• Journal of Astronomy and Space Sciences
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• 제40권1호
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• pp.1-10
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• 2023

Korea Polar Research Institute (KOPRI) and Korea Astronomy and Space Institute (KASI) have been participating in the European Incoherent Scatter (EISCAT) Scientific Association as an affiliate institution in order to observe the polar ionosphere since 2015. During the period of December 16-21, 2016 and January 3-9, 2018, the observations for the polar ionospheric parameters such as the electron density profiles, ion drift, and electron/ion temperature are carried out in the polar cap/cusp region by the EISCAT Svalbard radar (ESR). The purpose of the observations is to investigate the characteristic of the winter ionosphere in the dayside polar cap/cusp region. In this paper, we briefly report the results of the ESR observations for winter daytime ionosphere and also the simultaneous observations for the ionosphere-thermosphere system together with the balloon-borne instrument High-Altitude Interferometer WIND Experiment (HIWIND) performed by the High Altitude Observatory (HAO), National Center for Atmospheric Research (NCAR). We further introduce our research activities using long-term EISCAT observations for the occurrence of ion upflow and the climatology of the polar ionospheric density profiles in comparison with the mid-latitude ionosphere. Finally, our future research plans will briefly be introduced.

• 한국통신학회논문지
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• 제24권12A호
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• pp.1966-1973
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• 1999

본 논문에서는 차세대 통신 인프라로 부상하고 있는 성층권 통신시스템에 대하여 간략하게 소개하며 이를 통해 고품질의 서비스를 제공하기 위한 방법으로 다양한 형태의 오류정정부호를 제안한다. 성층권 통신시스템은 고주파수 특성에 의한 강우 감쇠, 대기 산란 등으로 인해 신호전력의 저하가 심하므로 부호화 이득이 높은 연접부호의 사용이 바람직하며 이러한 연접부호를 설계하기 위해 본 논문에서는 성층권 통신시스템 국외 개발업체가 제안한 연접부호와 최근의 부호이론 분야에서 각광받고 있는 반복복호법을 사용한 다양한 형태의 연접부호들의 성능을 비교 분석한다.

• 한국전자통신학회논문지
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• 제16권3호
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• pp.423-428
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• 2021

윈드프로파일러와 라디오존데 관측을 함께 하고 있는 북강릉과 창원의 윈드프로파일러에 대한 성능을 평가하였다. 2019년 12월부터 2020년 11월까지 1년간 고도별·월별 풍속 자료 수집률을 조사하고, 라디오존데의 풍속과 비교하였다. 두 관측 지점의 정상 자료 수집률은 최저 관측 고도에서 낮다가 증가하였고, 2 km 이상부터 다시 감소하였다. 여름철(6, 7, 8월)의 수집률이 높았고, 겨울철(12, 1, 2월)의 수집률이 낮았다. 라디오존데와 비교한 결과는 고층 모드에서 0.9, 저층 모드에서 0.8의 높은 상관관계를 보였다.

• 한국입자에어로졸학회지
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• 제10권4호
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• pp.169-176
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• 2014

본 연구에서는 대기 중 연직방향의 혼합에 의한 PAHs 성분의 농도 분포 특성을 파악하였다. 모든 측정기간 동안 지상에서의 총 PAHs 농도가 상공에서 관측한 결과보다 높았고, 약 4-5배정도 높았다. 고도별 PAHs성분들의 구성비율은 동일 측정날에서는 PAH 성분들의 구성비율이 유사하였지만, 측정일별로는 다른 분포를 보였다. 이를 통해 상공에서의 PAH 성분들의 농도분포는 지상의 PAH 성분들의 농도분포와 관련이 있음을 확인하였다. 특정 PAH 성분들의 분포비율을 바탕으로 지상과 상공의 PAHs 분포 및 배출특성을 살펴본 결과, 상공의 PAH 성분들은 지상에 비해 대기 체류시간이 상대적으로 높았고, 지상과 상공 모두 동일하게 바이오매스 및 석탄의 연소에 의한 배출영향이 지배적인 것을 확인할 수 있었다. 본 연구는 국내에서는 처음으로 고도별 입자상 PAH 성분들의 농도 특성을 파악하였다는데 의의가 있다. 하지만, 상공에서의 PAHs 농도의 보다 명확한 특성파악을 위해서는 고도별 PAHs 농도 프로파일이 작성되어야 한다. 따라서, 동일 측정일에 다양한 고도에서의 입자 시료의 확보가 요구된다.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2004년도 총회 및 춘계학술발표회
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• pp.408-412
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• 2004

A total of 23 springs distributed in the southern and northern sides of Mt. Hala in Jeju Island were seasonally sampled and analyzed for their major ion chemistry and oxygen and hydrogen isotope compositions to investigate their hydrogeochemical and isotopic characteristics. Dissolved ion concentrations of the south-side springs slightly increase with decreasing altitude. This indicates that dissolved ion concentrations of groundwater recharged at higher altitudes increase by water-rock interaction during the downgradient migration of groundwater through highly permeable volcanic aquifer. Dissolved ion concentrations of the north-side springs also slightly increase with decreasing altitude, but dramatically increase at ～300 m.a.s.l. This may indicate a sudden input of contaminants to the north-side groundwater system around ～300 m.a.s.l. Springs located in areas above ～300 m.a.s.l. have very low concentrations of dissolved ions, showing little seasonal variations. Whereas springs located in areas below ～300 m.a.s.l. show a big seasonal variation in the concentration of dissolved ions. Seasonal variation of oxygen isotope compositions of springs is ～3$\textperthousand$ for high-altitude springs (～1700 m.a.s.l.) and is ～2$\textperthousand$ near shore, indicating an attenuation of the variation through mixing with other groundwater bodies during migration.

