• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.191-194
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• 2008

The cavity behind the tunnel lining, caused by overbrake, might be cause a severe instability during tunnel construction. So backfill grouting is essentially required. GPR(Ground penetrating Radar) is widely used to identify the position and size of the cavity and to verify the effect of the backfill grouting. In this study, GPR survey with 450 MHz antenna was implied to access the effect of the backfill grouting before and after the work to the crown part of ○○ tunnel in Seoul respectively. The result of GPR survey conducted before the backfill, was revealed that cavities behind the lining were existed in the areas of 8 spans. Finally, from the GPR survey implied after backfilling, it was turned out that backfill grouting was successfully carried out. Also, GPR survey was ascertained the better contact between lining and rock base at arrangement of bar span.

• Journal of Korea Water Resources Association
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• v.53 no.6
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• pp.417-425
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• 2020

In order to predict and prevent hydrological disasters such as flood, it is necessary to accurately estimate rainfall. In this paper, an areal average rainfall estimation method using multiple elevation observation data of an electromagnetic wave rain gauge is presented. The small electromagnetic rain gauge system is a very small precipitation radar that operates at K-band with dual-polarization technology for very short distance observation. The areal average rainfall estimation method is based on the assumption that the variation in rainfall over the observation range is small because the observation distance and time are very short. The proposed method has been evaluated by comparing with ground instruments such as tipping-bucket rain gauges and a Parsivel. The evaluation results show that the methodology works fairly well for the rainfall events which are shown here.

• Geophysics and Geophysical Exploration
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• v.12 no.4
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• pp.338-346
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• 2009

Integrated analysis of GPR, impact echo (IE) and impulse response (IR) was performed to detect the rear cavity of concrete for a test-bed which was made with the same scale and component ratio to the real concrete structure. The test-bed was designed to be capable of observing various response reflecting the existence of iron reinforcing bar and cavity. GPR survey did not clearly resolve the existence of the cavity, although distinguishable responses were observed in the presence of the cavity. In contrast, IE and IR method showed distinct responses, indicating the existence of the cavity. Finally, integrated application of the three methods makes it possible to exactly identify the location of the cavity, although the iron reinforcing bar made a little variation of response.

• Journal of Environmental Science International
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• v.26 no.7
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• pp.827-836
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• 2017

Freezing rain is a phenomenon when precipitation falls as a liquid rain drop, but freezes when it comes into contact with surfaces or objects. In this study, we investigated the predictability of freezing rain and its characteristics, which are strongly related with the occurrence of black ice using synoptic scale meteorological observation data. Two different cases occurred at 2012 were analyzed and in the presented cases, freezing rain often occurs in the low-level low pressure with the warm front. The warm front due to the lower cyclone make suitable environment in which snow falling from the upper layer can change into supercooled water. The $0^{\circ}C$ temperature line to generate supercooling water is located at an altitude of 850 hPa in the vertical temperature distribution. And the ground temperature remained below zero, as is commonly known as a condition for black ice formation. It is confirmed that the formation rate of freezing rain is higher when the thickness after 1000-850 hPa is 1290-1310 m and the thickness of 850-700 hPa layer is larger than 1540 m in both cases. It can also be used to predict and estimate the generation of freezing rain by detecting and analyzing bright bands in radar observation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.12
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• pp.1036-1043
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• 2016

In this paper, an analysis about the elevation angle accuracy degradation of an APAR(Airport Precision Approach Radar) due to the multi-path effect using a phased array antenna was performed. An APAR installed around a runway of airport will be continuously affected in a runway surface of the fixed environment. In this paper, an analysis about the elevation angle accuracy degradation of APAR due to the multi-path effect of runway surface was conducted through a calculation of monopluse slope and sum/difference beam pattern analysis of array antenna. Also, a difference pattern for monopulse to minimize this degradation was optimized in an appropriate configuration to improve a elevation angle accuracy. Finally, a degree of improvement of elevation angle accuracy was confirmed by calculating a monopulse slope including the ground reflection after applying optimized difference patterns of array antenna.

