• Geophysics and Geophysical Exploration
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• v.9 no.4
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• pp.279-290
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• 2006

The borehole radar methods used to tunnel detection are mainly classified into borehole radar reflection, directional antenna, crosshole scanning, and radar tomography methods. In this study, we have investigated the feasibility and limitation of each method to tunnel detection through case studies. In the borehole radar reflection data, there were much more clear diffraction signals of the upper wings than lower wings of the hyperbolas reflected from the tunnel, and their upper and lower wings were spreaded out to more than 10m higher and lower traces from the peaks of the hyperbolas. As the ratio of borehole diameter to antenna length increases, the ringing gets stronger on the data due to the increase in the impedance mismatching between antennas and water in the boreholes. It is also found that the reflection signals from the tunnel could be enhanced using the optimal offset distance between transmitter and receiver antennas. Nevertheless, the borehole radar reflection data could not provide directional information of the reflectors in the subsurface. Direction finding antenna system had a advantage to take a three dimensional location of a tunnel with only one borehole survey even though the cost is still very high and it required very high expertise. The data from crosshole scanning could be a good indicator for tunnel detection and it could give more reliable result when the borehole radar reflection survey is carried out together. The images of the subsurface also can be reconstructed using travel time tomography which could provide the physical property of the medium and would be effective for imaging the underground structure such as tunnels. Based on the results described above, we suggest a cost-effective field procedure for detection of a tunnel using borehole radar techniques; borehole radar reflection survey using dipole antenna can firstly be applied to pick up anomalous regions within the borehole, and crosshole scanning or reflection survey using directional antenna can then be applied only to the anomalous regions to detect the tunnel.

• The Bulletin of The Korean Astronomical Society
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• v.24 no.2
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• pp.79-79
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• 1999

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2006.04a
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• pp.138-138
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• 2006

• Journal of the Korean Mathematical Society
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• v.38 no.4
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• pp.711-722
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• 2001

We survey recent results on the inverse kinematic problem arising in geophysics. The question is whether one can determine the sound speed (index of refraction) of a medium by measuring the travel times of the corresponding ray paths. We emphasize the anisotrpic case.

• The Bulletin of The Korean Astronomical Society
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• v.25 no.1
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• pp.30-30
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• 2000

• 한국지구물리탐사학회:학술대회논문집
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• 2004.06a
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• pp.260-265
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• 2004

• Geophysics and Geophysical Exploration
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• v.18 no.3
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• pp.162-166
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• 2015

• Proceedings of the KSEEG Conference
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• 2001.04a
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• pp.344-345
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• 2001

• Journal of The Korean Astronomical Society
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• v.44 no.3
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• pp.97-108
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• 2011

The photometric light curves of the W-type W UMa eclipsing contact binary system BB Pegasi have been found to be extremely asymmetric over all the observed 63 years in all wavelengths UBVR. The light curves have been characterized by occultation primary minima. Hence, the morphology of these light curves has been studied in view of these different asymmetric degrees. The system shows a distinct O'Connell effect, as well as depth variation. A 22.96 years of stellar dark spots cycle has been determined for the system. Almost the same cycle (22.78 yr) has been found for the depth variation of MinI and MinII. We also present an analysis of mid-eclipse time measurements of BB Peg. The analysis indicates a period decrement of $5.62{\times}10^{-8}$ day/yr, which can be interpreted in terms of mass transfer at a rate of $-4.38{\times}10^{-8}M_{\odot}$/yr, from the more to the less massive component. The O - C diagram shows a damping sine wave covering two different cycles of 17.0 yr and 12.87 yr with amplitudes equal to 0.0071 and 0.0013 day, respectively. These unequal durations show a non-periodicity which may be explained as a result of magnetic activity cycling variations due to star spots. The obtained characteristics are consistent with similar chromospherically active stars, when applying the Applegate's (1992) mechanism.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.26 no.1
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• pp.31-41
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• 1998

The climatic characteristics of summer in 1998 are analyzed with the weather observational data and the upper air observational data. The temperature of that period is lower than that of normal years and the precipitation is larger. Due to the heavy rainfall which started at July 31, rain pured down compared to normal years and the maximum precipitation recorded at the many observational stations, particularly in Seoul, Kyunggi-Do region and mountanious districts like Taegwallyong, Mt. Sokri and Mt. Chiri. The patterns of general circulations in 1982/98 and 1997/98 are compared each other and are analyzed. The anomaly patterns of stream functions on winter in two El Nio years are simialr. The counterclockwise circulation occurred near the date line and the clockwise circulation was appeared near the Hwanam region and Alaska. These patterns are opposite to those of La Nia year, 1988/89. And the anomaly patterns of 500hPa geopotential height in summer are similar, too. The low temperature and much rain were dominated in summer of 1997/98. These phenomena is similar to the existing results of research, that temperature is low and precipitation is large in summer of El Nio years.