• Economic and Environmental Geology
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• v.35 no.5
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• pp.465-478
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• 2002

We measured subsidences occurred in a coastal reclaimed land, Noksan industrial complex, from May 2, 1996 to February 21, 1998, using 5 interferograms of JERS-1 L-band SAR. SAR with a spatial resolution of about 16 m can detect the two-dimensional distribution of subsidence that is difficult to be estimated from in situ measurements. Accuracy of the subsidences estimated by 2-pass DInSAR was evaluated using the measurements of Magnetic Probe Extensometer (accuracy of :${\pm}$1 mm) installed at 42 stations. DInSAR measurements were well correlated with the field measurements showing an average correlation coefficient of 0.77. The correlation coefficient was further improved to be 0.87 (with RMSE of 1.44 cm) when only highly coherenced (>0.5) pixels were used. The slope of regression line was 1.04, very close to the unit value. In short, DInSAR measurements have a good linear relation with field measurements so that we can effectively detect a subsidence in the coastal reclaimed area especially using pixels of high coherence (>0.5). The maximum accumulated subsidence was about 60 cm in the study area, while the subsidence in the northern and south western areas were less than 20 cm. The resuts show that DInSAR is extremely useful for geotechnical applications as well as observation of natural deformation.

• Korean Journal of Remote Sensing
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• v.31 no.2
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• pp.101-110
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• 2015

Synthetic Aperture Radar Interferometry (InSAR) is affected by various noise source such as atmospheric artifact, orbital error, processing noise etc.. Especially, one of the dominant noise source for long-wave SAR system, such as ALOS PALSAR (L-band SAR satellite) is the ionosphere effect because phase delays on radar pulse through the ionosphere are proportional to the radar wavelength. To avoid misinterpret of phase signal in the interferogram, it is necessary to detect and correct ionospheric errors. Recently, a MAI (Multipler Aperture SAR Interferometry) based ionospheric correction method has been proposed and considered one of the effective method to reduce phase errors by ionospheric effect. In this paper, we introduce the MAI-based method for ionospheric correction. Moreover we propose an efficient method that apply the method over non-coherent area using directional filter. Finally, we apply the proposed method to the ALOS PALSAR pairs, which include the west sea coast region in Korea. A polynomial fitting method, which is frequently adopted in InSAR processing, has been applied for the mitigation of phase distortion by the orbital error. However, the interferogram still has low frequency of Sin pattern along the azimuth direction. In contrast, after we applied the proposed method for ionospheric correction, the low frequency pattern is mitigated and the profile results has stable phase variation values within ${\pm}1rad$. Our results show that this method provides a promising way to correct orbital and ionospheric artifact and would be important technique to improve the accuracy and the availability for L-band or P-band systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.7
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• pp.560-570
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• 2017

Recently, well-known SAR imaging algorithms have been developed to form the focused SAR images for stationary targets. In general, the conventional methods exploit the range variation only defined by the motion of radar platform and SAR geometry. However, for SAR imaging of ground moving targets, the motion of the targets induces an additional range shift, yielding the blurred SAR images. To overcome the problem, in this paper we propose an effective motion compensation algorithm operated under a multi-channel SAR, named along-track interferometry(ATI) and phase unwrapping to directly estimate the motion parameters of the targets. In simulations, 50 Monte-Carlo simulation results show the effectiveness of the algorithm in the presence of noise.

• 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.

• Proceedings of the KSRS Conference
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• 1999.11a
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• pp.474-478
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• 1999

SAR interferometry (InSAR) using the space-borne Synthetic Aperture Radar (SAR) have recently become one of the most effective tools monitoring surface changes caused by landslides, earthquakes, subsidences or volcanic eruption. This study focuses on examining the feasibility of InSAR using the RADARSAT data. Although the RABARSAT SAR with its high resolution and variable incidence angle has several advantages for repeat-pass InSAR, it has two key limitations: first, the orbit is not precisely known; and second, RADARSAT's 24-day repeat pass interval is not very favourable for retaining useful coherence. In this study, two pairs of RADARSAT data in the Nahanni area, NWT, Canada have been tested. We will discuss about the special consideration required on the interferometric processing steps specifically for RADARSAT data including image co-registration, spectral filtering in both azimuth and range, estimation of the interferometric baseline, and correction of the interferogram with respect to the "flat earth" phase contribution. Preliminary results can be summarized as: i) the properly designed azimuth filter based upon the antenna characteristic improves coherence considerably if difference in Doppler centroid of the two images is relatively large; ii) the co-registration process combined by fringe spectrum and amplitude cross-correlation techniques results in optimal matching; iii) the baseline is not always possible to be estimated from the definitive orbit information.

