As one of geophysical method ground penetrating radar uses electromagnetic wave propagation to detecting the anomaly object, the strong relationship between the physical properties of geological material and their electromagnetic properties enable to identification of physical structures in the sub surface. Cavities in limestone dominated rock formation sometimes made problem when construction build above in this area, as prevention to the damage affected by cavities, before construction starting to build we have to identified the possible cave location to preparing special treatment to minimize the risk. Present of cavities give electromagnetic anomaly event and the reflection signal representing changing of electrical properties when we use ground penetrating radar. We applied attributes extraction adopted from seismic method to extracting information about cavities. We use sweetness attribute extraction to identified present of cavities in limestone dominated rock formation

1. ABSTRACT
As one of geophysical method ground penetrating radar uses
electromagnetic wave propagation to detecting the anomaly
object, the strong relationship between the physical properties of
geological material and their electromagnetic properties enable
to identification of physical structures in the sub surface. Cavities
in limestone dominated rock formation sometimes made
problem when construction build above in this area, as
prevention to the damage affected by cavities, before
construction starting to build we have to identified the possible
cave location to preparing special treatment to minimize the risk.
Present of cavities give electromagnetic anomaly event and the
reflection signal representing changing of electrical properties
when we use ground penetrating radar. We applied attributes
extraction adopted from seismic method to extracting
information about cavities. We use sweetness attribute
extraction to identified present of cavities in limestone
dominated rock formation.
Keywords : ground penetrating radar survey, cavities
Firman Syaifuddin 1, Agus Hendro 2
1.Geophysical Engineering, Institute of Technology Sepuluh Nopember, Indonesia
2.Terralog Amukti Nuswa Adi, Bandung, Indonesia
Sweetness is the implementation of two combined attributes
(Envelope and Instantaneous Frequency) and is used for the
identification of features where the overall energy signatures
change in the seismic data.
Sweetness is defined by the formula:
Sweetness = Envelope / SQRT(Inst. Frequency)
The purpose of ground penetrating radar survey program is to
provide information regarding the shallow stratigraphy and to
highlight the presence of any adverse subsurface conditions
associated with possible cavities and weak strata.
The objective of the ground penetrating radar survey is to
observe subsurface condition in the available land (geocycle
platform area) concerning the occurrence of caves in
investigation area before land preparation started.
Ground penetrating radar is one of the newer geophysical
methods. By exploiting the wave propagation characteristics of
electromagnetic fields, GPR provides a very high resolution sub-
surface mapping method. In many respects GPR is the
electromagnetic counterpart of seismic reflection.
In the exploration context, GPR has limited exploration depths,
so it is not necessarily a tool for all applications. GPR is most
effective in electrically resistive environments where very
detailed information is desired.
GPR data acquisition were acquired using Mala ProEx GPR
recording unit with 25 MHz antennas using common offset
technique. Special rough terrain antennas (RTA) recently
developed by Mala were used. Specific to these antennas with
respect to normal unshielded antennas which should be oriented
perpendicular to the profile direction and are rigid, is that RTA
are flexible, in-line oriented, all-in-one antennas (Mala 2010).
The flexible “snake” like design in form of a long tube allows the
antenna to be maneuvered easily and efficiently through the
dense vegetation or uneven terrain without affecting ground
contact, providing optimum results also in difficult
environment.)

2. The guide for identification of
occurrence of cavities in limestone
environment refer to the fact that
between the karst cavities with the low
velocity within the dense limestone
with high-velocity may generate strong
reflection.
In this study we applied the sweetness
to detect occurrences of cavities.
In general, karst cavities in limestone
environment mainly occur below or
near the erosion surface and an
interference phenomenon may occur
between strong reflection of the
erosion surface and the reflection of
the cavity formation.
To asses the capabilities of
low frequency GPR and to
investigate the possible
existence of unknown cave
galleries, we planned 24
profiles oriented in N–S
direction and 18 profiles
in W-E direction.
Acquisition parameters
are summarized in Table
below. Sampling interval
was 1 ns and the
acquisition window length
1024 ns. The surface soil
layer and limestone
beneath were therefore
relatively dry.
High sweetness marked by magenta to pink color and the low sweetness
value marked by blue color. Range relative value of sweetness is 0 up to
1. The phenomenon of cavities in carbonate (limestone) environment
occur with the strong reflection (high contrast impendence) give higher
envelope amplitude and low frequency.
The sweetness sections were also used to display the energy distribution of
the traces as shown in the figures of all the profiles. The phenomenon of
cavities in carbonate (limestone) environment occur with the strong
reflection (high contrast impendence) give higher envelope amplitude and
low frequency. Fluid filled in limestone makes absorbed high frequency
component of radar data. On other word phenomenon of occurrence
cavities will be have high sweetness value.
Ground-penetrating radar was successfully utilized to map the
occurrence of cavities or fissure at this Platform area. Digital
processing and modeling of georadar data enhanced the
interpretation of cavities and provided detailed information of
position and distribution of cavity at the project site. 43 of
cavities with various dimension and depth have been identified
and geometry of caves can be presented on 2D map