• Korean Journal of Remote Sensing
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• v.39 no.1
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• pp.65-76
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• 2023

The Gamma Portable Radar Interferometer (GPRI) is a ground-based real aperture radar (RAR) that can acquire images with high spatial and temporal resolution. The GPRI ground-based radar used in this study composes three antennas with a Ku-band frequency of 17.1-17.3 GHz (1.73-1.75 cm of wavelength). It can measure displacement over time with millimeter-scale precision. It is also possible to adjust the observation mode by arranging the transmitting and receiving antennas for various applications: i) obtaining differential interferograms through the application of interferometric techniques, ii) generation of digital elevation models and iii) acquisition of full polarimetric data. We introduced the hardware configuration of the GPRI ground-based radar, image acquisition, and characteristics of the collected radar images. The interferometric phase difference has been evaluated to apply the multi-temporal interferometric SAR application (MT-InSAR) using the first observation campaigns at Pusan National University in Geumjeong-gu, Busan.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.59.2-59.2
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• 2019

Event Horizon Telescope (EHT) aims to resolve the innermost region to the super massive black hole (SMBH) with its extremely high angular resolution (~20-25 uas) and enhanced sensitivity (down to 1-10 mJy) in concert with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm wavelength. This has a great importance as the first observational probe of the black hole shadow which has been theoretically predicted as a ring-like emission affected by the general relativistic effect under a strong gravitational field of SMBH. During the 2017 April 5-11, four nights of EHT observing campaign were carried out towards its primary targets, M87 and $SgrA{\ast}$. To robustly ensure the data processing, independent pipelines for various radio data calibration softwares (e.g., AIPS, HOPS, CASA) have been developed and cross-compared each other. The EHT has also been developing newer interferometric imaging techniques (e.g., eht-imaging-library, SMILI, dynamical imaging), as well as using an established method (CLEAN). With these, the EHT has designed various strategies which will be adopted for convincing imaging results. In this talk, I review how the robustness of EHT data processing and imaging will be validated so that the results can be ensured against well known uncertainties or biases in the interferometric data calibration and imaging.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.530-536
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• 2002

The accurate measurements of thermal expansion coefficients is one of the most important techniques required not only in material science but also in industries. A high precision interferometric dilatometer, using acoustic optical modulator, has been constructed and its performance has been tested. The system consists of a double-path optical heterodyne interferometer and a radiant heating furnace. This provides highly accurate length measurement, and allows rapid heating and cooling method for the specimen. A three longitudinal mode frequency stabilized He-Ne laser, using the secondary beat frequency, is constructed. Its stability is found to be $5{\times}10^{-9}$. The uncertainty in the length measurement is estimated to be of nanometer order in the range between room temperature to 1100 K.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.637-639
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• 2015

The Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) is the first international VLBI array dedicated to high-frequency (23 GHz (K-band) and 43 GHz (Q-band)) observations in East Asia. To evaluate the imagine capability of KaVA, we performed imaging observations of three bright active galactic nuclei (AGNs) known for their complex morphologies: 4C 39.25, 3C 273, and M87 by KaVA at K-/Q-band. Our KaVA images reveal extended outflows with complex substructure such as knots and limb brightening, in agreement with previous observations by other VLBI facilities. Angular resolutions are better than 1.4 and 0.8 milliarcsecond (max) at K-/Q-band, respectively. KaVA achieves a high dynamic range of ~1000, more than three times the value achieved by VERA. We conclude that KaVA is a powerful array with a great potential for the study of AGN outflows, at least comparable to the best existing radio interferometric arrays.

• Smart Structures and Systems
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• v.26 no.3
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• pp.277-290
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• 2020

Disasters, including earthquakes and landslides, have enormous economic and social losses besides their impact on environmental disruption. Iran, and particularly its Western part, is known as an earthquake susceptible area due to numerous strong ground motions. Studying ecological changes due to climate change can improve the public and expert sector's awareness and response to future disastrous events. Synthetic Aperture Radar (SAR) data and Interferometric Synthetic Aperture Radar (InSAR) technologies are appropriate tools for modeling and surface deformation modeling. This paper proposes an efficient approach to detect ground deformation changes using Sentinel-1A. The focal point of this research is to map the ground surface deformation modeling is presented using InSAR technology over Sarpol-e Zahab on 25^th November 2018 as a study case. For surface deformation modeling and detection of the ground movement due to earthquake SARPROZ in MATLAB programming language is used and discussed. Results show that there is a general ground movement due to the Sarpol-e Zahab earthquake between -7 millimeter to +18 millimeter in the study area. This research verified previous researches on the advanced image analysis techniques employed for mapping ground movement, where InSAR provides a reliable tool for assisting engineers and the decision-maker in choosing proper policies in a time of disasters. Based on the result, 574 out of 682 damaged buildings and infrastructures due to the 2017 Sarpol-e Zahab earthquake have moved from -2 to +17 mm due to the 2018 earthquake with a magnitude of 6.3 Richter. Results show that mountainous areas have suffered land subsidence, where urban areas had land uplift.

