• 대한공간정보학회지
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• 제16권3호
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• pp.117-126
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• 2008

지구중력장모델은 지오이드 모델링에 있어서 기준면을 결정하기 위하여 사용되어 왔으며, 1980년대 이후로 많은 전지구적 지오포텐셜모델이 개발되었다. 오늘날 EGM96과 EIGEN-GL04C 모델이 전세계적으로 가장 많이 사용되어 왔으나 EGM2008이라고 불리우는 지구중력장모델이 미국의 NGA에 의해 올해 개발되었다. 본 연구에서는 이러한 세 개의 지구중력장모델에 대하여 구면조화분석을 실시하고 그 결과를 비교하고자 하였다. 따라서 구면조화분석은 한반도 일원에 대하여 $1'{\times}1'$격자간격으로 EGM96과 EIGEN-GL04C 모델은 최대차수 360으로, EGM2008의 경우 차수를 360, 720, 1440, 2190으로 변화시켜 가면서 실시하였다. 정확도 평가를 위하여 464점의 GPS/leveling 데이터에서 기하학적 지오이드고가 계산되었으며, 평가결과 EGM2008 모델이 EGM96이나 EIGEN-GL04C 모델에 비하여 상당한 수준으로 정확도를 개선시킴을 알 수 있었으며 한반도 일원에서 14cm 이내의 정밀도로, LSC적합 이후에는 5.5cm의 정밀도로 지오이드고를 계산할 수 있음을 알 수 있었다.

• Journal of Astronomy and Space Sciences
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• 제31권1호
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• pp.41-50
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• 2014

The Earth is not perfectly spherical and its rotational axis is not fixed in space, and these geophysical and kinematic irregularities work as dominant perturbations in satellite orbit propagation. The International Earth Rotation Service (IERS) provides the Conventions as guidelines for using the Earth's model and the reference time and coordinate systems defined by the International Astronomical Union (IAU). These guidelines are directly applied to model orbital dynamics of Earth satellites. In the present work, the effects of the latest conventions released in 2010 on orbit propagation are investigated by comparison with cases of applying the previous guidelines, IERS Conventions (2003). All seven major updates are tested, i.e., for the models of the precession/nutation, the geopotential, the ocean tides, the ocean pole tides, the free core nutation, the polar motion, and the solar system ephemeris. The resultant position differences for one week of orbit propagation range from tens of meters for the geopotential model change from EGM96 to EGM2008 to a few mm for the precession/nutation model change from IAU2000 to IAU2006. The along-track differences vary secularly while the cross-track components show periodic variation. However, the radial-track position differences are very small compared with the other components in all cases. These phenomena reflect the variation of the ascending node and the argument of latitude. The reason is that the changed models tested in the current study can be regarded as small fluctuations of the geopotential model from the point of view of orbital dynamics. The ascending node and the argument of latitude are more sensitive to the geopotential than the other elements. This study contributes to understanding of the relation between the Earth's geophysical properties and orbital motion of satellites as well as satellite-based observations.

• Korean Journal of Geomatics
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• 제2권1호
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• pp.7-15
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• 2002

Recent development of ultra-high and high degree Earth geopotential model opens new avenues to determine the Earth gravity field through spectral techniques to a very high accuracy and resolution. However, due to data availability, quality, and type, the performance of these new EGMs needs to be validated in regional or local scale geoid modeling. For establishing the best reference surface of geoid determination, recent geopotential models are evaluated using GPS/Leveling-derived geometric geoid and the Korean gravimetrical GEOID (KGEOID98) developed by National Geography Institute in 1998. Graphical and statistical comparisons are made for EGM96, GFZ97, PGM2000A and GPM98A models. The mean and standard deviation of difference between geometric height and geoid undulation calculated from GFZ97 are $1.9\pm{46.7}\;cm$. It is shown that the GFZ97 and the GPM98A models are better than the others in the Korean peninsula because the GFZ97 has a smaller bias. It means that the KGEOID98 needs some improvement using the GFZ97 instead of EGM96.

• 대기
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• 제28권3호
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• pp.233-245
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• 2018

This study explores the Subseasonal-to-Seasonal (S2S) prediction skills of the Northern Hemisphere mid-latitude geopotential height in the Global Seasonal forecasting model version 5 (GloSea5) hindcast experiment. The prediction skills are quantitatively verified for the period of 1991~2010 by computing the Anomaly Correlation Coefficient (ACC) and Mean Square Skill Score (MSSS). GloSea5 model shows a higher prediction skill in winter than in summer at most levels regardless of verification methods. Quantitatively, the prediction limit diagnosed with ACC skill of 500 hPa geopotential height, averaged over $30^{\circ}N{\sim}90^{\circ}N$, is 11.0 days in winter, but only 9.1 days in summer. These prediction limits are primarily set by the planetary-scale eddy phase errors. The stratospheric prediction skills are typically higher than the tropospheric skills except in the summer upper-stratosphere where prediction skills are substantially lower than upper-troposphere. The lack of the summer upper-stratospheric prediction skill is caused by zonal mean error, perhaps strongly related to model mean bias in the stratosphere.

