• Geophysics and Geophysical Exploration
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• v.8 no.3
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• pp.224-231
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• 2005

In geophysical field surveys, commercial equipments often fail to resolve the subsurface target or even sometimes fail to be applied because they do not fit to the various field situations or the physical properties of the medium or target. We developed a geophysical measurement system, which can be easily adapted for the various field situations and targets. The system based on PXI with A/D converter and some stand alone equipment such as Network Analyzer was applied to borehole radar survey, borehole sonic measurement and electromagnetic noise measurement. The system for borehole radar survey consists of PXI, Network Analyzer, dipole antennas, GPIB interface is used for PXI to control Network Analyzer. The system for borehole sonic measurement consists of PXI, 24 Bit A/D converter, high voltage pulse generator, transmitting and receiving piezoelectric sensors. The electromagnetic noise measurement system consists of PXI, 24 Bit A/D converter, 2 horizontal component electric field sensors and 2 horizontal and 1 vertical component magnetic filed sensors. The borehole radar system has been successfully applied to detect the width of the artificial tunnel through which the borehole pass and to image buried steel pipe, while the commercial borehole radar equipment failed. The borehole sonic system was tested to detect the width of artificial tunnel and showed a reasonable result. The characteristic of electromagnetic noise was grasped at an urban area with the data from the electromagnetic noise measurement system. The system is also applied to characterize the signal distortion by induction between the electric cables in resistivity survey. The system can be applied various geophysical problems with a simple modification of the system and sensors.

• Economic and Environmental Geology
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• v.35 no.6
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• pp.567-573
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• 2002

Two-dimensional MT (Magneto-Telluric) modeling is performed to verify the validity of difference arrow for GDS(Geomagnetic Depth Sounding) survey. The electromagnetic mutual coupling between the sea and in-land conductor is used as a criterion that judges the validity of difference arrow. In this study, the mutual coupling between them is examined according to the spatial distance between them and the period of magnetic variations. The difference arrow is valid for conductors located at surface which are far from the sea or when the long period is used, but the mutual coupling is weak for buried conductor in all the periods. However, when a conductor extends vertically down to the deep part, the validity of difference arrow is in doubt, since the strong mutual coupling influences up to the long period. Therefore, to remove the known conductor effect such as sea effect from the observed induction arrow, the mutual coupling between them must be examined and the caution must be exercised in interpreting the resultant difference arrow if mutual coupling between them is strong.