• Journal of the Korean Geosynthetics Society
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• v.13 no.1
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• pp.23-31
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• 2014

In this study, the method to measure effectively the ground surface displacement of slope was proposed using the Laser Distance Measurer (LDM). Applying the proposed technique is more simple and easier than the complicated and high-priced instrument to measure the ground surface displacement. LDM is an instrument that the red laser aimed at the target and then the reflected laser used for calculating the distance. The advantages of LDM are easy operating method, high measurement precision and lower in price. To check the feasibility, the proposed method applied to the real site that the ground surface displacement of slope was occurred continuously. The ground surface displacements were occurred in various points of the natural and cut slopes located at the lower part of coal mine waste heap due to the load of waste heap. To measure directly the ground surface displacement in this site, 6 measurement sections and 26 measurement points were selected. As the result of the displacement measured by the proposed technique within a certain period time, the accumulative ground surface displacement could be measured as well as the velocity of displacement could be estimated. Also, the progress direction of ground surface displacement can be confirmed and predicted through the analysis of all measured result.

• Journal of the Korean GEO-environmental Society
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• v.22 no.7
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• pp.13-20
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• 2021

The problem of subsidence of the roadbed near the Honam High Speed Railway, which opened in April 2015, continues to be raised, and the ground stability of the area near the Honam High Speed Railway may also be problematic. It is very important to select the factors that determine the indicators and indicators in producing the risk maps. Existing risk indicators are calculated as the final displacement volume based on the last observed date of the observed period, and time-series indicator displacement must be identified to analyze the cause of subsidence and the behavior of the indicator. Furthermore, for a wide range of regions, it is economically inefficient to conduct direct level measurements, so we wanted to observe surface displacement using SAR images. In this paper, time series indicator displacement was observed using PS-InSAR techniques, and risk was compared by rating each factor using the difference between final indicator displacement, cumulative indicator displacement, minimum displacement and maximum displacement as factors for determining risk indicators. As a result, the risk rating of the final displacement is different from that of each factor, and we propose adding factors from different perspectives in determining risk indicators. It is expected to be an important study in finding the cause of ground subsidence and finding solutions.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2017.11a
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• pp.369-371
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• 2017

지반침하는 열차 탈선과 같은 대형재난을 야기할 수 있다. 그러므로 지반침하를 사전에 파악하기 위한 다양한 연구가 진행 중이다. 최근 광범위한 지역의 지표변위를 경제적으로 분석할 수 있는 InSAR(nterferometric SAR)기법을 이용한 연구가 활발히 진행되고 있다. InSAR 기법 중 PS-InSAR(Permanent Scatterer Interferometric SAR)기법이란 SAR영상에서 긴밀도가 높은 고정산란체(PS:Permanent scatterer)를 이용하여 지반침하를 분석하는 기법으로 다른 InSAR 기법에 비해 대기에 의해 발생하는 오차가 적으며, 보다 정확한 지표변위량을 도출할 수 있다. 또한 장기간에 걸친 시계열적 지표 변위 분석에 용이하다. 본 논문에서는 독일의 Terra SAR-X 위성 영상을 이용하여, 광주광산구의 지표변위를 분석하였다. 연구지역인 광주 광산구는 대표적인 연약지반인 평야지역에 위치해 있으며, 실제로 2015년 한국시설안전공단의 발표에 의하면 6곳의 지반탐사 필요 의심지역이 존재할 만큼 지반이 불안정한 지역이다. 연구 결과 광주 광산구 8mm/year로 지반이 침하되고 있음을 알 수 있었다. 이에 광주 광산구 일대의 지반침하 대비를 위해 다양한 노력들이 필요할 것으로 사료된다.

• Korean Journal of Remote Sensing
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• v.24 no.2
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• pp.165-177
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• 2008

Small baseline subset (SBAS) algorithm has been recently developed using an appropriate combination of differential interferograms, which are characterized by a small baseline in order to minimize the spatial decorrelation. This algorithm uses the singular value decomposition (SVD) to measure the time-series surface deformation from the differential interferograms which are not temporally connected. And it mitigates the atmospheric effect in the time-series surface deformation by using spatially low-pass and temporally high-pass filter. Nevertheless, it is not easy to correct the phase unwrapping error of each interferogram and to mitigate the time-varying noise component of the surface deformation from this algorithm due to the assumption of the linear surface deformation in the beginning of the observation. In this paper, we present an improved SBAS technique to complement these problems. Our improved SBAS algorithm uses an iterative approach to minimize the phase unwrapping error of each differential interferogram. This algorithm also uses finite difference method to suppress the time-varying noise component of the surface deformation. We tested our improved SBAS algorithm and evaluated its performance using 26 images of ERS-1/2 data and 21 images of RADARSAT-1 fine beam (F5) data at each different locations. Maximum deformation amount of 40cm in the radar line of sight (LOS) was estimated from ERS-l/2 datasets during about 13 years, whereas 3 cm deformation was estimated from RADARSAT-1 ones during about two years.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2016.11a
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• pp.357-358
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• 2016