• 한국유체기계학회 논문집
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• 제14권1호
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• pp.42-47
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• 2011

Measurement uncertainty analysis of fuel flow using turbine flowmeter was performed for the case of altitude engine test. SAE ARP4990 was used as the fuel flow calculation procedure, as well as the mathematical model for the measurement uncertainty assessment. The assessment was performed using Sensitivity Coefficient Method. 11 parameters involved in the calculation of the flow rate were considered. For the given equipment setup, the measurement uncertainty of fuel flow was assessed in the range of 1.19~1.86 % for high flow rate case, and 1.47~3.31 % for low flow rate case. Fluctuation in frequency signal from the flowmeter had the largest influence on the fuel flow measurement uncertainty for most cases. Fuel temperature measurement had the largest for the case of low temperature and low flow rate. Calibration of K-factor and the interpolation of the calibration data also had large influence, especially for the case of very low temperature. Reference temperature, at which the reference viscosity of the sample fuel was measured, had relatively small contribution, but it became larger when the operating fuel temperature was far from reference temperature. Measurement of reference density had small contribution on the flow rate uncertainty. Fuel pressure and atmospheric pressure measurement had virtually no contribution on the flow rate uncertainty.

• 항공우주시스템공학회지
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• 제9권2호
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• pp.57-62
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• 2015

The satellite orbit is continuously changing due to space environment. Especially for low earth orbit, atmospheric drag plays an important role in the orbit altitude decay. Recently, solar activities are expected to be high, and relevant events are occurring frequently. In this paper, analysis on the impact of geomagnetic storm on LEO satellite orbit is presented. For this, real flight data of KOMPSAT-2, KOMPSAT-3, and KOMPSAT-5 are analyzed by using the daily decay rate of mean altitude is calculated from the orbit determination. In addition, the relationship between the solar flux and geomagnetic index, which are the metrics for solar activities, is statistically analyzed with respect to the altitude decay. The accuracy of orbit prediction with both the fixed drag coefficient and estimated one is examined with the precise orbit data as a reference. The main results shows that the improved accuracy can be achieved in case of using estimated drag coefficient.

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1817-1825
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• 2020

Background: Cosmic ray-induced particles can lead to failure of semiconductors packaged for export during air transport. This work performed MCNP 6.2 simulations to optimize shielding against neutrons and protons induced by cosmic radiation Methods and materials: The energy spectra of protons and neutrons by incident angle at the flight altitude were determined using atmospheric cuboid model. Various candidates for the shielding materials and the geometry of the Unit Load Device Container were evaluated to determine the conditions that allow optimal shielding at all sides of the container. Results: It was found that neutrons and protons, at the flight altitude, generally travel with a downward trajectory especially for the particles with high energy. This indicated that the largest number of particles struck the top of the container. Furthermore, the simulation results showed that, among the materials tested, borated polyethylene and stainless steel were the most optimal shielding materials. The optimal shielding structure was also determined with the weight limit of the container in consideration. Conclusions: Under the determined optimal shielding conditions, a significantly reduced number of neutrons and protons reach the contents inside the container, which ultimately reduces the possibility of semiconductor failure during air transport.

• 한국군사과학기술학회지
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• 제20권3호
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• pp.345-351
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• 2017

A wind tunnel test for the scaled parachute models was performed to verify aerodynamic characteristics for practical usage of Korean low cost low altitude aerial delivery system. The cruciform shaped cargo parachute models for heavy and light weight were ejected into wind tunnel test section; and the drag forces acting on the models in steady condition were measured in accordance with velocity. Also, the maximum opening forces during inflation were obtained and captured by a high speed camera to analyze the inflation characteristics and evaluate the design of the low cost aerial delivery system. The results showed a reliable stability and met the design requirement of delivery operation system for R.O.K Air Force.

• KIEAE Journal
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• 제12권1호
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• pp.113-118
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• 2012

The photovoltaic is one of the most important sustainable technologies appliable to architectures. The power performance mainly depends on the installation conditions of them. This study aims to evaluate the power performance of photovoltaic system by the installation conditions, the tracking methods and reflecting mirrors. For the study, the Solar Pro computer simulations have been conducted on installation angles, solar azimuth and solar altitude. Also, the field mock-up tests are performed to of its application to verify the simulation results. Both the results of the experiment and the simulation have proved that the efficiency of 90-degree fixed angle method was higher than that of 30-degree fixed angle, the efficiency of altitude tracking was better than that of azimuth tracking method, and changing both the altitude and the azimuth together is more efficient rather than the shortened tracing way. In addition, the light-concentrating method in which the incidence angle of the sun is controlled by an adhered reflector has been analyzed to have better efficiency than the general method of tracing according to the orbit of the sun. Therefore, this thesis is expected to offer the basic data to set a more effective tracing-type of photovoltaic power generation system in the future. For this, more researches are to be conducted hereafter on a high efficiency drive motor and the establishment of an economic system.