• 태양에너지
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• 제13권2_3호
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• pp.79-90
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• 1993

본 연구에서는 다공성 물질을 이용한 공기용 태양열 집열기(Solar Air Heater)의 설계를 위한 이론적 해석을 하였다. 해석시 필요한 유리 덮개 및 다공성 매질의 파장에 따른 복사특성을 Visible Spectrometer 및 FT-IR로 측정하였다. 다공성 매질로 15 메쉬의 Stainless Steel Wire Screen을 대상으로 하였다. 열전달 현상은 1차원으로 가정하고, 열복사는 Two-Flux Model을 사용하여, 여러 경우의 유량 및 복사 물성치에 대한 집열기 내부에서의 공기온도 및 다공성 매질의 온도를 계산하여 이에 따른 집열기의 효율 등을 계산하였다. 결과로는 무광택 페인트 코팅이 된 경우가 좋은 복사특성을 보였고, 공기유량이 증가할수록, 알베도(Albedo)는 가시광선 영역에서는 작을수록, 적외선 영역에서는 클수록 집열기의 효율은 증가하였다. 다공성 매질의 두께는 0.001m가 적합함을 보였다. 본 연구에서 이는 광학적 두께(Optical Thickness)가 약 1 정도를 의미한다.

• 대기
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• 제22권1호
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• pp.117-128
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• 2012

Does snow depth initialization have a quantitative impact on sub-seasonal to seasonal prediction skill? To answer this question, a snow depth initialization technique for seasonal forecast system has been implemented and the impact of the initialization on the seasonal forecast of surface air temperature during the wintertime is examined. Since the snow depth observation can not be directly used in the model simulation due to the large systematic bias and much smaller model variability, an anomaly rescaling method to the snow depth initialization is applied. Snow depth in the model is initialized by adding a rescaled snow depth observation anomaly to the model snow depth climatology. A suite of seasonal forecast is performed for each year in recent 12 years (1999-2010) with and without the snow depth initialization to evaluate the performance of the developed technique. The results show that the seasonal forecast of surface air temperature over East Asian region sensitively depends on the initial snow depth anomaly over the region. However, the sensitivity shows large differences for different timing of the initialization and forecast lead time. Especially, the snow depth anomaly initialized in the late winter (Mar. 1) is the most effective in modulating the surface air temperature anomaly after one month. The real predictability gained by the snow depth initialization is also examined from the comparison with observation. The gain of the real predictability is generally small except for the forecasting experiment in the early winter (Nov. 1), which shows some skillful forecasts. Implications of these results and future directions for further development are discussed.

• 대기
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• 제27권4호
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• pp.423-433
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• 2017

The spatial and temporal variations in radiative forcing (RF) and mean temperature changes of greenhouse gases (GHGs), such as $CO_2$, $CH_4$, and $N_2O$, were analyzed at urban center (Yeon-dong) and background sites (Gosan) on Jeju Island during 2010~2015, based on a modeling approach (i.e., radiative transfer model). Overall, the RFs and mean temperature changes of $CO_2$ at Yeon-dong during most years (except for 2014) were estimated to be higher than those at Gosan. This might be possibly because of its higher concentrations at Yeon-dong due to relatively large energy consumption and small photosynthesis and also the difference in radiation flux due to the different input condition (e.g., local time and geographic coordinates of solar zenith angle) in the model. The annual mean RFs and temperature changes of $CO_2$ were highest in 2015 ($2.41Wm^{-2}$ and 1.76 K) at Yeon-dong and in 2013 ($2.22Wm^{-2}$ and 1.62 K) at Gosan (except for 2010 and 2011). The maximum monthly/seasonal mean RFs and temperature changes of $CO_2$ occurred in spring (Mar. and/or Apr.) or winter (Jan. and/or Feb.) at the two sites during the study period, whereas the minimum RFs and temperature changes in summer (Jun.-Aug.). In the case of $CH_4$ and $N_2O$, their impacts on the RF and mean temperature changes were very small (an order of magnitude lower) compared to $CO_2$. The spatio-temporal differences in these RF values of GHGs might primarily depend on the atmospheric profile (e.g., ozone profile), surface albedo, local time (or solar zenith angle), as well as their mass concentrations.