최근 재난에 대한 광역적 탐지 및 피해상황을 예측하는데 위성레이더 영상의 활용방안이 대두되고 있다. 본 논문에서는 SENTINEL-1 위성레이더 영상을 활용하여 지진발생으로 인한 지표변위를 관측하고자 하였다. 차분간섭기법(DinSAR)을 적용하여 최근 발생한 이탈리아 중부 지진과 한반도 경주 지진의 지표변위를 관측하고 피해범위를 예측하였다. 연구결과 규모 6.4 이탈리아 지진에서 최대 20.1cm의 침하를 관측하였으며, 규모 5.8 경주 지진의 경우 발생지역 20km 범위에서 약 3cm의 지표변위를 관측하였다. 향후 지상 SAR 자료를 구축할 예정이며 재난지역의 다각적 관측자료 취득 및 보다 정확한 재난 피해를 파악 할 수 있을 것으로 기대한다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.512-515
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• 2011

터널 해석은 주로 지표침하와 터널 라이닝 내 단면력 산정에 초점이 맞춰지며 이는 시공단계를 고려한 3차원 수치해석 모델을 이용해 결정할 수 있다. 수치해석 시 shield는 응력 제어, shell element로 모델링하는 방법 등으로 모사될 수 있다. 한편 변위 제어를 통한 쉴드 모사는 shield를 적절한 경계조건으로 처리함으로서, 다른 shield 모사 방법에 비해 모델링 작업을 간소화하고 해석의 효율성을 높일 수 있다. 본 연구에서는 변위 제어에 의한 shield 모사를 위한 적정 경계조건을 제안한다. 이를 위해 시공단계가 고려된 유한요소해석을 사용하여, 쉴드 및 굴착면에서의 경계조건 변화와 이에 따른 지표침하 관측 수행하였다. 제안된 shield 변위 제어로부터 얻어진 해석결과를 이론적인 해와 비교함으로서, 제시된 shield 모델링 방법의 적정성과 지반 거동 변화를 평가하고자 한다. 해석 결과는 지반 모델의 지표침하를 기준으로 관찰되었으며, 변위제어에 의한 결과와 요소에 의한 모델링 결과가 유사하게 얻어짐을 보여준다. 또한 변위제어의 쉴드 모사에서 회전 구속보다 변위 구속 조건에 지배적으로 영향을 받음을 확인하였다.

• Korean Journal of Remote Sensing
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• v.34 no.6_4
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• pp.1489-1501
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• 2018

In 2016 Kumamoto, Japan, the foreshocks of $M_j$ 6.5 and 6.4, mainshock of $M_j$ 7.3 besides more than 2,000 aftershocks occurred in succession. Large surface deformation occurred due to this serial earthquakes and three-dimensional measurements of the deformation have been presented for the study of fault structures (Baek, 2017). The 3d measurements retrieved from two ascending pairs (20160211_20160602, 20151119_20160616) and a descending pair (20160307_20160418) acquired from ALOS PALSAR-2. In order to avoid mixing ionospheric error components on along-track surface deformation, the descending multiple-aperture interferogram, which do not contain the deformation of aftershocks after 20160418, was utilized. For these reason, there was a temporal discrepancy of about 2 months in extracting the north-south deformation. In this study, we applied a directional filter based ionospheric correction to ascending multiple-aperture interferograms, in order to reduce this discrepancy and understand more accurate fault movements. As a result of the ionospheric correction, an additional displacement signal was observed nearby fault lines. The root-mean-squared errors compared to GPS were about 9.87, 8.13 cm respectively. These results show improvements of 4.8 and 6.4 times after ionospheric correction. We expected that these along-track measurements would be used to decide more accurate movements of faults related to the 2016 Kumamoto Earthquake.

