• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1784-1785
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• 2011

PS(Phase Shift) 방식을 이용하여 3차원 이미지 형상복원 시스템을 구현하였다. PS 방식은 위상을 이동시켜서 얻어진 강도를 arctan 시킴으로써 $-{\pi}{\sim}{\pi}$ 범위의 접혀진(wrapped) 위상을 얻을 수 있으며, 이러한 wrapped 위상을 위상 펼침(unwrapping) 알고리즘을 이용하여 불연속을 제거할 수 있다. 얻어진 위상 정보는 물체의 높이 정보에 비례하기 때문에 위상 분포로써 3차원 형상을 복원할 수 있다. Unwrapping 알고리즘에는 다양한 방식이 있지만 본 연구에서는 LabVIEW 프로그램을 이용하여 Goldstein 알고리즘을 구현하였으며, 감마(Gamma) 효과에 의한 노이즈를 줄이기 위하여 프로젝트와 카메라의 보정(calibration) 프로그램을 개발 및 적용하였다. 이와 같은 실험을 통하여 효과적으로 3차원 형상 정보를 얻을 수 있었다.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.6
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• pp.246-253
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• 2013

Based on the conventional 2-6GHz digital frequency discriminator (DFD) using the phase unwrapping and least-squares techniques, we propose a new 2-18GHz DFD. To compensate for lowered-precision frequency estimation due to the expanded bandwidth, the proposed DFD design employs more delay lines, accordingly accompanying high complexity. Thus, a new computationally efficient frequency estimation algorithm is also presented to overcome such high computational burden. More specifically, the proposed frequency estimation algorithm is basically based on the conventional phase unwrapping technique, along with a new candidates selection for the unwrapped phases under the condition that the phase margin is known. As a result, the computational burden required for the least-squares technique can be reduced. Finally, simulation results are provided to demonstrate the effectiveness of the proposed approach, compared with those of the conventional DFD's.

• Korean Journal of Optics and Photonics
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• v.26 no.3
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• pp.147-154
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• 2015

We propose a method for simultaneously measuring the front and back surface profiles of transparent optical components. The proposed method combines dual-wavelength transmission deflectometry with liquids to record distorted phases at different wavelengths, and then numerically reconstructs the three-dimensional phase information to image the front and back surfaces of the lens. We propose a theoretical model to determine the surface information, and a bifocal lens is experimentally investigated. Unlike conventional transmission deflectometry, our proposed method supports direct observation of the front and back surface profiles of the optical elements.

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.329-334
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• 2006

We have reconstructed 3-dimensional images by using the digital holographic microscope and the Mask-cut phase unwrapping algorithm. Off-axis holograms recorded with a magnified image of the microscopic object lens and reference beam are numerically reconstructed in amplitude and phase image by the Fresnel diffraction approximation. We have simultaneously reconstructed 2-dimensional and 3-dimensional images of the sub-micrometer objects.

• 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.

• 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.

• 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.28 no.2
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• pp.227-235
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• 2012

The InSAR (Interferometric SAR) processing steps for DEM generation consist of the coregistration of two SAR data, interferogram generation, phase filtering, phase unwrapping, phase to height conversion, and geocoding, etc. In this study, we developed the precise algorithm for phase to height conversion, including the ambiguity method taking into account Earth ellipsoid, Schw$\ddot{a}$visch method, and the refined ambiguity method suitable for the interferometric pair with non-parallel obit. From the testing with JERS-1 orbit we found that the height error by traditional ambiguity method reaches to about 40 m during phase to height conversion. The proposed methods are very useful in generating precise InSAR DEM;especially in the case of using non-parallel InSAR pair due to unstable orbit control such as JERS-1 or intentional orbit control such as Cross-InSAR pair between ERS2 and ENVISAT satellite.

• Proceedings of the Optical Society of Korea Conference
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• 2007.02a
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• pp.131-132
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• 2007

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.522-525
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• 2004

Interferometry SAR (InSAR) is a technique to generate topographic map from complex data pairs observed by antennas at different locations. However, to obtain topographic information using InSAR is difficult task because it requires series of complicated process including phase unwrapping and precise recovery of the SAR geometry. Especially, accuracy of the DEM (Digital Elevation Model) produced by repeat pass single SAR pair could be influenced by atmospheric effect. Recently, a new InSAR technique to improve accuracy of DEM has been introduced that utilizes low resolution DEM with a number of SAR image pairs. The coarse DEM plays an important role in reducing phase unwrapping error caused by layover and satellite orbit error. In this study, we implemented DInSAR (Differential InSAR) method which combines low resolution DEMs and ERS tandem pair images. GTOPO30 DEM with 1km resolution, SRTM-3 DEM with 100m resolution, and DEM with 10m resolution derived from 1:25,000 digital vector map were used to investigate feasibility of DInSAR. The accuracy of the DEMs generated both by InSAR and DInSAR was evaluated.