• 제목/요약/키워드: mid-latitude

검색결과 120건 처리시간 0.024초

MODTRAN 모델을 이용한 다목적 실용위성 2호 MSC의 입사복사량 계산

  • 김용승;강치호
    • 항공우주기술
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    • 제1권1호
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    • pp.173-176
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    • 2002
  • 본 연구에서는 대기복사모델인 MODTRAN를 이용해 다목적실용위성 2호 탑재체인 Multispectral Camera (MSC)의 입사복사량에 대한 계산을 수행하고 그 결과를 분석해 본다. 모델계산은 4 계절 조건을 모의실험하기 위해 1월 15일, 4월 15일, 7월 15일과 10월 15일에 대해 중위도 동절기 및 하절기, 그리고 US 표준대기를 사용했다. 다목적실용위성 2호 궤도 조건과 각 계절에 대한 대표적인 태양천정각 (solar zenith angle)을 이용하였다. 시정거리는 대류권 에어로솔 소광계수 (tropospheric aerosol extinction)에 해당하는 50 km를 사용하고 지표의 알비도는 맑은 날 지구 연평균 값에 해당하는 0.135가 사용되었다. MSC 계약서 값은 위 일반적 조건을 가정하고 얻은 모델 계산 총복사량보다 MSC 관측 파장대역 대부분에서 상당히 크다는 것을 알게 되었다. 이들 결과로부터 향후 획득될 MSC영상은 비교적 어두운 영상이 될 것으로 추론 되며 이에 대한 대책이 검토되고 수립되어야 하겠다.

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Robustness Examination of Tracking Performance in the Presence of Ionospheric Scintillation Using Software GPS/SBAS Receiver

  • Kondo, Shun-Ichiro;Kubo, Nobuaki;Yasuda, Akio
    • 한국항해항만학회:학술대회논문집
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    • 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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    • pp.235-240
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    • 2006
  • Ionospheric scintillation induces a rapid change in the amplitude and phase of radio wave signals. This is due to irregularities of electron density in the F-region of the ionosphere. It reduces the accuracy of both pseudorange and carrier phase measurements in GPS/satellite based Augmentation system (SBAS) receivers, and can cause loss of lock on the satellite signal. Scintillation is not as strong at mid-latitude regions such that positioning is not affected as much. Severe effects of scintillation occur mainly in a band approximately 20 degrees on either side of the magnetic equator and sometimes in the polar and auroral regions. Most scintillation occurs for a few hours after sunset during the peak years of the solar cycle. This paper focuses on estimation of the effects of ionospheric scintillation on GPS and SBAS signals using a software receiver. Software receivers have the advantage of flexibility over conventional receivers in examining performance. PC based receivers are especially effective in studying errors such as multipath and ionospheric scintillation. This is because it is possible to analyze IF signal data stored in host PC by the various processing algorithms. A L1 C/A software GPS receiver was developed consisting of a RF front-end module and a signal processing program on the PC. The RF front-end module consists of a down converter and a general purpose device for acquiring data. The signal processing program written in MATLAB implements signal acquisition, tracking, and pseudorange measurements. The receiver achieves standalone positioning with accuracy between 5 and 10 meters in 2drms. Typical phase locked loop (PLL) designs of GPS/SBAS receivers enable them to handle moderate amounts of scintillation. So the effects of ionospheric scintillation was estimated on the performance of GPS L1 C/A and SBAS receivers in terms of degradation of PLL accuracy considering the effect of various noise sources such as thermal noise jitter, ionospheric phase jitter and dynamic stress error.

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Unusual Enhancements of NmF2 in Anyang Ionosonde Data