• 대한원격탐사학회지
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• 제32권2호
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• pp.97-104
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• 2016

본 연구에서는 일본 오사카에서 AERONET 선포토미터로 관측된 데이터를 분석하여 440, 675, 870, 1020 nm 파장에서의 입자 편광소멸도를 산출하였다. 산출된 결과는 같은 지역에서 측정된 라이다 자료로부터 얻어진 532 nm에서의 입자 편광소멸도와 비교하였다. 두 값은 440 nm를 제외하고는 잘 일치되는 결과를 보였고, 상관계수($R^2$)는 440, 675, 870, 1020 nm에서 각각 0.28, 0.81, 0.88 0.89의 값을 보였다. 가장 높은 상관계수를 보인 1020 nm에서의 입자 편광소멸도를 기준으로 값의 변화에 따른 입자의 혼합정도를 확인하였을 때, 순수 황사의 경우 높은 편광소멸도를 보이고 오염입자가 혼합될수록 값이 낮아짐을 보였다. 이는 단산란 알베도와 입자 크기 분포를 통하여 확인하였다.

• 대한원격탐사학회지
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• 제29권2호
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• pp.243-251
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• 2013

본 연구는 인공위성과 지상 원격탐사 자료를 이용하여 동북아 지역에서 발생하는 황사현상의 중장거리 이동에 따른 광학적 특성 변화를 분석하였다. 동북아시아 지역의 Aerosol Robotic Network(AERONET)의 선포토미터 관측 지점 중에 황사의 발원지로 Dunhuang과 Inner-Mongolia, 발원지에 근접한 풍하측 지점으로 Yulin과 Beijing, 그리고 장거리 이동 지점으로 한국의 Anmyon과 Gosan, 일본의 Noto, 이렇게 7곳을 선정하여 자료를 분석하였다. 황사의 발생 및 이동 경로를 파악하기 위하여 자외선 원격탐사 기법을 사용하는 인공위성인 Ozone Monitoring Instrument(OMI) 관측자료를 활용하였다. 발원지에서의 단산란알베도는 440 nm에서 0.90에서 0.96 사이의 값으로 높았으나 풍하측이나 장거리 이동 지역에서는 그 값이 감소하였다. 또한, 파장에 따른 단산란알베도 값의 차이는 발원지에서는 높게 나타났으나 이동된 지역에서는 그 차이가 감소하였다. 이러한 장거리 이동에 따른 황사의 광흡수 특성의 변화는 이동 중 탄소입자와 같은 대기 오염물질과의 혼합으로부터 기인하는 것으로 판단된다.

• 대한원격탐사학회지
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• 제33권4호
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• pp.359-375
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• 2017

We developed fog detection algorithm (KNU_FDA) based on the optical and textural properties of fog using satellite (COMS) and ground observation data. The optical properties are dual channel difference (DCD: BT3.7 - BT11) and albedo, and the textural properties are normalized local standard deviation of IR1 and visible channels. Temperature difference between air temperature and BT11 is applied to discriminate the fog from other clouds. Fog detection is performed according to the solar zenith angle of pixel because of the different availability of satellite data: day, night and dawn/dusk. Post-processing is also performed to increase the probability of detection (POD), in particular, at the edge of main fog area. The fog probability is calculated by the weighted sum of threshold tests. The initial threshold and weighting values are optimized using sensitivity tests for the varying threshold values using receiver operating characteristic analysis. The validation results with ground visibility data for the validation cases showed that the performance of KNU_FDA show relatively consistent detection skills but it clearly depends on the fog types and time of day. The average POD and FAR (False Alarm Ratio) for the training and validation cases are ranged from 0.76 to 0.90 and from 0.41 to 0.63, respectively. In general, the performance is relatively good for the fog without high cloud and strong fog but that is significantly decreased for the weak fog. In order to improve the detection skills and stability, optimization of threshold and weighting values are needed through the various training cases.

