• 한국지구과학회지
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• 제30권3호
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• pp.344-353
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• 2009

광해의 정도를 알아보기 위해 서울대 사범대학 주변 밤하늘의 밝기를 측정하였다. 표준성을 이용하여 고도에 따른 소광 계수 및 영점 상수를 구한 결과, 2009년 1월 28일에는 소광계수가 $k_B$=0.359, 영점상수는 $C_B$=4.397이 었고, 2009년 3월 27일에는 소광계수가 $k_B$=0.896, $k_V$=0.725, 영점상수는 $C_B$=6.235, $C_V$=6.027이었다. 밤하늘의 밝기는 동, 서, 남, 북 네 방위에 대해 고도 $20^{\circ}$, $40^{\circ}$, $60^{\circ}$, $75^{\circ}$, $90^{\circ}$에서 측정하였다. IRAF를 사용하여 전처리하고 측광한 결과, 1월 28일의 시상은 평균 5.1"였고 3월 27일은 5.7"이었다. 밤하늘의 등급은 방위 및 고도에 따라 $16{\leq}m_V$, $m_B{\leq}18$이었다. 도심 방향의 밤하늘 밝기는 어두운 지역에 비해 2-4정도 밝게 나타났다. 이러한 관측 조건에서 구경 40cm인 망원경을 통해 육안으로 관측할 수 있는 한계 등급은 밤하늘의 밝기 정도에 따라 대략 11-13등급이다. 1월과 3월의 밤하늘 밝기를 비교해 본 결과, B필터에서 1월이 3월에 비해 1등급 정도 어두운 것으로 나타났다.

• 천문학논총
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• 제11권1호
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• pp.177-196
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• 1996

We have investigated the astronomical observational environments at the Choejung-san GEODSS site which is located at the south of Taegu, Korea. As a part of the investigation, seeing and night sky brightness were measured outside nearby the GEODSS site using the Celestron 8-inch portable reflector with $192{\times}165$ pixels Lynxx CCD camera during the period of December 1994 to April 1996. The average seeing values of 4.8 arcsecond in B filter and 5.1 arcsecond in V filter were determined using the IRAF software. These values might be overestimated and would be reduced by at least 1 arc second in both filters if they were measured by more stable telescope system with solid mount and under a dome. We also compare the average seeing value at the GEODSS site with those at three other observatories, the Bohyunsan Optical Astronomy Observatory, the Sobaeksan Optical Astronomy Observatory, and the Seoul National University Observatory, for justification of the above guess. Unfortunately the night sky brightness measurement was not successful mainly due to the short exposure time. The utilizing plan of the GEOSS site is discussed based on the average seeing value, naked-eye sky brightness measurement, analysis of the existing thirty-year weather data and twenty-year urban planning of the metropolitan Taegu city for the year of 2016.

• 한국지구과학회지
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• 제40권5호
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• pp.464-475
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• 2019

대부분의 중 고등학교가 도심지에 위치하며 사용할 수 있는 천문 관측 장비에 제한이 있다는 점을 고려하여 DSLR 카메라와 교육용 소형 망원경을 결합하여 도심지 밤하늘 밝기를 측정하였다. DSLR 카메라의 다양한 설정은 ISO 설정 외에는 원본 파일에 영향을 주지 않았으며, 필터 변환까지 고려한 일반적인 측광 정밀도는 대략 0.1 등급이다. 밤하늘 밝기는 천정 부근의 경우 B, V, r 필터에서 각각 약 17.5, 17.1, $16.9mag\;arcsec^{-2}$으로 측정되었다. 이를 통해 도심지의 대략적인 한계등급은 B 필터에서 17.5 등급, V와 r 필터에서 17등급으로 추정할 수 있다. 관측지점과 가까운 대규모 인공 조명은 고도와 필터에 무관하게 밤하늘 밝기를 약 $0.6mag\;arcsec^{-2}$ 증가시킴으로써 관측 환경을 악화시키는 주요인으로 나타났다.

• 천문학회보
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• 제25권2호
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• pp.82-82
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• 2000

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2000년도 한국우주과학회보 제9권2호
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• pp.82-82
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• 2000

No Abstract, See Full Text

• 천문학회지
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• 제35권1호
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• pp.41-57
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• 2002

We have written a code called QDM_sca, which numerically solves the problem of radiative transfer in an anisotropically scattering, spherical atmosphere. First we formulate the problem as a second order differential equation of a quasi-diffusion type. We then apply a three-point finite differencing to the resulting differential equation and transform it to a tri-diagonal system of simultaneous linear equations. After boundary conditions are implemented in the tri-diagonal system, the QDM_sca radiative code fixes the field of specific intensity at every point in the atmosphere. As an application example, we used the code to calculate the brightness of atmospheric diffuse light(ADL) as a function of zenith distance, which plays a pivotal role in reducing the zodiacal light brightness from night sky observations. On the basis of this ADL calculation, frequent uses of effective extinction optical depth have been fully justified in correcting the atmospheric extinction for such extended sources as zodiacal light, integrated starlight and diffuse galactic light. The code will be available on request.