  • Yun, Jongyeon;Kim, Yong Ha;Kim, Eojin;Kwak, Young-Sil;Hong, Sunhak
    • Journal of Astronomy and Space Sciences
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    • 제30권4호
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    • pp.223-230
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    • 2013
  • Sudden enhancements of daytime NmF2 appeared in Anyang ionosonde data during summer seasons in 2006-2007. In order to investigate the causes of this unusual enhancement, we compared Anyang NmF2's with the total electron contents (GPS TECs) observed at Daejeon, and also with ionosonde data at at mid-latitude stations. First, we found no similar increase in Daejeon GPS TEC when the sudden enhancements of Anyang NmF2 occurred. Second, we investigated NmF2's observed at other ionosonde stations that use the same ionosonde model and auto-scaling program as the Anyang ionosonde. We found similar enhancements of NmF2 at these ionosonde stations. Moreover, the analysis of ionograms from Athens and Rome showed that there were sporadic-E layers with high electron density during the enhancements in NmF2. The auto-scaling program (ARTIST 4.5) used seems to recognize sporadic-E layer echoes as a F2 layer trace, resulting in the erroneous critical frequency of F2 layer (foF2). Other versions of the ARTIST scaling program also seem to produce similar erroneous results. Therefore we conclude that the sudden enhancements of NmF2 in Anyang data were due to the misrecognition of sporadic-E echoes as a F-layer by the auto-scaling program. We also noticed that although the scaling program flagged confidence level (C-level) of an ionogram as uncertain when a sporadic-E layer occurs, it still automatically computed erroneous foF2's. Therefore one should check the confidence level before using long term ionosonde data that were produced by an auto-scaling program.

다목적실용위성 2호 MSC 총복사량의 모델 계산 (Model Calculation of Total Radiances for KOMPSAT-2 MSC)

  • 김용승;강치호
    • 대한원격탐사학회지
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    • 제17권3호
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    • pp.211-218
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    • 2001
  • 대기복사모델인 MODTRAN을 이용해 다목적실용위성 2호 탑재체인 Multispectral Camera (MSC)의 총복사량에 대한 계산을 수행하고 그 결과를 분석해 보았다. 모델 계산에서 4계절 조건을 모의실험하기 위해 1월 15일, 7월 15일 계산에 대해 중위도 동절기 및 하절기 모델대기를, 4월 15일, 10월 15일에 대해 US 표준대기를 각각 사용했다. 다목적실용위성 2호 궤도 조건과 각 계절에 대한 대표적인 태양천정각 (solar zenith angle)이 고려되었다. 시정거리는 대류권 에어로솔 소광계수 (tropospheric aerosol extinction)에 해당하는 50km가, 지표의 알베도는 맑은 날 지구 연평균 값에 해당하는 0.135가 가정되었다. MSC 계약서 값은 위 일반적 조건을 가정하고 얻은 모델 계산 총복사량보다 MSC 관측 파장대역 대부분에서 상당히 크다는 것을 알게 되었다. 또한 균일한 지표 알베도를 가정하고 얻은 모델 결과의 분광파장 특징이 MSC 계약서 값의 경향과 다름을 보였다. 이들 결과로부터 향후 획득될 MSC영상은 비교적 어두운 영상이 될 것으로 추론된다.

Curves on the Mother and Indices of the Rete Carved to Ryu Geum's Astrolabe

  • Mihn, Byeong-Hee;Kim, Sang Hyuk;Nam, Kyoung Uk;Lee, Ki-Won;Jeong, Seong Hee
    • 천문학회보
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    • 제43권2호
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    • pp.48.4-49
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    • 2018
  • We studyed an Korean astrolabe made by Ryu Geum (1741~1788), the late Joseon Confucian scholar. It has a diameter of 17 cm and a thickness of 6 mm and is now owned by Museum of Silhak. In the 1267 of the reign of Kublai Khan of Mogol Empire, Jamal al Din, an Ilkhanate astronomer, present an astrolabe to his emperor together with 6 astronomical instruments. In 1525, an astrolabe was first made in Korea by Lee, Sun (李純, ?~?), a Korean astronomer and royal official of Joseon Dynasty. He was referred to Gexiang xinshu, a Mongloian-Chinese book by Zhao, Youqin (1280-1345), an astronomer of Mongolian Empire. This astrolabe has not been left. In the mid-17th century, an astrolabe was introduced to Joseon again through Hungai tongxian tushuo (渾蓋 通憲圖設) edited by Chinese Mathematician Li Zhi-zao (李之藻, 1565~1630), that originated from Astrolabium (1593) of Christoph Clavius (1538-1612). It seems that Ryu refered to Hungai tongxian tushuo which affect to Hongae-tongheon-ui (渾蓋通憲儀) edited by Nam, Byeong-Cheol (南秉哲, 1817~1863). We analysis lots of circles on the mother and a set of index from the rete of of Ryu's astrolabe. We find that the accuracy of circles has about 0.2~0.4 mm in average if the latitude of this astrolabe is 38 degrees. 11 indices of the rete point bright stars of the northern and southern celestial hemisphere. Their tip's accuracies are about $2^{\circ}.9{\pm}3^{\circ}.2$ and $2^{\circ}.3{\pm}2^{\circ}.8$ on right ascension and declination of stars respectively.

