• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.112.2-112.2
• /
• 2012

For the study of fine-scale structure and dynamics in the solar chromosphere, the Fast Imaging Solar Spectrograph (FISS) was installed in 1.6m New Solar Telescope at Big Bear Solar Observatory in 2010. The instrument, installed at a vertical table of the Coude lab, is properly working and producing data for science. From the analysis of the data, however, we noticed that a couple of problems exist that deteriorate image quality : lower light level and poorer resolution of the CaII band data. After several tests, we found that the relay optics at the right position is crucial role for the spatial resolution of raster-scan images. By using resolution target, we re-aligned relay optics and other components of the spectrograph. Here we present the result of optical test and new data taken by the FISS.

• Journal of The Geomorphological Association of Korea
• /
• v.28 no.4
• /
• pp.15-30
• /
• 2021

This study analyzed the changes in land-cover and sedimentary environment before and after flooding through drone images and sediment analysis for the Seomjin River Chimsil Wetland. The results showed that the area of some land-covers such as sand bar, grass, and trees were continuously changed. The acidity level of the sediments in the Seomjin River Chimsil Wetland was weakened gradually by flooding and EC was also decreased. The levels of organic matter, effective phosphoric acid, and CEC, however, were fluctuating depending on branches, which seems to be the result of landization as new sedimentary environment was developed and vegetation was settled after the flood. Average mean size of river sediments was found to be fine sand, and it exhibited various particle size characteristics from granule to medium silt depending on the location. As the sedimentary environment changed due to the effects of floods and typhoons, the particles were granulated or grain refined depending on the position. In the Seomjin River Chimsil Wetland, there were factors that could interfere with geomorphic development and sedimentary environment, contamination sources in and around the wetland, and natural threat factors. Therefore, in this study, a conservation and management plan was proposed to remove these threat factors and to preserve the scarcity, naturalness, and dynamics of Seomjin River Chimsil Wetland.

• Korean Journal of Remote Sensing
• /
• v.35 no.4
• /
• pp.573-587
• /
• 2019

A multi-temporal approach using remotely sensed time series data obtained over multiple years is a very useful method for monitoring land covers and land-cover changes. While spectral-based methods at any particular time limits the application utility due to instability of the quality of data obtained at that time, the approach based on the temporal profile can produce more accurate results since data is analyzed from a long-term perspective rather than on one point in time. In this study, a multi-temporal approach applying a multi-periodic harmonic model is proposed for classification of remotely sensed data. A harmonic model characterizes the seasonal variation of a time series by four parameters: average level, frequency, phase, and amplitude. The availability of high-quality data is very important for multi-temporal analysis.An satellite image usually have many unobserved data and bad-quality data due to the influence of observation environment and sensing system, which impede the analysis and might possibly produce inaccurate results. Harmonic analysis is also very useful for real-time data reconstruction. Multi-periodic harmonic model is applied to the reconstructed data to classify land covers and monitor land-cover change by tracking the temporal profiles. The proposed method is tested with the MODIS and GOCI NDVI time series over the Korean Peninsula for 5 years from 2012 to 2016. The results show that the multi-periodic harmonic model has a great potential for classification of land-cover types and monitoring of land-cover changes through characterizing annual temporal dynamics.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.15 no.1
• /
• pp.172-183
• /
• 2012

In 2011, floods were at the worst stage of devastation in Chao Phraya river basin of Thailand. The purpose of this study is to trace the flood inundation area around Chao Phraya river basin by using Terra MODIS image because it has the ability of spatiotemporal dynamics. The MODIS indices, which included the enhanced vegetation index(EVI), land surface water index(LSWI), and the difference in the values of EVI and LSWI(DVEL), were extracted from MODIS product MOD09 8-day composite datasets with a spatial resolution of 500m from Jul. 29, 2011 to Jan. 09, 2012. We found that combined application of EVI, LSWI, and DVEL was suitable for monitoring flood inundation. For the extracted flood inundation area and water-related area. The result can be used to acquire the flood inundation data scattered and demonstrate the potential for the use of MODIS data for temporal and spatial detection of flood effects.

• Korean Journal of Remote Sensing
• /
• v.29 no.1
• /
• pp.45-55
• /
• 2013

Campbell Glacier in East Antarctica is one of the major glaciers that flow into Terra Nova Bay. It is necessary to estimate accurate extent and flow velocity of Campbell Glacier which influences the dynamics of mass balance of East Antarctic Ice Sheet. However, few studies on Campbell Glacier have been performed since 1990s. In this study, we obtained a total of 59 COSMO-SkyMed SAR images over Campbell Glacier from June 2010 to January 2012. We estimated variations in the extent of Campbell Glacier Tongue and flow velocity of Campbell Glacier by applying the image digitizing and the offset tracking by image matching. Although the extent of Campbell Glacier Tongue decreased in summertime due to ice calving and increased in wintertime, the variation in the extent was very small. Campbell Glacier Tongue retained mean extent of 75.5 $km^2$. The ice discharge of Campbell Glacier Tongue was estimated to be $0.58{\pm}0.12km^3/yr$, which was bigger than in 1989. The flow velocity over Campbell Glacier Tongue was estimated to be from 181 to 268 m/yr that was faster than in 1988-1989, which contributed to the increase in the ice discharge of the glacier.