• Korean Journal of Remote Sensing
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• v.38 no.6_2
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• pp.1589-1605
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• 2022

Phase unwrapping is an essential procedure for interferometric synthetic aperture radar techniques. Accordingly, a lot of phase unwrapping methods have been developed. Deep-learning-based unwrapping methods have recently been proposed. In this paper, we reviewed state-of-the-art deep-learning-based unwrapping approaches in terms of 1) the approaches to predicting unwrapped phases, 2) deep learning model structures for phase unwrapping, and 3) training data generation. The research trend of the approaches to predicting unwrapped phases was introduced by categorizing wrap count segmentation, phase jump classification, phase regression, and deep-learning-assisted method. We introduced the case studies of deep learning model structure for phase unwrapping, and model structure optimization to relate the overall phase information. In addition, we summarized the research trend of the training data generation approaches in the views of phase gradient and noise in the main. And the future direction in deep-learning-based phase unwrapping was presented. It is expected that this paper is used as guideline for exploring future direction of deep-learning-based phase unwrapping research in Korea.

• Journal of The Korean Astronomical Society
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• v.47 no.5
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• pp.195-199
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• 2014

We present a GUI-based interactive Python program, VIMAP, which generates radio spectral index maps of active galactic nuclei (AGN) from Very Long Baseline Interferometry (VLBI) maps obtained at different frequencies. VIMAP is a handy tool for the spectral analysis of synchrotron emission from AGN jets, specifically of spectral index distributions, turn-over frequencies, and core-shifts. In general, the required accurate image alignment is difficult to achieve because of a loss of absolute spatial coordinate information during VLBI data reduction (self-calibration) and/or intrinsic variations of source structure as function of frequency. These issues are overcome by VIMAP which in turn is based on the two-dimensional cross-correlation algorithm of Croke & Gabuzda (2008). In this paper, we briefly review the problem of aligning VLBI AGN maps, describe the workflow of VIMAP, and present an analysis of archival VLBI maps of the active nucleus 3C 120.

• Korean Journal of Remote Sensing
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• v.33 no.6_3
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• pp.1215-1221
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• 2017

SeNtinel's Application Platform (SNAP) is an open source software developed by the European Space Agency and consists of several toolboxes that process data from Sentinel satellite series, including SAR (Synthetic Aperture Radar) and optical satellites. Among them, S1TBX (Sentinel-1 ToolBoX)is mainly used to process Sentinel-1A/BSAR images and interferometric techniques. It provides flowchart processing method such as Graph Builder, and has convenient functions including automatic downloading of DEM (Digital Elevation Model) and image mosaicking. Therefore, if computer memory is sufficient, InSAR (Interferometric SAR) and DInSAR (Differential InSAR) perform smoothly and are widely used recently in the world through rapid upgrades. S1TBX also includes existing SAR data processing functions, and since version 5, the processing capability of KOMPSAT-5 has been added. This paper shows an example of processing the interference technique of KOMPSAT-5 SAR image using S1TBX of SNAP. In the open mine of Tavan Tolgoi in Mongolia, the difference between DEM obtained in KOMPSAT-5 in 2015 and SRTM 1sec DEM obtained in 2000 was analyzed. It was found that the maximum depth of 130 meters was excavated and the height of the accumulated ore is over 70 meters during 15 years. Tidal and topographic InSAR signals were observed in the glacier area near Jangbogo Antarctic Research Station, but SNAP was not able to treat it due to orbit error and DEM error. In addition, several DInSAR images were made in the Iraqi desert region, but many lines appearing in systematic errors were found on coherence images. Stacking for StaMPS application was not possible due to orbit error or program bug. It is expected that SNAP can resolve the problem owing to a surge in users and a very fast upgrade of the software.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.34 no.4
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• pp.357-372
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• 2016

Augustine volcano, located along the Aleutian Arc, is one of the most active volcanoes in Alaska and nearby islands, with seven eruptions occurring between 1812 and 2006. This study monitored the surface displacement before and after the most recent 2006 eruption. For analysis, we conducted a time-series analysis on data observed at the permanent GPS(Global Positioning System) observation stations in Augustine Island between 2005 and 2011. According to the surface displacement analysis results based on GPS data, the movement of the surface inflation at the average speed of 2.3 cm/year three months prior to the eruption has been clearly observed, with the post-eruption surface deflation at the speed of 1.6 cm/year. To compare surface displacements measurement by GPS observation, ENVISAT(Environmental satellite) radar satellite data were collected between 2003 and 2010 and processed the SBAS(Small Baseline Subset) method, one of the time-series analysis techniques using multiple InSAR(Interferometric Synthetic Aperture Radar) data sets. This result represents 0.97 correlation value between GPS and InSAR time-series surface displacements. This research has been completed precise surface deformation using GPS and time-series InSAR methods for a detection of precursor symptom on Augustine volcano.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.629-631
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• 2015

In this proceedings, preliminary results of the KVN Source-Frequency Phase-Referencing (SFPR) observation of 3C 66A and 3C 66B are presented. The motivation of this work is to measure the core-shift of these 2 sources and study the temporal evolution of the jet opacity. Two more sources were observed as secondary reference calibrators and each source was observed at 22, 43, and 86 GHz simultaneously. Our preliminary results show that after using the observations at the lower frequency to calibrate those at the higher frequency of the same source, the residual visibility phases for each source at the higher frequencies became more aligned, and the coherence time became much longer; also, the residual phases for different sources, within 10 degrees angular separations, follow similar trends. After reference to the nearby calibrator, the SFPRed maps were obtained as well as the astrometric measurements, i.e. the combined coreshift. The measurements were found to be affected by structural blending effects because of the large beamsize of KVN, but this can be corrected with higher resolution maps (e.g. KAVA maps).