use of antenna

The results of field measurement data indicate

that the information of fractureplane can be

extracted using yx-configuration. Such information

can not be obtained using 2D and 3D forward

modelling that excludes changes of EM wave

polarisation after being reflected by conductive

medium in its algorithm. Then if the fracture plane

orientation is unknown, measurement of GPR at coal

outcrop must use three configurations, i.e. yy-, xx

and yx-configurations. In general, based on the

results from measurement with various antenna

orientations as well as their data processing and

analysis, it is concluded that GPR is a reliable tool in

the stage of coal exploitation.

Specifically this research gives a scientific

contribution from the use of GPR in coal

exploitation phase, which introduces a new

procedure in data acquisition and processing to

ICNRSD 2018 - International Conference on Natural Resources and Sustainable Development

110

obtain structural information, i.e. layering and

fractureplane and information of lithology (water

content and coal rank). A GPR survey for coal

exploitation should be designed using three different

antenna orientations: xx, yy and yx in the case that

fracture plane orientation is unknown. In the case

that fracture plane orientation is recognized, survey

line using xx antenna orientation is sufficient to be

carried out. The orientation of survey line is

arranged to be perpendicular to the fracture plane

orientation.

This investigation is very important in coal

exploitation since the application of GPR in coal

mining has been very limited so far. This is due to

the low dielectric contrast between the coal seam

and surrounding host rocks.

ACKNOWLEDGEMENTS

We thank PTBA (Perusahaan Tambang Batubara,

Bukit Asam) for granting permission to publish this

paper. We wish to express our gratitude Sriwijaya

University and Faculty of Engineering Sriwijaya

University for the supportive funding of this

research and sponsorship

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