• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.3-3
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• 2023

수자원위성은 C-band 영상레이더(synthetic aperture radar, SAR)를 탑재한 중형급의 수자원 관리 및 수재해 감시 전용 위성이다. 수자원위성은 물 환경과 관련된 다양한 분야에 활용되어 고부가가치의 정보를 제공할 것으로 예상되는데, 특히 시계열 레이더 간섭기법(SAR interferometry, InSAR)의 적용을 통해 댐·보와 같은 수자원시설물의 미세변위 탐지 및 안정성 평가에 효과적으로 사용될 것으로 기대된다. 시계열 영상레이더 간섭기법은 고정산란체를 이용하는 Persistent Scatterer InSAR(PSInSAR) 기법과 분산산란체 기반의 Small BAseline Subset(SBAS) InSAR 기법으로 대표된다. 이 연구에서는 수자원위성에 적합한 수리시설물 시계열 변위 모니터링 알고리즘 개발을 목적으로, Sentinel-1 위성의 C-band SAR 기반 시계열 레이더 간섭기법의 적용성을 평가하고 알고리즘 개발에 고려해야 할 사항들을 분석하였다. 2020년 여름 수재해가 발생한 섬진강댐과 담양댐 및 수변부를 테스트 사이트로 선정하고, 2019년부터 2021년까지의 Sentinel-1 시계열 SAR 영상에 PSInSAR와 SBAS InSAR를 적용하여 시계열 변위를 관측하였다. 댐체에서는 PSInSAR가 SBAS InSAR에 비해 신뢰할 수 있는 시계열 변위를 산출하였다. 그러나 시계열 분석 기간이 길어짐에 따라 PSInSAR 시계열 변위의 정밀도가 낮아지는 경향이 관측되었다. 수변부에서 PSInSAR는 변위 정보를 거의 제공하지 못했다. SBAS InSAR는 수변부의 시계열 변위 모니터링에 효과적이었으나, 여름철 장마 등으로 인해 레이더 간섭도의 긴밀도(coherence)가 낮아질 경우 부정확한 변위를 산출하였다. 앞으로 국내의 다양한 수자원시설물을 대상으로 Sentinel-1 위성을 이용한 시계열 변위 모니터링 알고리즘의 적용성 평가 연구가 진행될 예정이며, 연구 결과를 수자원위성의 관측 특성에 적합한 변위 탐지 알고리즘의 개발에 활용하고자 한다.

• 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 Korea Water Resources Association Conference
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• 2022.05a
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• pp.440-440
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• 2022

1970년대부터 집중 건설 된 우리나라의 다목적댐, 홍수조절댐, 용수전용댐 등의 대형 국가 수자원시설물들의 '고령화'가 급속히 진행되어 수리구조물에 대한 안정성을 주기적으로 파악할 수 있는 정밀안전모니터링 체계 구축이 시급한 시점이다. 주기적인 정밀안전모니터링 방법들 중에는 위성 등을 활용한 원격관측 기술들이 최근 시도되고 있다. 위성 영상레이더(SAR; Synthetic Aperture Radar)는 마이크로파 대역의 전자기파를 송·수신하는 능동센서로 날씨 및 주·야간에 영향을 받지 않고 지표면 관측이 가능한 장점이 있다. 특히, 고정산란체 영상레이더 간섭(PSInSAR; Permanent Scatterer Interferometry SAR)기법은 영상레이더 영상에서 긴밀도(coherence)가 상대적으로 높은 수자원시설물과 같은 고정산란체의 위상(phase) 정보를 이용하여 mm급의 측정민감도로 시계열 변위 분석이 가능하다. 또한, 여러 장의 InSAR 영상을 생성하였기 때문에 DEM 오차, 위성궤도 오차, 대기 성분에 의한 지연 오차 등을 보다 정밀하게 제거할 수 있는 장점이 있다 본 연구에서는 국내 중대형 수자원시설물의 정밀안전모니터링을 위하여 고정산란체 영상레이더 간섭 기법을 영암금호방조제, 영주댐, 소양강댐 등에 적용하여 시계열 변위 분석을 수행하였다. 2014년 11월부터 2022년 3월(현재)까지 획득된 Sentinel-1 SLC(Single Look Complex) 위성자료의 상승(Ascending) 궤도 126장 및 하강(Descending)궤도 187장을 각각 활용하였다. 두 위성궤도를 모두 활용하여 수직, 수평 변위 등 3차원 분석을 수행하였으며, 특히 소양강댐 GPS 관측 자료와 정확도 검증에서 연평균 2mm의 RMSE를 보였다. 이를 통해 위성 원격탐사 기술로도 댐, 보, 방조제와 같은 수자원시설물에 대한 시계열 변위 분석을 통한 댐 안전관리가 가능함을 보여주고 있다. 2025년 발사될 국내 C-밴드 SAR 탑재 수자원위성 개발을 통해 한반도 재방문주기를 단축시킴으로써, 한반도 전역의 수자원시설물 정밀안전진단체계 구축이 가능할 것으로 기대된다.

