• 대한토목학회논문집
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• 제33권6호
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• pp.2601-2610
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• 2013

정밀단독측위(PPP)의 정확도에 영향을 주는 주요변수는 위성궤도력의 정확도, 위성시계오차, 관측자 환경에 종속된 오차(전리층 및 대기층 지연, multipath, tides 등) 및 이들과 관련한 모호정수의 해석 문제 등이다. 따라서 정밀단독측위의 정확도를 향상시키기 위해서는 여러 주파수의 GNSS 관측 자료에 정밀한 위성궤도 및 시계 보정정보와 관측자에 종속된 보정정보를 적용하여 전리층지연 및 모호정수를 실시간 해석해야 한다. 현재, 지역 및 광역 실시간 GNSS 관측망으로 부터 정밀 보정정보를 제공하는 여러 해석센터가 있다. 본 연구는 지역 또는 광역 GNSS 관측망의 해석센터들로부터 산출된 RTCM 보정정보를 NTRIP으로 수신하여 실시간으로 검사점에 개별 및 조합 적용하고 표준단독측위(SPP) 및 다양한 보정정보의 적용에 따른 정밀단독측위의 정확도를 시간대별로 비교 분석하여 GNSS위성에 의한 실시간 절대측위의 정확도를 검토하였다.

• 한국환경과학회지
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• 제25권7호
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• pp.1029-1042
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• 2016

The initial and boundary conditions are important factors in regional chemical transport modeling systems. The method of generating the chemical boundary conditions for regional air quality models tends to be different from the dynamically varying boundary conditions in global chemical transport models. In this study, the impact of real time Copernicus atmosphere monitoring service (CAMS) re-analysis data from the modeling atmospheric composition and climate project interim implementation (MACC) on the regional air quality in the Korean Peninsula was carried out using the community multi-scale air quality modeling system (CMAQ). A comparison between conventional global data and CAMS for numerical assessments was also conducted. Although the horizontal resolution of the CAMS re-analysis data is not higher than the conventionally provided data, the simulated particulate matter (PM) concentrations with boundary conditions for CAMS re-analysis is more reasonable than any other data, and the estimation accuracy over the entire Korean peninsula, including the Seoul and Daegu metropolitan areas, was improved. Although an inland area such as the Daegu metropolitan area often has large uncertainty in PM prediction, the level of improvement in the prediction for the Daegu metropolitan area is higher than in the coastal area of the western part of the Korean peninsula.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.236-238
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• 2006

An algorithm for detection of yellow sand aerosols has been developed with infrared bands from Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-functional Transport Satellite-1 Replacement (MTSAT-1R) data. The algorithm is the hybrid algorithm that has used two methods combined together. The first method used the differential absorption in brightness temperature difference between $11{\mu}m$ and $12{\mu}m$ (BTD1). The radiation at 11 ${\mu}m$ is absorbed more than at 12 ${\mu}m$ when yellow sand is loaded in the atmosphere, whereas it will be the other way around when cloud is present. The second method uses the brightness temperature difference between $3.7{\mu}m$ and $11{\mu}m$ (BTD2). The technique would be most sensitive to dust loading during the day when the BTD2 is enhanced by reflection of $3.7{\mu}m$ solar radiation. We have applied the three methods to MTSAT-1R for derivation of the yellow sand dust and in conjunction with the Principle Component Analysis (PCA), a form of eigenvector statistical analysis. As produced Principle Component Image (PCI) through the PCA is the correlation between BTD1 and BTD2, errors of about 10% that have a low correlation are eliminated for aerosol detection. For the region of aerosol detection, aerosol index (AI) is produced to the scale of BTD1 and BTD2 values over land and ocean respectively. AI shows better results for yellow sand detection in comparison with the results from individual method. The comparison between AI and OMI aerosol index (AI) shows remarkable good correlations during daytime and relatively good correlations over the land.

• 한국항공우주학회지
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• 제37권8호
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• pp.798-804
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• 2009

(주)쎄트렉아이는 400kg 급 지구관측 위성의 주 탑재체로 사용될 고해상도 전자광학카메라, EOS-C 시스템을 개발 중이다. 이 시스템은 DubaiSat-1 위성의 주 탑재체 개발을 통해 획득한 경험을 토대로 보다 향상된 광기계 및 열적 성능을 갖도록 설계되었다. 민감한 광학부품의 운용상 성능을 유지하기 위해 히터를 이용한 능동 열제어 방식이 적용되었고, 이와 더불어 히터 소모 전력을 최소화하기 위해 열 코팅 및 다층박막단열재(MLI)를 사용한 수동 열제어 방식이 적용되었다. 열해석 모델을 이용해 임무궤도에 대한 열해석을 수행하였으며, 해석 결과를 바탕으로 이 시스템의 열제어계가 설계 요구조건을 만족하는 것을 확인하였다.