• Journal of computational fluids engineering
• /
• v.20 no.3
• /
• pp.94-103
• /
• 2015

The turbulent flow characteristics in the channel flow are investigated using large eddy simulation(LES) of FDS code, built in NIST(USA), in which the near-wall flow is solved by Werner-Wengle wall function. The periodic flow condition is applied in streamwise direction to get the fully developed turbulent flow and symmetric condition is applied in lateral direction. The height of the channel is H=1m, and the length of the channel is 6H, and the lateral length is H. The total grid is $32{\times}32{\times}32$ and $y^+$ is kept above 11 to fulfill the near-wall flow requirement. The Smagorinsky model is used to solve the sub-grid scale stress. Smagorinsky constant $C_s$ is 0.2(default in FDS). Three cases of Reynolds number(10,700, 26,000, 49,000.), based on the channel height, are analyzed. The simulated results are compared with direct numerical simulation(DNS) and particle image velocimetry(PIV) experimental data. The linear low-Re eddy viscosity model of Launder & Sharma and non-linear low-Re eddy viscosity model of Abe-Jang-Leschziner are utilized to compare the results with LES of FDS. Reynolds normal stresses, Reynolds shear stresses, turbulent kinetic energys and mean velocity flows are well compared with DNS and PIV data.

• Journal of the Regional Association of Architectural Institute of Korea
• /
• v.20 no.6
• /
• pp.41-46
• /
• 2018

The context of innovation in which we evolve today, subtracts us in a spacial reality and virtuality (digital) that aimed less and less to interact with natural processes which could converge to new possible relationships in the world. We constantly live in presence of fluctuations and imperceptible natural energies (wind, solar radiation, etc.) defined by flows, their own physicality, which remains without being virtual, elusive. This study first outlines how these energies already exploited within the framework of production, could be thought as interactive of our habitat's space dimension, as a prolongation of a physical and material environment built by men and for men, giving rise to new social, cultural dynamics, and making natural complexity of our space vivid, comprehensible with new visual and physical clues. In recent days, where lifestyles are changing, architecture no longer needs to limit its scope of creation to only built structures. Based on a deeper understanding of human and through new potential advanced technologies (kinetic system, etc), it is time to fundamentally diagnose what environments or devices contribute to our lives. Architecture becomes ${\ll}interface{\gg}$, step up its fundamental role, and newly defines the sturdy image and tectonics of existing environment, establishing a stance to search for a new typology. In the end, building will show two simultaneous and distinctive connections related to its physical existence: reality in its function and irreductibility, in its ability to forge new dynamic connections with its environment, hybridizing the spatial dimension to a new form of physicality, adaptive and incessantly flexible in the dimension time, becoming a vessel for ever changing contemporary lifestyles.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.133-137
• /
• 2015

The Galactic center uniquely provides opportunities to resolve how star clusters form in neutral gas overdensities engulfed in a large-scale accretion flow. We have performed sensitive Green Bank 100m Telescope (GBT), Karl G. Jansky Very Large Array (JVLA), and Submillimeter Array (SMA) mapping observations of molecular gas and thermal dust emission surrounding the Galaxy's supermassive black hole (SMBH) Sgr $A^{\ast}$. We resolved several molecular gas streams orbiting the center on ${\gtrsim}10$ pc scales. Some of these gas streams appear connected to the well-known 2-4 pc scale molecular circumnuclear disk (CND). The CND may be the tidally trapped inner part of the large-scale accretion flow, which incorporates inflow via exterior gas filaments/arms, and ultimately feeds gas toward Sgr $A^{\ast}$. Our high resolution GBT+JVLA $NH_3$ images and SMA+JCMT 0.86 mm dust continuum image consistently reveal abundant dense molecular clumps in this region. These gas clumps are characterized by ${\gtrsim}100$ times higher virial masses than the derived molecular gas masses based on 0.86 mm dust continuum emission. In addition, Class I $CH_3OH$ masers and some $H_2O$ masers are observed to be well associated with the dense clumps. We propose that the resolved gas clumps may be pressurized gas reservoirs for feeding the formation of 1-10 solar-mass stars. These sources may be the most promising candidates for ALMA to probe the process of high-mass star-formation in the Galactic center.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.43 no.8
• /
• pp.757-764
• /
• 2015

Mathematical modeling of focal plane compensation device in the small earth-observation satellite camera has been conducted experimently for compensation of micro-vibration disturbance. The PZT actuators are used as control actuators for compensation device. It is quite difficult to build up mathematical model because of hysteresis characteristic of PZT actuators. Therefore, the compensation device system is assumed as a $2^{nd}$ order linear system and modeled by using MATLAB System Identification Toolbox. It has been found that four linear models of compensation device are needed to meet 10% error in the input frequency range of 0~50Hz. These models describe accurately the dynamics of compensation device in the 4 divided domains of the input frequency range of 0~50Hz, respectively. Micro-vibration disturbance can be compensated by feedback control strategy of switching four models appropriately according to the input frequency.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.31 no.5
• /
• pp.479-486
• /
• 2011

In image-based CFD modeling of carotid bifurcation hemodynamics, it is often not possible (or at least not convenient) to impose measured velocity profiles at the common carotid artery inlet. Instead, fully-developed velocity profiles are usually imposed based on measured flow rates. However, some studies reported a pronounced influence of inflow boundary conditions that were based on actual velocity profiles measured by magnetic resonance imaging which showing the unusual presence of a high velocity band in the middle of the vessel during early diastole inconsistent with a Dean-type velocity profile. We demonstrated that those velocity profiles were induced by the presence of modest secondary curvature of the inlet and set about to test whether such more "realistic" velocity profiles might indeed have a more pronounced influence on the carotid bifurcation hemodynamics. We found that inlet boundary condition with axisymmetric fully-developed velocity profile(Womersley flow) is reasonable as long as sufficient CCA inlet length of realistic geometry is applied.