• 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.32 no.6
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• pp.567-577
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• 2016

SqueeSAR is a new technique to combine Persistent Scatterer (PS) and Distributed Scatterer (DS) for deformation monitoring. Although many PSs are available in urban areas, SqueeSAR analysis can be beneficial to increase the PS density in not only natural targets but also smooth surfaces in urban environment. The height of each targets is generally required to remove topographic phase in interferometric SAR processing. The result of PSInSAR analysis to use PS only is not affected by DEM resolution because the height error of initial input DEM at each PSs is precisely compensated in PS processing chain. On the contrary, SqueeSAR can be affected by DEM resolution and precision since it includes spatial average filtering for DS targets to increase a signal-to-noise ratio (SNR). In this study we observe the effect of DEM resolution on deformation measurement by PSInSAR and SqueeSAR. With ALOS-1 PALSAR L-band data, acquired over Daejeon city, Korea, two different DEM data are used in InSAR processing for comparison: 1 m LIDAR DEM and SRTM 1-arc (~30 m) DEM. As expected the results of PSInSAR analysis show almost same results independently of the kind of DEM, while the results of SqueeSAR analysis show the improvement in quality of the time-series in case of 1-m LIDAR DSM. The density of InSAR measurement points was also improved about five times more than the PSInSAR analysis.

• Korean Journal of Remote Sensing
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• v.34 no.2_1
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• pp.283-293
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• 2018

We applied PSInSAR to two SAR satellite (ALOS-1 and COSMO-SkyMed) images and analyzed the difference in displacement observation performance according to sensor characteristics. The building layer was extracted from the digital topographic map, and the PS extracted from the SAR image was classified into two groups(building structure and ground surface) for density analysis. The density of PS extracted from the research area was $0.023point/m^2$ for ALOS-1 PALSAR and $0.1point/m^2$ for COSMO-SkyMed, more than 4 times PS was extracted compared to ALOS-1. In addition, not only the PS density in the building, but also the density in the ground were greatly increased. The average displacement velocity of ALOS-1 PALSAR is within ${\pm}1cm/yr$, while for COSMO-SkyMed it is within ${\pm}0.3cm/yr$. Although it is difficult to make quantitative comparisons because it does not use the data for the same period, it can be said that the accuracy of X-band SAR system is very high compared to the L-band. In consideration of PS observation density and observation accuracy of displacement, X-band SAR data is very effective in research where it is important to acquire useful signals from the ground surface, such as ground subsidence and sinkhole.

• Korean Journal of Remote Sensing
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• v.34 no.4
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• pp.703-708
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• 2018

In recent years, subsidence due to excessive groundwater withdrawal is a major problem in the Kathmandu Basin. In addition, on 25 April 2015, the basin experienced large crustal displacements caused by Mw 7.8 Gorkha earthquake. In this study, we applied StaMPS- Persistent Scatterer InSAR (StaMPS PS-InSAR) technique to estimate the spatio-temporal displacements in the basin after the mainshock. 34 Sentinel-1 C-band SAR data are used for measuring subsidence velocity during 2015-2017. We found the maximum subsidence velocity of about 9.02 cm/year and mean subsidence rate of about 8.06 cm/year in the line of sight direction, respectively, in the central part of the basin.

• Journal of the Korean Geosynthetics Society
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• v.21 no.4
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• pp.55-67
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• 2022

In this paper, fundamentals and recent development of the interferometric synthetic aperture radar, known as InSAR, technique for measuring ground deformation through satellite image analysis are presented together with case histories illustrating its applicability to urban ground deformation monitoring. A study area in Korea was selected and processed based on the muti-temporal time series InSAR analysis, namely SBAS (Small Baseline Subset)-InSAR and PS (Persistent Scatterers)-InSAR using Sentinel-1A SAR images acquired from the year 2014 onward available from European Space Agency Copernicus Program. The ground settlement of the study area for the temporal window of 2014-2022 was evaluated from the viewpoint of the applicability of the InSAR technique for urban infrastructure settlement monitoring. The results indicated that the InSAR technique can reasonably monitor long-term settlement of the study area in millimetric scale, and that the time series InSAR technique can effectively measure ground settlement that occurs over a long period of time as the SAR satellite provides images of the Korean Peninsula at regular time intervals while orbiting the earth. It is expected that the InSAR technique based on higher resolution SAR images with small temporal baseline can be a viable alternative to the traditional ground borne monitoring method for ground deformation monitoring in the 4^th industrial era.