• 한국지구과학회지
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• 제26권2호
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• pp.149-159
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• 2005

Simultaneous observations of MODIS (Moderate-resolution Imaging Spectroradiometer) onboard the Aqua and Terra satellites and weather station at ground near the Inchon International Airport (37.2-37.7 N, 125.7-127.2 E) during the period from December 2002 to September 2004 have been utilized in order to analyze the characteristics of satellite-observed infrared (IR) and visible data under fog and clear-sky conditions, respectively. The differences $(T_{3.7-11})$ in brightness temperature between $3.75{\mu}m\;and\;11.0{\mu}m$ were used as threshold values for remote-sensing fog (or low clouds) from satellite during day and night. The $T_{3.7-11}$ value during daytime was greater by about 21 K when it was foggy than that when it was clear, but during nighttime fog it was less by 1.5 K than during nighttime clear-sky. The value was changed due to different values of emission of fog particles at the wavelength. Since the near-IR channel at $3.7{\mu}m$ was affected by solar and IR radiations in the daytime, both IR and visible channels (or reflectance) have been used to detect fog. The reflectance during fog was higher by 0.05-0.6 than that during clear-sky, and varied seasonally. In this study, the threshold values included uncertainties when clouds existed above a layer of fog.

• 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.

• 천문학회보
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• 제40권1호
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• pp.88.2-88.2
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• 2015

지난 2009-2010년 수행한 제 1차 수도권 밤하늘 밝기 측정에 이어, 우리는 2014년 12월부터 2015년 2월까지 제 2차 수도권 밤하늘 밝기 측정을 수행하였다. 이번 2차 측정에서는 지난 1차 측정과 가능한 한 동일한 장소와 조건에서 밤하늘 밝기를 측정함으로써, 지난 5년간 발생한 밤하늘 밝기 및 주변 환경의 변화와 이 둘 사이의 상관관계를 알아보고자 하였다. 밤하늘 밝기 측정에 사용된 기기는 1차 측정과 마찬가지로 'SQM(Sky Quality Meter)-L'을 사용하였다. SQM-L은 표면등급($mag/arcsec^2$) 단위로 밤하늘을 측정하며 측정 오차는 ${\pm}0.1$ 등급이다. 이번 측정 결과 밤하늘 밝기가 가장 어두운 지역은 경기도 가평군 청평면 고성리(20.6 등급)로, 1차 측정에서의 가장 어두운 지역과 동일했다. 반면 가장 밝은 지역은 서울 영등포구 윤중초교와 서울 중구 남산초교(16.5 등급)로 나타났으며, 가장 어두운 지역과 밝은 지역 사이의 밤하늘 밝기 차이는 약 40배(~4 등급)로 나타났다. 이번에 측정한 밤하늘 밝기는 지난 1차 관측에 비해 전 지역에서 평균 0.5 등급 어두워진 것으로 나타났다. 특히 서울 은평구 갈현초교는 5년 사이에 1.5 등급 어두지면서 가장 큰 차이를 보였다(1차: 16.0 등급, 2차: 17.5 등급). 본 포스터에서는 이번 측정 결과와 진행 과정을 소개하고 두 관측 기간 사이에 발생한 밤하늘 밝기 변화의 원인에 대하여 토론하고자 한다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
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• pp.664-667
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• 2006

Seasonal threshold values for fog detection over the ten airport areas in the Korean Peninsula have been derived, using the satellite-observed data of polar-orbit (Aqua/Terra MODIS) and geostationary (GOES-9) during two years. The values are obtained from reflectance at 0.65 ${\mu}m$ $(R_{0.65})$ and the difference in brightness temperature between 3.7 ${\mu}m$ and 11 ${\mu}m$ $(T_{3.7-11})$. In order to examine the discrepancy between the threshold values of two kinds of satellites, the following parameters have been analyzed under the condition of daytime/nighttime and fog/clear-sky, utilizing their simultaneous observations over the Seoul Metropolitan Area. The parameters are the brightness temperature at 3.7 ${\mu}m$ $(T_{3.7})$, the temperature at 11 ${\mu}m$ $(T_{11})$, and $T_{3.7-11}$ for day and night. The $R_{0.65}$ data are additionally included in the daytime. The GOES-9 thresholds over the nine airport areas except the Cheongju airport have revealed the accuracy of 60% in the daytime and 70% in the nighttime, based on statistical verification as follows; FAR, POD and CSI. However, the accuracy decreases in the foggy cases with twilight, precipitation, short persistence, or the higher cloud above fog.