Ground Penetrating Radar(GPR) is an electromagnetic (EM)geophysical method for high resolution detection, imaging and mapping of subsurface soils and rock conditions. The idea of using the propagation of high frequency EM wave for subsurface can be traced back to beginning of the century. In the addition to its numerous military and civil applications, radar is now very important tool in ground investigation, normally from the near surface to depth of several tens of meters.During more than two decades of development, GPR system have became the geophysical tools that provide the subsurface window for a variety of geological, engineering, environmental and archeological applications.
figure 1 flow chart for a typical GPR system(after Davis et al., 1989)
The most common operation mode of GPR is the reflection mode, whereby traces of returned waves are collected either continously or in stations along a line, thus creating a time cross section or profile image of the subsurface.
figure 2 GPR data acquisition use antenna 200MHz and 400MHz
GPR data are displayed on printer paper or on a computer screen during acquisition(i.e., during real time). For a given transect the data consist of a cross-section of signal amplitudes(intenities) versus location(along the two-way time axis and the horizontal axis).
Before survey in the field commenced, antenna calibrations were carried out at "place calibration". The purpose of calibration is to get the best parameters base on local gelogical setting and condition.
figure 3 Magnetic/metal good anomaly(calibration at field) use antenna 400MHz. depth metal cylinder 30cm and diameter 5cm, high 15 cm.
figure 4 Calibration magnetic/metal model for antenna 400MHz and 200MHz(Cal1)
figure 5 Acquisition and Result of model(Cal1)
figure 6 Result of magnetic/metal good anomaly(Cal 1) in time domain
Result of spectrum analysis is colours value for
each model characteristics, in Antam calibration the model (magnetic/metal
model) it have value 9000-11500 (colors
range in histogram) . These values will be reference of magnetic or metal model
in the field
figure 7 Result of magneti/metal good anomaly(Cal1) in frequency domain
As
usually, anomaly in the field are clear to definite if hyperbole shape of metallic/magnetic goods found as a respond.
Processing in base camp did for further analysis.
Field
processing, was doing until time domain processing. If in data section (time
domain) the hyperbole anomaly were not found, the area was declared clear. If
there is a hyperbole anomaly (on time domain data section), further analyze was
done using frequency analysis.
The
result of frequency analysis is determined with color bar, and then we compare
with data calibration and at field calibration to
get the value correlation between data in the field and its calibration.
flow of processing
figure 8 GPR data for UXO identification in frequency domain(Clear)
Spectrum
analysis or frequency analysis is frequency method to identify of value of each
rock or magnetic, compactness, etc which can be approach with value(color)
percentage of amplitude. From time domain data will be transformed to frequency
domain, with approximate anomaly on time domain we will be see the anomaly on
frequency domain value of each rocks, magnetic anomaly or others anomaly.
figure 9 GPR data for UXO identification in time domain(Clear)
figure 10 GPR data for UXO identification in time domain(Clear)
figure 11 Frequency analysis(Clear)
figure 12 Frequency analysis(Clear)
figure 13 Frequency analysis(Clear)
1 komentar:
Penentuan range nilai suatu benda atau objek bisa di tentukan lebih presisi dengan membandingkan dengan data kalibrasi di daerah tersebut.
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