• Journal of the Korean Geotechnical Society
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• v.38 no.11
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• pp.43-54
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• 2022

The settlement at the railroad foundation is often the leading cause of track irregularity and potential derailment. The control of such deformation is considered necessary in track maintenance practice. Nevertheless, the monitoring process performed by in situ surveying requires an excessive amount of manpower and cost. The InSAR, a remote sensing technique by RADAR satellite, is used to overcome such a burden. The PS-InSAR technique is preferred for a long-term precise monitoring method. However, this study aims to obtain relatively brief analysis results from only two satellite images using the D-InSAR technique, while a minimum of 25 images are required for PS-InSAR. This study verifies the precision of D-InSAR within a few millimeters by inspecting railroad facilities and land settlements in Korea Railroad Research Institute's test track with images from TerraSAR-X Satellite. Multiple corner reflectors were adopted and installed on an embankment and the building roof to raise the surface reflectivity. Those reflectors were slightly adjusted periodically to verify the detecting performance. The results revealed the optimum distance between corner reflectors. Further, the deformation of railway tracks, slopes, and concrete structures was analyzed successively. In conclusion, this study indicates that the D-InSAR technique effectively monitors the short-term deformation of a broad area such as railway structures.

• Disaster Prevention Review
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• v.20 no.1
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• pp.28-34
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• 2018

• Economic and Environmental Geology
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• v.37 no.5
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• pp.509-519
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• 2004

The ground subsidence that occurred in the abandoned coal mining area, Gaeun, Korea, was observed using 25 JERS-1 SAR interferograms from November 1992 to October 1998. We carried out measurements on a subset of image pixels corresponding to point-wise stable reflectors(PS: permanent scatterer) by exploiting a long temporal series of interferometric phases and compared it with the distribution map of in situ examined crack level. PSs could be identified by means of amplitude dispersion index and coherence of the interferograms and the density of PS was much higher in an urban area than in a mountainous region. The measured subsidence rate represented the average velocity in a period of image acquisition and excluded complex nonlinear displacements such as an abrupt collapse. The mean line-of-sight velocity in the study area is 0.19cm/yr and the estimation error is 0.18cm/yr. The center of the abandoned Gaeun coal mine(0.49cm/yr) and the area opposite Gaeun station(1.66cm/yr) were observed as the most highly subsiding areas.

• Korean Journal of Remote Sensing
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• v.27 no.5
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• pp.521-534
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• 2011

The high-resolution X-band SAR systems such as COSMO-SkyMED and TerraSAR-X have been launched recently. In addition KOMPSAT-5 will be launched in the early of 2012. In this study we developed the new method for persistent scatterer candidate (PSC) selection and network construction, which is more suitable for PSInSAR analysis using multi-temporal X-band SAR data. PSC selection consists in two main steps: first, selection of initial PSCs based on amplitude dispersion index, mean amplitude, mean coherence. second, selection of final PSCs based on temporal coherence directly estimated from network analysis of initial PSCs. To increase the stability of network the Multi- TIN and complex network for non-urban area were addressed as well. The proposed algorithm was applied to twenty-one TerraSAR-X SAR of New Orleans. As a result many PSs were successfully extracted even in non-urban area. This research can be used as the practical application of KOMPSAT-5 for surface displacement monitoring using X-band PSInSAR.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.138-141
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• 2007

The permanent scatterer SAR interferometry (PSInSAR) technique has been developed more recently and has been applied to monitor slow but consistent ground subsidence. Since PSInSAR has the advantages in terms of baseline and temporal decorrelation, PSInSAR technique using X-band may also provide useful information about a ground deformation in detail. We developed our codes for a persistent scatterer analysis, and then apply to ERS-1/2 C-band data over Las Vegas in order to validate our new developed algorithm. Based on this test, PS technique using X-band observation such as TerraSAR-X or KOMSAT 5 will be developed.