• 대기
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• 제22권2호
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• pp.137-147
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• 2012

The technique of Brightness Temperature Difference (BTD) between 11 and $12{\mu}m$ separates yellow sand dust from clouds according to the difference in absorptive characteristics between the channels. However, this method causes consistent false alarms in many cases, especially over the desert. In order to reduce these false alarms, we should eliminate the background noise originated from surface. We adopted the Background BTD (BBTD), which stands for surface characteristics on clear sky condition without any dust or cloud. We took an average of brightness temperatures of 11 and $12{\mu}m$ channels during the previous 15 days from a target date and then calculated BTD of averaged ones to obtain decontaminated pixels from dust. After defining the BBTD, we subtracted this index from BTD for the Yellow Sand Index (YSI). In the previous study, this method was already verified using the geostationary satellite, MTSAT. In this study, we applied this to the polar orbiting satellite, MODIS, to detect yellow sand dust over Northeast Asia. Products of yellow sand dust from OMI and MTSAT were used to verify MODIS YSI. The coefficient of determination between MODIS YSI and MTSAT YSI was 0.61, and MODIS YSI and OMI AI was also 0.61. As a result of comparing two products, significantly enhanced signals of dust aerosols were detected by removing the false alarms over the desert. Furthermore, the discontinuity between land and ocean on BTD was removed. This was even effective on the case of fall. This study illustrates that the proposed algorithm can provide the reliable distribution of dust aerosols over the desert even at night.

• 센서학회지
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• 제24권4호
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• pp.252-257
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• 2015

This paper proposes a single slope A/D converter (SSADC) that is possible to process the signal of the ultraviolet, visible and infrared rays with a single chip. And the proposed SSADC is a type of single channel ADC. In the conventional SSADC, it is possible to process the only one signal with a kind of the sensor because the speed of the operating frequency and the slope of ramp signal generated by the ramp generator are fixed. In order to improve the disadvantages, a ramp generator which has variable slope in ramp function is designed and $3{\times}1$ MUX(multiplexer) is adopted so that we can change the speed of the operating frequency and the slope of ramp signal. Therefore, the multiple signal processing of the wanted sensors can be possible. The designed circuit is layout by the $0.35-{\mu}m$ CMOS 2-poly 4-metal technology process and is checked through DRC and LVS tools.

• 천문학회보
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• 제42권1호
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• pp.29.1-29.1
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• 2017

I present new near-infrared (NIR) photometry of globular cluster (GC) systems associated to a cD galaxy NGC 4874 in the core of the Coma cluster and 16 early-type galaxies in the Fornax and Virgo clusters of galaxies using the Infrared Channel of the Wide Field Camera 3 (WFC3/IR) on board the Hubble Space Telescope (HST). Combining these high-resolution NIR data with new HST Advanced Camera for Surveys (ACS) optical photometry for NGC 4874 and existing ACS GC catalogs from the ACS Fornax and Virgo Cluster Surveys, I have examined for the first time the GC systems in a statistically significant optical/NIR sample of galaxies spanning a wide range of luminosities and colors. A primary goal of this study is to explore empirically whether the distributions of purely optical and hybrid optical - NIR color indices for extragalactic GCs have different forms and whether the relations between these color indices are nonlinear, indicating that they behave differently with underlying metallicity. I find that some GC systems of large galaxies in our sample show color bimodalities that differ between the optical and optical - NIR colors, in the sense that they have disparate ratios of "blue" and "red" peak GCs, as well as differing ratios in their color dispersions. Consistent with these results, I find empirically that the dependence of hybrid optical-NIR color on purely optical color is nonlinear, with an inflection at intermediate metallicities. These findings underscore the importance of understanding the nature of galaxy-to-galaxy variations in the GC color distributions and color-color relations, as well as the exact forms of the color-metallicity transformations, in interpreting the observational data on GC color bimodality. Our ACS data for NGC 4874 shows that its GC system exhibits a very strong blue tilt, implying a very steep mass-metallicity scaling, and the centroid of this GC system is offset by $4{\pm}1kpc$ from the luminosity center of NGC 4874, in the direction of NGC 4872. Finally, I discuss the asymmetrical GC distribution around a dwarf elliptical galaxy in Coma that has a very high relative velocity with respect to the cluster mean at small clustercentric radius.

• 천문학회보
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• 제36권2호
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• pp.155.1-155.1
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• 2011

The Korea Astronomy and Space Science Institute (KASI) and the Department of Astronomy at the University of Texas at Austin (UT) are developing a near infrared wide-band high resolution spectrograph, IGRINS (Immersion Grating Infrared Spectrograph). The white-pupil design of the instrument optics uses 7 cryogenic mirrors including 3 aspherical off-axis collimators and 4 flat fold mirrors. Two of the 3 collimators are H- and K-band pupil transfer mirrors and they are designed as compensators for the system alignment in each channel. Therefore, their mount design will be one of the most sensitive parts in the IGRINS optomechanical system. The other flat fold mirrors are designed within the limited area. Each of those includes the features of 3 axial hard points and 2 radial hard points with one spring plunger in order for the proper deflection of the mirror. The design work will include the computer-aided 3D modeling and finite element analysis (FEA) to optimize the structural stability and the thermal behavior of the mount models. The mount body will also include a tip-tilt and translation adjustment mechanism to be used as the alignment compensators.

