• Geophysics and Geophysical Exploration
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• v.12 no.3
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• pp.263-267
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• 2009

Recently intrinsic and scattering quality factor ($\varrho_i^{-1}$ and $\varrho_s^{-1}$) was successfully separated from total quality factor ($\varrho_t^{-1}$) on the seismic data of the Korean Peninsula. From this result, we theoretically calculated the expected coda quality factor ($\varrho_{Cexp}^{-1}$) based on multiple scattering model, and compared with other quality factors such as $\varrho_t^{-1}$, $\varrho_i^{-1}$, $\varrho_s^{-1}$, and observed coda quality factor ($\varrho_c^{-1}$) obtained by single scattering model. While the $\varrho_{Cexp}^{-1}$ values are comparable to the $\varrho_i^{-1}$ values, the $\varrho_c^{-1}$ values are close to the values of $\varrho_t^{-1}$ rather than $\varrho_i^{-1}$ and $\varrho_{Cexp}^{-1}$ except for the 24 Hz frequency. This results suggest that the assumption of uniform scatterer in the Korean Peninsula is unrealistic.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3B
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• pp.408-422
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• 2000

In this paper, we propose a generalized vector channel model for wireless communication systems using antenna arrays. The proposed channel model reflects path loss. spatial-temporal variation of shadowing, multipath fading , Doppler effect, spatial distribution of local scatterers and delay spread due to remote dominant scatterers. In addition, we use a discrete ray model in which respective ray signal experiences independent shadowing, fading and Doppler shift, and impinges on antenna arrays at a distinct angle. Based on the proposed mode. we derive the relations on the spatial and temporal correlations of the received signals and implement a spatial channel simulator. By comparing the theoretical values with the simulated ones, we verify the effectiveness of the implemented simulator. The simulator is then used to generate an arbitrary channel impulse response and to analyze the channel characteristics under various environments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.10
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• pp.1062-1068
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• 2014

In this paper, a novel approach estimating target's rotation velocity(RV) is proposed for inverse synthetic aperture radar(ISAR) cross-range scaling(CRS). Scale invariant feature transform(SIFT) is applied to two sequently generated ISAR images for extracting non-fluctuating scatterers. Considering the fact that the distance between target's rotation center(RC) and SIFT features is same, we can set a criterion for estimating RV. Then, the criterion is optimized through the proposed method based on particle swarm optimization(PSO) combined with exhaustive search method. Simulation results show that the proposed algorithm can precisely estimate RV of a scenario based maneuvering target without RC information. With the use of the estimated RV, ISAR image can be correctly re-scaled along the cross-range direction.

• 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.

• 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.

• Korean Journal of Remote Sensing
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• v.37 no.6_1
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• pp.1625-1630
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• 2021

In Bangkok, Thailand, there is an increasing concern for ground subsidence with the rapid urbanization. Given the presence of flood vulnerability due to the flat low-lying topography and proximity to the river delta, it is particularly significant to monitor deformation that can potentially augment flood hazards. In this paper, we have applied persistent scatterer interferometric synthetic aperture radar (PSInSAR) technique to investigate subsidence in Bangkok with the use of Sentinel-1 acquisitions spanning from June 2018 to October 2021. The vertical displacement velocity obtained from both ascending and descending orbits revealed regional-scale subsidence at rates up to 30 mm/yr. In addition, ongoing subsidence was observed in the suburb areas with the localized vertical subsidence exceeding 80 mm. The areas are primarily industrial and agricultural sectors, thus, the ground subsidence detected is probably caused by groundwater withdrawal. However, further work is needed to diagnose the trends of aquifer resources.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.3
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• pp.243-251
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• 2019

Recently, several studies were conducted on the micro-Doppler(MD) phenomenon to identify a warhead from decoys. Both, the warhead and decoy, can be modeled as various shapes and maneuver with their own micro-motion. Their MD phenomenon can be demonstrated by amplitude modulation and phase modulation. Most studies have utilized approximate solutions to express the amplitude modulation regardless of various warhead and decoy shapes. However, the exact solution of the amplitude modulation is required for more effective warhead identification. In this study, we proposed a new modeling method of receiving radar signals from warheads and decoys based on physical optics. The proposed solution was evaluated using an electromagnetic prediction technique and computer-aided design models.

• The Journal of the Acoustical Society of Korea
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• v.38 no.1
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• pp.82-95
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• 2019

In this study, we analyzed the beam time series of ocean reverberation which was conducted in the eastsouthern region of East Sea, Korea during the August, 2015. The reverberation data was gathered by moving research vessel towing LFM (Linear Frequency Modulation) source and triplet receiver array. After signal processing, we analyzed the variation of ocean reverberation level according to the seafloor bathymetry, source/receiver depth and sound speed profile. In addition, we used the normalized data by using cell averaging algorithm and identified the statistical characteristics of seafloor scatterer by using moment estimation method and estimated shape parameter. Also, we analyzed the coincidence of data with Rayleigh and K-distribution probability by Kolmogorov-Smirnov test. The results show that there is range dependency of reverberation according to the bathymetry and also that the time delay and the intensity level change depend on the depths of source and receiver. In addition, we observed that statistical characteristics of similar Rayleigh probability distribution in the ocean reverberation.

• 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 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.