• Korean Journal of Remote Sensing
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• v.26 no.2
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• pp.143-151
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• 2010

We carried out studies on InSAR techniques for time-series deformation monitoring using multi-temporal SAR. The PSInSAR method using permanent scatterer is much more complicate than the SBAS because it includes many non-linear equation due to the input of wrapped phase. It is conformed the PS algorithm is very sensitive to even PSC selection. On the other hand, the SBAS method using interferogram of small baseline subset is simple but sensitive to the accuracy of unwrapped phase. The SBAS is better method for expecting not significant unwrapping error while PSInSAR is more proper method for expecting local deformation within very limited area. We used 51 ERS-1/2 SAR data during 1992-2000 over Las Vegas, USA for the comparison between PSInSAR and SBAS. Both PSInSAR and SBAS show similar ground deformation value although local deformation seems to be detected in the PSInSAR method only.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.5
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• pp.599-605
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• 2009

Changes of atmospheric pressures cause short- and long-term crustal deformations and thus become error sources in the site positions estimated from space geodesy equipments. In this study, we computed daily displacements due to the atmospheric pressure loading (ATML) at the 14 permanent GPS sites operated by National Geographic Information Institute. And the 10-year GPS data collected at those stations were processed to create a continuous time series of the height estimate. Then, we corrected for the ATML from the GPS height time series to see if the correction changes the site velocity and improves the precision of the time series. While the precision improved by about 4% on average, the velocity change was not significant at all. We also investigated the overall characteristics of the ATML in the southern Korean peninsula by computing the ATML effects at the inland grid points with a $0.5^{\circ}{\times}0.5^{\circ}$ spatial resolution. We found that ATML displacements show annual signals and those signals can be fitted with sinusoidal functions. The amplitudes were in the range of 3-4 mm, and they were higher at higher latitudes and lower at the costal area.

• Water for future
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• v.54 no.6
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• pp.74-77
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• 2021

• 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.

• 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.

• Korean Journal of Remote Sensing
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• v.30 no.6
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• pp.719-730
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• 2014

Small BAseline Subset (SBAS) technique using multi master interferograms can be effective to detect surface deformation in forest area. In this paper, The analysis reveals area of 2-dimension surface deformation at Seguam Island in Aleutian Arc., Alaska. We acquired ERS-1/2 data from track 201 and 473 datasets on Seguam Island from 1992 to 2008. This study analyze surface deformation applying Differential Interferometry Synthetic Aperture Radar (DInSAR) and SBAS time series method using two adjacent tracks. As a results, it was calculated that subsidence -1~2 cm in LOS direction and - 2~3 cm in vertical direction. The horizontal direction was repeated contraction and expansion. The observation of 2-dimension displacements explained the volcanic activity on Seguam island. Also, it is believed to be used for basic data to estimate movements of magma source.

• Korean Journal of Remote Sensing
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• v.40 no.1
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• pp.19-31
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• 2024

Ports are vital social infrastructures that significantly influence both people's lives and a country's economy. In South Korea, the aging of port infrastructure combined with the increased frequency of various natural disasters underscores the necessity of displacement monitoring for safety management of the port. In this study, the time-series displacements of Yeongilman Port and surrounding areas in Pohang, South Korea, were measured by applying Permanent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) to Sentinel-1 SAR images collected from the satellite's ascending (February 2017-July 2023) and descending (February 2017-December 2021) nodes, and the displacement associated with the 2017 Pohang earthquake in the port was analyzed. The southern (except the southernmost) and central parts of Yeongilman Port showed large displacements attributed to construction activities for about 10 months at the beginning of the observation period, and the coseismic displacement caused by the Pohang earthquake was up to 1.6 cm of the westward horizontal motion and 0.5 cm of subsidence. However, little coseismic displacement was observed in the southernmost part of the port, where reclamation was completed last, and in the northern part of the oldest port. This represents that the weaker the consolidation of the reclaimed soil in the port, the more vulnerable it is to earthquakes, and that if the soil is very weakly consolidated due to ongoing reclamation, it would not be significantly affected by earthquakes. Summer subsidence and winter uplift of about 1 cm have been repeatedly observed every year in the entire area of Yeongilman Port, which is attributed to volume changes in the reclaimed soil due to temperature changes. The ground of the 1st and 2nd General Industrial Complexes adjacent to Yeongilman Port subsided during the observation period, and the rate of subsidence was faster in the 1st Industrial Complex. The 1st Industrial Complex was observed to have a westward horizontal displacement of 3 mm and a subsidence of 6 mm as the coseismic displacement of the Pohang earthquake, while the 2nd Industrial Complex was analyzed to have been little affected by the earthquake. The results of this study allowed us to identify the time-series displacement characteristics of Yeongilman Port and understand the impact of earthquakes on the stability of a port built by coastal reclamation.