• Proceedings of the KSRS Conference
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• 2000.04a
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• pp.85-90
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• 2000

백두산 지역의 JERS-1 SLC 영상과 볼리비아 지역의 RADARSAT 영상에 대해 각각 interferometry와 radargrammetry를 이용하여 수치표고모형을 제작하였다. Interferometry 는 coregistration, interferogram 작성, phase unwrapping 과정으로 나눠지는데 temporal decorrelation으로 낮은 coherence, 부정확한 궤도정보가 DEM의 정확도를 저하시키는 주요 원인으로 작용하였다. Radargrammetry는 photogrammetry와 동일한 처리과정, 즉 GCP를 이용한 stereo model 설정, 영상 matching, 고도추출단계로 이루어지지만 광학영상 과는 다른 SAR 영상의 기하학적, 방사적 특성이 고려되어야 한다.

• Korean Journal of Remote Sensing
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• v.21 no.4
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• pp.287-302
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• 2005

Digital Elevation Models (DEMs) were generated by ERS-l/2 and JERS-1 SAR interferometry in Daejon area, Korea. The quality of the DEM's was evaluated by the Ground Control Points (GCPs) in city area where GCPs were determined by GPS surveys, while in the mountain area with no GCPs, a 1:25,000 digital map was used. In order to minimize errors due to the inaccurate satellite orbit information and the phase unwrapping procedure, a Differential InSAR (DInSAR) was implemented in addition to the traditional InSAR analysis for DEM generation. In addition, DEMs from GTOPO30, SRTM-3, and 1:25,000 digital map were used for assessment the resolution of the DEM generated from DInSAR. 5-6 meters of elevation errors were found in the flat area regardless of the usage and the resolution of DEM, as a result of InSAR analyzing with a pair of ERS tandem and 6 pairs of JERS-1 interferograms. In the mountain area, however, DInSAR with DEMs from SRTM-3 and the digital map was found to be very effective to reduce errors due to phase unwrapping procedure. Also errors due to low signal-to-noise ratio of radar images and atmospheric effect were attenuated in the DEMs generated from the stacking of 6 pairs of JERS-1. SAR interferometry with multiple pairs of SAR interferogram with low resolution DEM can be effectively used to enhance the resolution of DEM in terms of data processing time and cost.

• 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.

• Korean Journal of Remote Sensing
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• v.27 no.2
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• pp.171-180
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• 2011

MAI (multiple aperture SAR interferometry) method has been recently developed to improve the measurement accuracy of along-track surface deformation. By means of split-beam SAR processing, this novel technique produces forward- and backward-looking interferograms, which are combined to generate an MAI interferogram. The along-track surface deformation can then be derived from the MAI interferogram. The achieved accuracy of the along-track surface deformation is approximately 8 cm for interferograms with a coherence of 0.6. It is commonly recognized that the topographic phase on an MAI interferogram can be ignored. However, in this paper, we have generated an MAI interferogram from an ALOS P ALSAR interferometric pair spanning the 2010 Haiti earthquake, and shown that the topographic phase distortion on the MAI interferogram can reach to about $3.45{\times}10^{-4}$ rad./m. This distortion corresponds to an along-track surface deformation of about 98 cm. We have proposed an efficient method to remove the topographic phase distortion. After correcting the distortion, the topographic phase distortion on the MAI interferogram is reduced to about $7.82{\times}10^{-6}$ rad./m. This means that the proposed method can effectively remove the topographic distortion on the MAI interferogram to improve along-track surface deformation measurement.

• Korean Journal of Remote Sensing
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• v.26 no.2
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• pp.123-131
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• 2010

In this paper we applied Ground-Based Synthetic Aperture Radar(GB-SAR) interferometry to detect artificial displacement of a reflector and performed an atmospheric humidity correction to improve the accuracy. A series of GB-SAR images were obtained using a center frequency of 5.3 GHz with a range resolution of 25 cm and a azimuth resolution of $0.324^{\circ}$, all in full-polarization (HH, VV, VH, HV) modes. A triangular trihedral corner reflector was located 160 m away from the system, and the artificial displacements of 0-40 mm was implemented during the GB-SAR image acquisition. The result showed that the RMS error between the actual and measured displacements, averaged in all polarization data, was 1.22 mm, while the maximum error in case of the 40 mm displacement was 2.72 mm at HH-polarization. After the atmospheric correction with respect to the humidity, the RMS error was reduced to 0.52 mm. We conclude that a GB-SAR system can be used to monitor the possible displacement of artificial/natural scatterers and the stability assessment with sub-millimeter accuracy.