• 한국지하수토양환경학회지:지하수토양환경
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• 제20권5호
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• pp.16-25
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• 2015

The City of Boulder is located at an average elevation of 1,655 m (5,430 feet), the foothills of the Rocky Mountains in Colorado. Its daily air temperature is much varying and snow is very frequent and heavy even in spring. This paper examines characteristics of shallow (surface and depth = 10 cm) soil temperatures measured from January to May 2015 in the high elevation city Boulder, Colorado. The surface soil temperature quickly responded to the air temperature with the strongest periodicity of 1 day while the subsurface soil temperatures showed a less correlation and delayed response with that. The short-time Fourier of the soil temperatures uncovered their very low frequencies characteristics in heavy snow days while it revealed high frequencies of their variations in warm spring season. The daily minimum air temperature exhibited high cross-correlations with the soil temperatures without lags unlike the maximum air temperature, which is derived from its higher and longer auto-correlation and stronger spectrums of low frequencies than the maximum air temperature. The snow depth showed an inverse relationship with the soil temperature variations due to snow's low thermal conductivity and high albedo. Multiple regression for the soil temperatures using the air temperature and snow depth presented its predicting possibility of them even though the multiple r² of the regression is not that much satisfactory (r² = 0.35-0.64).

• 항공우주시스템공학회지
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• 제14권1호
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• pp.36-43
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• 2020

위성 열 설계의 시작은 운용궤도의 열 환경 분석을 통한 최악의 운용 환경을 예측하는 것이다. 위성은 주어진 임무에 맞는 다양한 형태의 운용궤도를 가지기 때문에 노출되는 열 환경 또한 다르다. 따라서, 위성의 궤도조건을 고려한 외부 열 환경 분석이 필수이며, 이를 통해 선정된 위성의 최악의 조건에 대해 열적 안정성을 보장하는 설계를 수행하게 된다. 궤도 열 환경 분석을 위해서는 궤도역학은 물론 우주 열 환경과 위성체 사이의 열 교환 관계에 대한 이해가 필요하다. 이에 본 논문에서는 지구궤도 내 우주 열 환경에 관한 기초자료를 제공하고, 위성체에 유입되는 우주 열 유입량을 계산하는 열 관계식을 서술함으로써 궤도 열 환경 분석의 이해를 돕고자 하였다. 또한, 가상의 위성 예제를 통해 임무기간 중 궤도 열 환경을 분석하는 전반적인 과정을 보였다.

• 한국태양에너지학회 논문집
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• 제31권3호
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• pp.133-144
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• 2011

The objective of this study is to analyze the characteristic of radiation environment in the urban and rural through the field observation in the summer. The radiation balance was compared through the measurement of the shortwave radiation and long-wave radiation in the urban, sub-urban, and rural. The following conclusion could be obtained from this research. (1)In the results of observation including the rain-day, it was found that the short wave radiance in the urban is lower about 10% than the rural. (2)The upper part of atmosphere layers in the urban are aabsorb much short wave radiation energies compared with the rural relatively. It can increase the temperature of the upper part of atmosphere layers and the emittance of long wave radiation. (3)The ratio of the downward short wave radiation to the downward long wave radiation was 1.24 for the urban, 1.28 for sub-urban and 1.35 for rural. It can be estimated that the atmosphere condition of the rural is better than that of other areas. (4)The net radiation of the rural was lower that of the urban. It was found that the energy in and outflow of the rural is easier than that of the urban. (5)The temperature variation for the long-wave radiation change of the rural showed more sensitive than that of the urban. It was came from the radiation characteristics of the surrounding environment and can be used as the important index to evaluate the thermal environment characteristic of urban.

• 천문학회보
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• 제41권2호
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• pp.48.3-49
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• 2016

We have five different types of observation modes with regard to the Deep Ecliptic Patrol of the Southern Sky (DEEP-South); Opposition Census (OC) for targeted photometry, Sweet Spot Survey (S1) for discovery and orbit characterization of Atens and Atiras, Ecliptic Survey (S2) for asteroid family studies and comet census, NEOWISE follow-up (NW) for near simultaneous albedo measurements in the visible bands, and Target of Opportunity (TO) observation for follow-up either for unpredictable events or targets of special interests. Different exposures with such different modes result in a wide range of background noise level, the number of background stars and the mover's projected speed in each image. The Moving Object Detection Program (MODP) utilizes multiple mosaic images being taken for the same target fields at different epochs at the three KMTNet sites. MODP employs existing software packages such as SExtractor (Source-Extractor) and SCAMP (Software for Calibrating Astrometry and Photometry); SExtractor generates object catalogs, while SCAMP conducts precision astrometric calibration, then MODP determines if a point source is moving. This package creates animated stamp images for visual inspection with MPC reports, the latter for checking whether an object is known or unknown. We evaluate the astrometric accuracy and efficiency of MODP using the year one dataset obtained from DEEP-South operations.