• 대한전자공학회논문지SD
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• 제37권8호
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• pp.42-47
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• 2000

분자선결정성장법을 이용하여 자기구성 양자점들을 high electron mobility transistor (HEMT)의 체널 영역에 삽입하여, 양자점내의 inter-subband transition을 이용한 전파장 적외선 수광소자를 제작하였다. 제작된 소자는 180 K 이상의 온도에서 InAs 양자점의 전자에 대한 강한 구속력으로 인해 낮은 암전류 특성을 보이며 7${\mu}m$에서 11${\mu}m$까지의 넓은 수광영역을 나타내었다. 9.4${\mu}m$에서 peak 광전류가 검출되었으며 이때의 검출율은 $1.93{\times}10^{10}cmHz^{1/2}/W$ 였다. 장파장 적외선 검출에 따른 광전류는 가해진 전압에 대하여 전계효과트랜지스터와 같은 전류-전압 특성을 가지며, 인가된 전압이 증가함에 따라 증가된 암전류에 의하여 광전류가 감소하는 특성을 보여주고 있다.

• 대한원격탐사학회지
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• 제20권4호
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• pp.235-244
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• 2004

본 연구는 SPOT-4 위성의 VEGETATION-1 센서의 가시 채널, 근적외 채널, 단파 적외채널 자료를 이용하여 눈과 구름을 구별하기 위해 새롭게 제시된 알고리즘을 평가하기 위한 것이다. 눈과 구름의 마스크를 위해 전통적으로 이용되고 있는 임계치 방법들은 본 연구에서 좋은 결과를 보여 주지 못하였다 따라서 K-means 군집화 방법이 이러한 임계치 방법 대신 본 연구에서 사용되었다. 군집화에서는 두 임계치 알고리즘을 통합하여 적설과 구름을 그룹화 시켜 동시에 추출한 화소들을 적용하였다. 이것은 전체 영상을 군집화에 적용시킬 때와 비교해 군집화의 과정을 단순화시키고 나아가 정확도를 향상시킬 수 있다. 본 연구는 이러한 과정을 통해 얻어진 결과를 임계치 방법이 적용되었을 때의 결과와 비교함과 동시에 VEGETATION 자료의 분별능력을 평가하였다. 본 연구에서 제시한 방법을 이용하였을 때, 구름과 눈의 분별 능력은 상당히 향상되었다. 분별 오차는 임계치 방법을 사용하였을 때 보다 구름에 대해 19.4% 적설에 대해 9.7% 정도 감소하였다.

• The Journal of Korean Physical Therapy
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• 제36권1호
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• pp.39-44
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• 2024

Purpose: Cybersickness is a type of motion sickness induced by virtual reality (VR) or augmented reality (AR) environments that presents symptoms including nausea, dizziness, and headaches. This study aimed to investigate how cathodal transcranial direct current stimulation (tDCS) alleviates motion sickness symptoms and modulates brain activity in individuals experiencing cybersickness after exposure to a VR environment. Methods: This study was performed on two groups of healthy adults with cybersickness symptoms. Subjects were randomly assigned to receive either cathodal tDCS intervention or sham tDCS intervention. Brain activity during VR stimulation was measured by 38-channel functional near-infrared spectroscopy (fNIRS). tDCS was administered to the right temporoparietal junction (TPJ) for 20 minutes at an intensity of 2mA, and the severity of cybersickness was assessed pre- and post-intervention using a simulator sickness questionnaire (SSQ). Result: Following the experiment, cybersickness symptoms in subjects who received cathodal tDCS intervention were reduced based on SSQ scores, whereas those who received sham tDCS showed no significant change. fNIRS analysis revealed that tDCS significantly diminished cortical activity in subjects with high activity in temporal and parietal lobes, whereas high cortical activity was maintained in these regions after intervention in subjects who received sham tDCS. Conclusion: These findings suggest that cathodal tDCS applied to the right TPJ region in young adults experiencing cybersickness effectively reduces motion sickness induced by VR environments.

