Cave or Sinkhole Identification Using Ground Penetrating Radar or GPR
Ground Penetrating Radar or GPR is an electromagnetic profiling technique utilized for high resolution mapping of subsurface features.
The technique operates on the principle of transmission and reflection of short duration electromagnetic pulses from a transducer that is moved across the ground surface.
The energy radiates down through the subsurface and reflected back to the receiving antenna from subsurface electrical discontinuities. Various in the continuously recorded returning signal are sent to a control unit for processing and display.
We use MALÅ Rough Terrain Antenna (RTA) 25 Mhz series for Ground Penetrating Radar (GPR) surveying. The unique in-line, all-in-one, antenna design provides improved performance for deeper penetration. The flexible “snake” like design allows the antenna to be maneuvered easily and efficiently through the densest or most uneven of terrain without affecting ground contact, providing optimum results in the most difficult of environments. Max penetration is 30 – 70 meter.
The most common aquisition method in GPR survey is Radar Reflection Profiling, where transmitter and receiver anntena have a constant offset and moved on the line.
The line are prepared by separate topographic or advance team.
1 geophysicist, 2 Operator
2 local labour
Depending on the measurement distance and topography, 500 – 5000 meters per day.
In the cross-section image above, it can be seen that the color contrast is different which shows the different types of different mediums, such as limestone and air in the case of cave identification. Due to the significant difference in density between the 2 mediums, the GPR signal will be seen as a large amplitude on the radargram. The amplitude on the radargram is shown on a color scale from dark blue to dark red. Thus, for the interpretation of the cave boundary that is considered a target, we look at the amplitude shown by the radargram.
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