• Korean Journal of Remote Sensing
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• v.29 no.1
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• pp.21-34
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• 2013

Permanent Scatterer InSAR (PSInSAR) technique extracts permanent scatterers exhibiting high phase stability over the entire observation period and calculates precise time-series deformation at Permanent Scatterer (PS) points by using single master interferograms. This technique is not a good method to apply on nature environment such as forest area where permanent scatterers cannot be identified. Another muti-temporal Interferometric Synthetic Aperture Radar (InSAR), Small BAseline Subset (SBAS) technique using multi master interferograms with short baselines, can be effective to detect deformation in forest area. However, because of the error induced from phase unwrapping, the technique sometimes fails to estimate correct deformation from a stack of interferograms. To overcome those problems, we introduced new multi-temporal InSAR technique, called Temporarily Coherence Point InSAR (TCPInSAR), in this paper. This technique utilizes multi master interferograms with short baseline and without phase unwrapping. To compare with traditional multi-temporal InSAR techniques, we retrieved spatially changing deformation because PSs have been found enough in forest area with TCPInSAR technique and time-series deformation without phase unwrapping error. For this study, we acquired ERS-1 and ERS-2 SAR dataset on Augustine volcano, Alaska and detected deformation in study area for the period 1992-2005 with SBAS and TCPInSAR techniques.

• The Journal of Engineering Geology
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• v.33 no.2
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• pp.275-291
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• 2023

Global warming has made the polar regions more accessible, leading to increased demand for the construction of new resource-development plants in oil-rich permafrost regions. The selection of locations of resource-development plants in permafrost regions should consider the surface displacement resulting from thawing and freezing of the active layer of permafrost. However, few studies have considered surface displacement in the selection of optimal locations of resource-development plants in permafrost region. In this study, Analytic Hierarchy Process (AHP) analysis using a range of geospatial information variables was performed to select optimal locations for the construction of oil-sands development plants in the permafrost region of southern Athabasca, Alberta, Canada, including consideration of surface displacement. The surface displacement velocity was estimated by applying the Small BAseline Subset Interferometric Synthetic Aperture Radar technique to time-series Advanced Land Observing Satellite Phased Array L-band Synthetic Aperture Radar images acquired from February 2007 to March 2011. ERA5 reanalysis data were used to generate geospatial data for air temperature, surface temperature, and soil temperature averaged for the period 2000~2010. Geospatial data for roads and railways provided by Statistics Canada and land cover maps distributed by the North American Commission for Environmental Cooperation were also used in the AHP analysis. The suitability of sites analyzed using land cover, surface displacement, and road accessibility as the three most important geospatial factors was validated using the locations of oil-sand plants built since 2010. The sensitivity of surface displacement to the determination of location suitability was found to be very high. We confirm that surface displacement should be considered in the selection of optimal locations for the construction of new resource-development plants in permafrost regions.

• Proceedings of the KSRS Conference
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• 2008.03a
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• pp.148-152
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• 2008

뉴올리언스는 미시시피 강 하구에 위치하였으며 지난 2005년 허리케인 카트리나에 의해 큰 침수 피해를 입은 지역이다. 이 도시는 신생대 지층에 자리하고 있어 미고결층의 다짐작용 및 단층작용으로 최대 29mm 정도의 연간 침하율을 보여 왔다. 뉴올리언스의 계속된 침하작용은 평균해수면보다 낮은 지역에 위치한 도시의 침수위험성을 가중시키고 있어 현재 이에 관한 많은 연구가 진행되고 있다. SAR영상을 이용한 차분간섭기법(DInSAR, Differential Interferometry of SAR)은 지반침하, 지진, 화산활동 등과 같이 수십 km$^2$에 걸쳐 발생하는 지표변위를 수cm-수mm의 정밀도로 관측 가능한 기술이다. 이 연구에서는 차분간섭기법을 이용하여 2005년 2월부터 2007년 2월까지 촬영된 21개의 RADARSAT-1 Fine beam mode(F5) 영상으로부터 25개의 차분간섭영상(DInSAR Interferogram)을 생성하였다. 또한 차분간섭도의 spatial decorrelation을 극복하고 시간에 따른 LOS 방향의 변위를 관측하기 위해 분석 알고리즘으로는 보완된 SBAS(small baseline subset)기법을 이용하였으며, 이 기법을 이용하여 대기의 영향 및 노이즈를 제거한 결과를 얻을 수 있었다. 우리는 LOS방향의 2차원 변위분포 맵을 작성하였으며, 그 결과 전체적인 침하율은 크지 않지만, 도시의 서쪽지점에서 나타나는 상대적으로 큰 -1.49cm/yr의 변위 값과 동쪽 지점에서 0.33cm/yr의 변위 값을 관측하였다. 이 같은 결과는 앞으로의 연구에서 실측 데이터 및 동일기간의 다른 SAR영상자료의 연구를 통해 보완해 나갈 것이다.