• 천문학회지
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• 제56권1호
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• pp.59-73
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• 2023

The second generation of stars in the globular clusters (GCs) of the Milky Way (MW) exhibit unusually high N, Na, or Al, compared to typical Galactic halo stars at similar metallicities. The halo field stars enhanced with such elements are believed to have originated in disrupted GCs or escaped from existing GCs. We identify such stars in the metallicity range -3.0 < [Fe/H] < 0.0 from a sample of ~36,800 giant stars observed in the Sloan Digital Sky Survey and Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey, and present their dynamical properties. The N-rich population (NRP) and N-normal population (NNP) among our giant sample do not exhibit similarities in either in their metallicity distribution function (MDF) or dynamical properties. We find that, even though the MDF of the NRP looks similar to that of the MW's GCs in the range of [Fe/H] < -1.0, our analysis of the dynamical properties does not indicate similarities between them in the same metallicity range, implying that the escaped members from existing GCs may account for a small fraction of our N-rich stars, or the orbits of the present GCs have been altered by the dynamical friction of the MW. We also find a significant increase in the fraction of N-rich stars in the halo field in the very metal-poor (VMP; [Fe/H] < -2.0) regime, comprising up to ~20% of the fraction of the N-rich stars below [Fe/H] = -2.5, hinting that partially or fully destroyed VMP GCs may have in some degree contributed to the Galactic halo. A more detailed dynamical analysis of the NRP reveals that our sample of N-rich stars do not share a single common origin. Although a substantial fraction of the N-rich stars seem to originate from the GCs formed in situ, more than 60% of them are not associated with those of typical Galactic populations, but probably have extragalactic origins associated with Gaia Sausage/Enceladus, Sequoia, and Sagittarius dwarf galaxies, as well as with presently unrecognized progenitors.

• 대한원격탐사학회지
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• 제36권2_2호
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• pp.309-323
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• 2020

원격탐사를 이용한 연안 해역의 클로로필 농도 추정은 대부분 다분광 위성 영상 분석을 통해 수행되어 오고 있다. 최근에는 초분광 영상을 활용한 다양한 연구가 시도되고 있으며, 특히 항공기 기반 초분광 영상은 높은 공간 해상도로 좁은 밴드 폭을 가진 수백 개의 밴드로 구성되어 기존의 다분광 위성 영상을 통한 클로로필 추정보다 연안 해역에서 매우 효과적일 수 있다. 본 연구에서는 연안 해역의 클로로필 농도 추정을 위해 초분광 및 위성 기반 클로로필 영상을 비교 검증을 수행하였다. 한반도 남해안에서 수행된 현장조사로 획득된 클로로필 농도 자료와 해수 스펙트럼 자료를 분석한 결과, 높은 클로로필 농도를 갖는 해수 스펙트럼은 570 nm와 680 nm 파장대역 부근에서 peak를 보였다. 이러한 스펙트럼 특징을 활용하여 클로로필 농도 추정을 위한 새로운 밴드비(570 / 490 nm)가 제시되었고, 밴드비와 현장 클로로필 농도 간의 회귀 분석을 통해 새로운 클로로필 경험식이 생성되었다. 현장 클로로필 농도와의 검증 결과, R²의 0.70, RMSE와 mean bias가 각각 2.43와 3.46 mg m^-3으로 유효한 결과를 보였다. 새로운 경험식을 초분광 영상과 위성 영상에 적용한 결과, 초분광 클로로필 영상과 현장 클로로필 간의 평균 RMSE는 0.12 mg m^-3로 위성 클로로필 영상에서 보다 더 높은 정확도로 클로로필 농도 추정 가능하였다. 이 결과를 통하여 초분광 영상을 활용하여 보다 높은 정확도로 연안 해역 클로로필 농도의 고해상도 공간 분포 정보 제공이 가능할 것으로 기대된다.

• 한국농공학회논문집
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• 제62권1호
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• pp.83-93
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• 2020

East Asia, which includes China, Japan, Korea, and Mongolia, is highly impacted by hydroclimate extremes such drought, flood, and typhoon recent year. In 2017, more than 18.5 million hectares of crops have been damaged in China, and Korea has suffered economic losses as a result of severe drought. Satellite-derived rainfall products are becoming more accurate as space and time resolution become increasingly higher, and provide an alternative means of estimating ground-based rainfall. In this study, we verified the availability of rainfall products by comparing widely used satellite images such as Climate Hazards Groups InfraRed Precipitation with Station (CHIRPS), Global Precipitation Climatology Centre (GPCC), and Precipitation Estimation From Remotely Sensed Information Using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR) with ground stations in East Asia. Also, the satellite-based rainfall products were used to calculate the Standardized Precipitation Index (SPI). The temporal resolution is based on monthly images and compared with the past 30 years data from 1989 to 2018. The comparison between rainfall data based on each satellite image products and the data from weather station-based weather data was shown by the coefficient of determination and showed more than 0.9. Each satellite-based rainfall data was used for each grid and applied to East Asia and South Korea. As a result of SPI analysis, the RMSE values of CHIRPS were 0.57, 0.53 and 0.47, and the MAE values of 0.46, 0.43 and 0.37 were better than other satellite products. This satellite-derived rainfall estimates offers important advantages in terms of spatial coverage, timeliness and cost efficiency compared to analysis for drought assessment with ground stations.