• Ecology and Resilient Infrastructure
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• 제6권4호
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• pp.243-249
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• 2019

본 연구는 드론 기반의 초분광 센서를 활용하여 수위변화에 대한 하상재료의 분광정보 차이를 분석하는 것이 목적이다. 하상재료는 흙, 자갈, 호박돌, 갈대, 식생을 대상으로 하였으며 5개 하상재료에 대한 초분광 영상촬영을 실시하고 각 재료의 분광정보를 비교 분석하였다. 수위 변화를 위해 유량조절이 가능한 실험수로를 제작하고 수로 내 하상재료를 설치하였다. 수위 조건은 0.0 m, 0.3 m, 0.6 m이며 수위에 따라 CASE를 구분하였다. 영상촬영 후 각 하상재료별 10개 포인트를 평균한 값을 분석 자료로 사용하였다. 분석 결과 흙, 자갈, 호박돌, 갈대의 파장별 반사율은 비슷한 유형을 보이지만 각 재료별 가시광선과 근적외선 영역에서는 분광정보의 고유특징이 나타났다. 또한 수위가 깊어질수록 가시광선과 근적외선 영역에서 반사율은 감소하고 있으며 감소 비율은 하상재료에 따라 차이가 발생하였다. 하상재료에 대한 고유정보는 향후 하천환경평가를 위한 기초연구 자료로 활용될 것으로 기대된다.

• 대기
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• 제21권2호
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• pp.131-142
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• 2011

Spectral solar irradiances were observed using a visible and UV Multi-Filter Rotating Shadowband Radiometer on the rooftop of the Science Building at Yonsei University, Seoul ($37.57^{\circ}N$, $126.98^{\circ}E$, 86 m) during one year period in 2006. 1-min measurements of global(total) and diffuse solar irradiances over the solar zenith angle (SZA) ranges from $20^{\circ}$ to $70^{\circ}$ were used to examine the effects of clouds and total optical depth (TOD) on enhancing four solar irradiance components (broadband 395-955 nm, UV channel 304.5 nm, visible channel 495.2 nm, and infrared channel 869.2 nm) together with the sky camera images for the assessment of cloud conditions at the time of each measurement. The obtained clear-sky irradiance measurements were used for empirical model of clear-sky irradiance with the cosine of the solar zenith angle (SZA) as an independent variable. These developed models produce continuous estimates of global and diffuse solar irradiances for clear sky. Then, the clear-sky irradiances are used to estimate the effects of clouds and TOD on the enhancement of surface solar irradiance as a difference between the measured and the estimated clear-sky values. It was found that the enhancements occur at TODs less than 1.0 (i.e. transmissivity greater than 37%) when solar disk was not obscured or obscured by optically thin clouds. Although the TOD is less than 1.0, the probability of the occurrence for the enhancements shows 50~65% depending on four different solar radiation components with the low UV irradiance. The cumulus types such as stratoculmus and altoculumus were found to produce localized enhancement of broadband global solar irradiance of up to 36.0% at TOD of 0.43 under overcast skies (cloud cover 90%) when direct solar beam was unobstructed through the broken clouds. However, those same type clouds were found to attenuate up to 80% of the incoming global solar irradiance at TOD of about 7.0. The maximum global UV enhancement was only 3.8% which is much lower than those of other three solar components because of the light scattering efficiency of cloud drops. It was shown that the most of the enhancements occurred under cloud cover from 40 to 90%. The broadband global enhancement greater than 20% occurred for SZAs ranging from 28 to $62^{\circ}$. The broadband diffuse irradiance has been increased up to 467.8% (TOD 0.34) by clouds. In the case of channel 869.0 nm, the maximum diffuse enhancement was 609.5%. Thus, it is required to measure irradiance for various cloud conditions in order to obtain climatological values, to trace the differences among cloud types, and to eventually estimate the influence on solar irradiance by cloud characteristics.

• 대한원격탐사학회지
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• 제25권1호
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• pp.45-59
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• 2009

본 연구에서는 NOAA AVHRR 밝기온도 자료로부터 해수면 온도(SST) 산출에 황사 에어로솔은 미치는 영향을 복사전달 모델을 사용하여 분석하고, SST 복원 알고리즘을 개선하였다. 봄철의 황사에 의한 AVHRR 밝기온도 변화를 모의하기 위한 복사전달 모델의 입력 자료로서 지상 태양광 관측 자료로부터 분석한 황사 에어로솔 광학적 특성 (에어로솔 광학적 두께 및 크기분포)과 라디오 존데 연직분포 자료(기압, 기온, 및 습도)를 이용하였다. 황사 에어로솔은 적외선 복사대에서 흡수에 비해 산란이 매우 큼을 보였으며, 이러한 특징은 지표면에서 방출되는 상향복사량을 산란시켜 대기상부에서 관측되는 밝기 온도를 감소시키는 경향과 관련이 있다. 광학적 두께가 1인 황사의 경우 직하점에서 약 2 K, 위성 천정각이 $50^{\circ}$인 경우에는 약 4 K의 감쇄를 유발하였다. 황사 존재시 AVHRR 적의채널 11, $12{\mu}m$의 밝기온도 차 역시 감소하는 경향을 보이고 있지만 그 값은 미미하였다. 기존 SST 복원 알고리즘은 황사발생시 SST를 실제 값보다도 낮게 산출함을 보였으며, 이를 보정하기 위해 에어로솔 광학적 두께, $11{\mu}m$에서의 밝기온도, 그리고 위성 천정각을 추가하여 알고리즘을 개선하였다. 개선된 SST 복원 알고리즘은 황사의 두께가 1인 경우 2.7 K정도의 오차를 개선하였다.