• Journal of the Korean Geophysical Society
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• v.6 no.4
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• pp.261-268
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• 2003

Lots of various utilities are buried under the surface. The effective management of underground utilities is becoming the very important subject for the harmonious administration of the city. Ground Penetrating Radar(GPR) survey including other various underground survey methods, is mainly used to detect the position and depth of buried underground utilities. However, GPR is not applicable, under the circumstances of shallow depth and places, where subsurface materials are inhomogeneous and are composed of clay, salt and gravels. The aim of this study is to overcome these limitations of GPR and other underground surveys. High-frequency electromagnetic (HFEM) method is developed for the non-destructive precise deep surveying of underground utilities. The method is applied in the site where current underground surveys are useless to detect the underground big pipes, because of poor geotechnical environment. As a result, HFEM survey was very successful in detecting the buried shallow and deep underground pipes and in obtaining the geotechnical information, although other underground surveys including GPR were not applicable. Therefore this method is a promising new technique in the lots of fields, such as underground surveying and archaeology.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.7
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• pp.201-208
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• 2014

The performance of a landmine detection system depends on consistent extractions of the features of landmines. Since landmines have diverse sizes, it is critical to select an appropriate window size to represent the landmine region consistently. Conventional detection systems are incapable of extracting consistent landmine features because they employ fixed window sizes. This paper proposes a window size selection method according to the size of a landmine. The proposed method selects an appropriate window size based on the type of a landmine estimated from the response signal of the system. Data on various types of soils and landmines were generated from a simulation program to evaluate the performance of the proposed method. The results verified that the proposed method, which employs an adaptive window size, yields a better landmine detection rate than the conventional methods, which employ fixed window sizes.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.2
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• pp.83-92
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• 2018

Using ground moving target indicators equipped with synthetic aperture radars for locating moving targets within a wide background clutter in a short time is an excellent method for monitoring traffic. Although the displaced phase center antenna (DPCA) technique and along track interferometry (ATI) are real time methods with low computational complexity, they are essential for reducing cases of false alarm that can result in poor performance. In this paper, we propose two detection methods using DPCA and ATI-the parallel fusion method and serial fusion method. Simulation results demonstrate that the proposed detection methods are characterized by low probability of false alarm along with good performance. In particular, the serial fusion method possesses high detection probability along with low probability of false alarm (1/5th of the false alarm probability of the DPCA technique).

• Economic and Environmental Geology
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• v.38 no.4 s.173
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• pp.381-394
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• 2005

Mokpo city is a coastal city located at the south western coast of the Korean Peninsula. Large regions within Mokpo are subjected to significant subsidence because about $70\%$ of the city area is a reclaimed land from the sea. Although no confidential quantitative measurements are available up to the present, the subsidence rate is as much as several cm per year. In this study, we aimed to estimate the subsidence rate over Mokpo city by using twenty-six JERS-1 SAR dataset from September 1992 to October 1998. Several tens of differential interferograms were processed from JERS-1 dataset and STRM 3-arc DEM. The results indicate continuous subsidence in Dongmyung-dong, Hadang-dong and Wonsan-dong in city, and the subsidence velocity reach over 4 cm/yr in the most highly sinking area. For facilitating the analysis of time-varying surface change, we also carried out an interferometric SAR time series analysis using permanent scatterer and consequently determined space-time maps of surface deformation at each acquisition time of JERS- 1 SAR.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.209-215
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• 2017

Ground Penetrating Radar (GPR) was applied to an evaluation of the concrete condition of bridge decks with asphalt concrete. Deterioration was considered to have occurred when the relative permittivity of a concrete-faced asphalt concrete overlay showed more than 12. The relative permittivity of concrete varied considerably with the levels of porosity and water. In this study, GPR tests were carried out to determine the influence of weather and concrete condition on the relative permittivity for the research subject of an overlaid concrete bridge deck in public service. According to the test results, if bridge decks are in good condition, the relative permittivity of the top concrete of a bridge deck exhibited a normal distribution. After the deck concrete deteriorated, the relative permittivity varied with the amount of penetrated water according to the weather condition and deteriorated status of deck concrete.