• 지구물리와물리탐사
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• 제13권4호
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• pp.336-348
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• 2010

한-중 해저터널 후보지로 선정된 대천-원산도 지역의 부지조사를 위해 버블펄서(Bubble pulser) 음원을 이용한 단일채널 탄성파 탐사와 시추조사가 2008년 및 2009년에 수행되었다. 본 연구는 이 단일채널 탐사자료를 정밀 처리하고 시추자료와 연계하여 후보지역의 해저터널 안정성 평가와 시공설계에 필요한 기반암 심도 및 특성을 분석하는데 목적이 있다. 이를 위해 일반적으로 다중채널 탄성파자료에 적용되던 자료처리 기법 중 주파수-파수영역 필터링(F-K filtering)을 적용하여 교류전원잡음 등을 제거하고, 중합후 심도구조보정(post-stack depth migration) 기법을 적용하여 심도단면을 제작하였다. 수행 결과 단일채널 탄성파자료로부터 향상된 심도영역단면을 제작할 수 있음을 확인하였고, 시추자료와 통합 해석을 통하여 조사지역의 개략적인 기반암 분포와 지질특성을 파악할 수 있었다. 단층, 파쇄대 등의 세밀한 구조 파악은 버블펄서 음원과 단일채널 자료의 특성상 어려웠으나, 좀 더 해상도가 높은 탄성파자료가 있을 시 가능할 것으로 보인다. 이에 향후 해저터널 탐사 시 고해상자료를 얻기 위한 추천사항을 수록하였다.

• Steel and Composite Structures
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• 제36권4호
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• pp.417-426
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• 2020

Drilling processes in fiber-reinforced polymer composites are essential for the assembly and fabrication of composite structural parts. The economic impact of rejecting the drilled part is significant considering the associated loss when it reaches the assembly stage. Therefore, this article tends to illustrate the effect of cutting conditions (feed and speed), and laminate thickness on thrust force, torque, and delamination in drilling woven E-glass fiber reinforced epoxy (GFRE) composites. Four feeds (0.025, 0.05, 0.1, and 0.2 mm/r) and three speeds (400, 800, and 1600 RPM) are exploited to drill square specimens of 36.6×36.6 mm, by using CNC machine model "Deckel Maho DMG DMC 1035 V, ecoline". The composite laminates with thicknesses of 2.6 mm, 5.3 mm, and 7.7 mm are constructed respectively from 8, 16, and 24 glass fiber layers with a fiber volume fraction of about 40%. The drilled specimen is scanned using a high-resolution flatbed color scanner, then, the image is analyzed using CorelDraw software to evaluate the delamination factor. Multi-variable regression analysis is performed to present the significant coefficients and contribution of each variable on the thrust force and delamination. Results illustrate that the drilling parameters and laminate thickness have significant effects on thrust force, torque, and delamination factor.

• 대한전기학회논문지:전력기술부문A
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• 제54권7호
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• pp.328-336
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• 2005

Power quality has become concern both utilities and their customers with wide spread use of electronic and power electronic equipment. The poor quality of electric power causes malfunctions, instabilities and shorter lifetime of the load. In power system operation, power system disturbances such as faults, overvoltage, capacitor switching transients, harmonic distortion and impulses affects power quality. For diagnosing power quality problem, the causes of the disturbances should be understood before appropriate actions can be taken. In this paper we present a new approach to detect, localize, and investigate the feasibility of classifying various types of power quality disturbances. This paper deals with the use of a multi-resolution analysis by a discrete wavelet transform to detect power system disturbances such as interruption, sag, swell, transients, etc. We also proposed do-noising and threshold technique to detect power system disturbances in a noisy environment. To find the better mother wavelet for detecting disturbances, we compared the performance of the disturbance detection with the several mother wavelets such as Daubechies, Symlets, Coiflets and Biorthogonals wavelets. In our analysis, we adopt db4 wavelet as mother wavelet because it shows better results for detecting several disturbances than other mother wavelets. To show the effectiveness of the proposed method, a various case studies are simulated for the example system which is constructed by using PSCAD/EMTDC. From the simulation results. proposed method detects time Points of the start and end time of the disturbances.