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기상청 기후예측시스템(GloSea6) 과거기후 예측장의 앙상블 확대와 초기시간 변화에 따른 예측 특성 분석 (Assessment of the Prediction Derived from Larger Ensemble Size and Different Initial Dates in GloSea6 Hindcast)

  • 김지영;박연희;지희숙;현유경;이조한
    • 대기
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    • 제32권4호
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    • pp.367-379
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    • 2022
  • In this paper, the evaluation of the performance of Korea Meteorological Administratio (KMA) Global Seasonal forecasting system version 6 (GloSea6) is presented by assessing the effects of larger ensemble size and carrying out the test using different initial conditions for hindcast in sub-seasonal to seasonal scales. The number of ensemble members increases from 3 to 7. The Ratio of Predictable Components (RPC) approaches the appropriate signal magnitude with increase of ensemble size. The improvement of annual variability is shown for all basic variables mainly in mid-high latitude. Over the East Asia region, there are enhancements especially in 500 hPa geopotential height and 850 hPa wind fields. It reveals possibility to improve the performance of East Asian monsoon. Also, the reliability tends to become better as the ensemble size increases in summer than winter. To assess the effects of using different initial conditions, the area-mean values of normalized bias and correlation coefficients are compared for each basic variable for hindcast according to the four initial dates. The results have better performance when the initial date closest to the forecasting time is used in summer. On the seasonal scale, it is better to use four initial dates, where the maximum size of the ensemble increases to 672, mainly in winter. As the use of larger ensemble size, therefore, it is most efficient to use two initial dates for 60-days prediction and four initial dates for 6-months prediction, similar to the current Time-Lagged ensemble method.

Impacts of Aerosol Loading on Surface Precipitation from Deep Convective Systems over North Central Mongolia

  • Lkhamjav, Jambajamts;Lee, Hyunho;Jeon, Ye-Lim;Seo, Jaemyeong Mango;Baik, Jong-Jin
    • Asia-Pacific Journal of Atmospheric Sciences
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    • 제54권4호
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    • pp.587-598
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    • 2018
  • The impacts of aerosol loading on surface precipitation from mid-latitude deep convective systems are examined using a bin microphysics model. For this, a precipitation case over north central Mongolia, which is a high-altitude inland region, on 21 August 2014 is simulated with aerosol number concentrations of 150, 300, 600, 1200, 2400, and $4800cm^{-3}$. The surface precipitation amount slightly decreases with increasing aerosol number concentration in the range of $150-600cm^{-3}$, while it notably increases in the range of $600-4800cm^{-3}$ (22% increase with eightfold aerosol loading). We attempt to explain why the surface precipitation amount increases with increasing aerosol number concentration in the range of $600-4800cm^{-3}$. A higher aerosol number concentration results in more drops of small sizes. More drops of small sizes grow through condensation while being transported upward and some of them freeze, thus increasing the mass content of ice crystals. The increased ice crystal mass content leads to an increase in the mass content of small-sized snow particles largely through deposition, and the increased mass content of small-sized snow particles leads to an increase in the mass content of large-sized snow particles largely through riming. In addition, more drops of small sizes increase the mass content of supercooled drops, which also leads to an increase in the mass content of large-sized snow particles through riming. The increased mass content of large-sized snow particles resulting from these pathways contributes to a larger surface precipitation amount through melting and collision-coalescence.

CE-QUAL-W2를 이용한 성층 저수지에서 CO2의 시공간적 분포 및 물질수지 분석 (Characterizing Spatiotemporal Variations and Mass Balance of CO2 in a Stratified Reservoir using CE-QUAL-W2)

  • 박형석;정세웅
    • 한국물환경학회지
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    • 제36권6호
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    • pp.508-520
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    • 2020
  • Dam reservoirs have been reported to contribute significantly to global carbon emissions, but unlike natural lakes, there is considerable uncertainty in calculating carbon emissions due to the complex of emission pathways. In particular, the method of calculating carbon dioxide (CO2) net atmospheric flux (NAF) based on a simple gas exchange theory from sporadic data has limitations in explaining the spatiotemporal variations in the CO2 flux in stratified reservoirs. This study was aimed to analyze the spatial and temporal CO2 distribution and mass balance in Daecheong Reservoir, located in the mid-latitude monsoon climate zone, by applying a two-dimensional hydrodynamic and water quality model (CE-QUAL-W2). Simulation results showed that the Daecheong Reservoir is a heterotrophic system in which CO2 is supersaturated as a whole and releases CO2 to the atmosphere. Spatially, CO2 emissions were greater in the lacustrine zone than in the riverine and transition zones. In terms of time, CO2 emissions changed dynamically according to the temporal stratification structure of the reservoir and temporal variations of algae biomass. CO2 emissions were greater at night than during the day and were seasonally greatest in winter. The CO2 NAF calculated by the CE-QUAL-W2 model and the gas exchange theory showed a similar range, but there was a difference in the point of occurrence of the peak value. The findings provide useful information to improve the quantification of CO2 emissions from reservoirs. In order to reduce the uncertainty in the estimation of reservoir carbon emissions, more precise monitoring in time and space is required.

한반도 지상 풍속의 장기 추세 추정: 관측 자료의 물리적 및 통계적 보정 (Long-Term Trend of Surface Wind Speed in Korea: Physical and Statistical Homogenizations)

  • 최영주;박창현;손석우;김혜진
    • 대기
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    • 제31권5호
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    • pp.553-562
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    • 2021
  • The long-term trend of surface wind speed in Korea is estimated by correcting wind measurements at 29 KMA weather stations from 1985 to 2019 with physical and statistical homogenization. The anemometer height changes at each station are first adjusted by applying physical homogenization using the power-law wind profile. The statistical homogenization is then applied to the adjusted data. A standard normal homogeneity test (SNHT) is particularly utilized. Approximately 40% of inhomogeneities detected by the SNHT match with the sea-level-height change of each station, indicating that an SNHT is an effective technique for reconciling data inhomogeneity. The long-term trends are compared with homogenized data. Statistically significant negative trends are observed along the coast, while insignificant trends are dominant inland. The mean trend, averaged over all stations, is -0.03 ± 0.07 m s-1 decade-1. This insignificant trend is due to a trend change across 2001. A decreasing trend of -0.10 m s-1 decade-1 reverses to an increasing trend of 0.03 m s-1 decade-1 from 2001. This trend change is consistent with mid-latitude wind change in the Northern hemisphere, indicating that the long-term trend of surface wind speed in Korea is partly determined by large-scale atmospheric circulation.

Construction of a Spatio-Temporal Dataset for Deep Learning-Based Precipitation Nowcasting

  • Kim, Wonsu;Jang, Dongmin;Park, Sung Won;Yang, MyungSeok
    • Journal of Information Science Theory and Practice
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    • 제10권spc호
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    • pp.135-142
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    • 2022
  • Recently, with the development of data processing technology and the increase of computational power, methods to solving social problems using Artificial Intelligence (AI) are in the spotlight, and AI technologies are replacing and supplementing existing traditional methods in various fields. Meanwhile in Korea, heavy rain is one of the representative factors of natural disasters that cause enormous economic damage and casualties every year. Accurate prediction of heavy rainfall over the Korean peninsula is very difficult due to its geographical features, located between the Eurasian continent and the Pacific Ocean at mid-latitude, and the influence of the summer monsoon. In order to deal with such problems, the Korea Meteorological Administration operates various state-of-the-art observation equipment and a newly developed global atmospheric model system. Nevertheless, for precipitation nowcasting, the use of a separate system based on the extrapolation method is required due to the intrinsic characteristics associated with the operation of numerical weather prediction models. The predictability of existing precipitation nowcasting is reliable in the early stage of forecasting but decreases sharply as forecast lead time increases. At this point, AI technologies to deal with spatio-temporal features of data are expected to greatly contribute to overcoming the limitations of existing precipitation nowcasting systems. Thus, in this project the dataset required to develop, train, and verify deep learning-based precipitation nowcasting models has been constructed in a regularized form. The dataset not only provides various variables obtained from multiple sources, but also coincides with each other in spatio-temporal specifications.