• 한국측량학회지
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• 제38권2호
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• pp.153-163
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• 2020

After launching the GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) which obtains high-frequency gravity signal using a gravity gradiometer, many research institutes are concentrating on the development of GGM (Global Geopotential Model) based on GOCE data and evaluating its precision. The precision of some GGMs was also evaluated in Korea. However, some studies dealt with GGMs constructed based on initial GOCE data or others applied a part of GNSS (Global Navigation Satellite System) / Leveling data on UCPs (Unified Control Points) for the precision evaluation. Now, GGMs which have a higher degree than EGM2008 (Earth Gravitational Model 2008) are available and UCPs were fully established at the end of 2019. Thus, EIGEN-6C4 (European Improved Gravity Field of the Earth by New techniques - 6C4), GECO (GOCE and EGM2008 Combined model), XGM2016 (Experimental Gravity Field Model 2016), SGG-UGM-1, XGM2019e_2159 were collected with EGM2008, and their precisions were assessed based on the GNSS/Leveling data on UCPs. Among GGMs, it was found that XGM2019e_2159 showed the minimum difference compared to a total of 5,313 points of GNSS/Leveling data. It is about a 1.5cm and 0.6cm level of improvement compare to EGM2008 and EIGEN-6C4. Especially, the local biases in the northern part of Gyeonggi-do, Jeju island shown in the EGM2008 was removed, so that both mean and standard deviation of the difference of XGM2019e_2159 to the GNSS/Leveling are homogeneous regardless of region (mountainous or plain area). NGA (National Geospatial-Intelligence Agency) is currently in progress in developing EGM2020 and XGM2019e_2159 is the experimentally published model of EGM2020. Therefore, it is expected that the improved GGM will be available shortly so that it is necessary to verify the precision of new GGMs consistently.

• 제어로봇시스템학회논문지
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• 제13권10호
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• pp.962-969
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• 2007

In this paper, an approach is developed for relative state estimation of satellite formation flying. To estimate relative states of two satellites, the Extended Kalman Filter Algorithm is adopted with the relative distance and speed between two satellites and attitude of satellite for measurements. Numerical simulations are conducted under two circumstances. The first one presents both chief and deputy satellites are orbiting a circular reference orbit around a perfectly spherical Earth model with no disturbing acceleration, in which the elementary relative orbital motion is taken into account. In reality, however, the Earth is not a perfect sphere, but rather an oblate spheroid, and both satellites are under the effect of $J_2$ geopotential disturbance, which causes the relative distance between two satellites to be on the gradual increase. A near-Earth orbit decays as a result of atmospheric drag. In order to remove the modeling error, the second scenario incorporates the effect of the $J_2$ geopotential force, and the atmospheric drag, and the eccentricity in satellite orbit are also considered.

• 한국지구과학회지
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• 제28권7호
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• pp.936-946
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• 2007

기울어진 자전축을 갖는 회전계에서, 일정한 각속도로 회전하는 동서풍이 있는 경우에 대해서 로스비하우어비츠 파동의 섹터모드(적도에 대한 반구 비대칭의 첫 번째 모드)와 균형을 이루는 지위고도장을 해석적으로 유도하였다. 균형장은 발산방정식으로부터 시간변화를 제거하고 라플라시안 연산자를 역산함으로써 구하였다. 역산은 비선형항의 계산과 포이슨 방정식의 해를 구하는 두 단계의 연산과정으로 이루어져 있다. 두 번째 단계에서, 구면조화함수로 표현되는 강제력의 항은 구면조화함수의 선형관계를 이용하였고, 그 이외의 항은 구면조화함수를 적분함으로써 구하였다. 균형장은 여섯 개의 동서파수 성분으로 표현됨이 드러났다. 본 연구에서 구한 균형장은 적도에 대하여 비대칭의 구조를 가지기 때문에, 대칭의 구조만을 가지는 것에 비하여 미분방정식의 수치해의 검종법으로서의 활용도가 높다. 일정한 각속도를 갖는 배경 동서풍이 지구의 자전각속도와 같거나 1/2에 해당하는 경우에는, 일부 동서파수 성분이 제거되는 것으로 나타났다. 이론적으로 구한 균형장은 정교한 수치모델을 통하여 구한 균형장과 거의 정확하게 같은 것으로 밝혀져, 이론적 해의 타당성이 입증되었다. 마지막으로, 로스비하우어비츠 파동의 섹터모드와 균형을 이루는 지위고도장의 안정성을 장기간시간적분을 통하여 살펴보았다.

• 대기
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• 제30권2호
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• pp.115-124
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• 2020

The Northern Hemisphere extratropical prediction skill of the Korea Meteorological Administration (KMA) Global Data Assimilation and Prediction System (GDAPS) is examined for January 2019. The real-time prediction skill, evaluated with mean squared skill score (MSSS) of 30-90°N geopotential height field at 500 hPa (Z500), is ~8 days in the troposphere. The MSSS of Z500 considerably decreases after 3 days mainly due to the increasing eddy errors. The eddy errors are largely explained by the eddy-phased errors with minor contribution of amplitude errors. In particular, planetary-scale eddy errors are considered as a main reason of rapidly increasing errors. It turns out that such errors are associated with the blocking highs over North Pacific (NP) and Euro-Atlantic (EA) regions. The model overestimates the blocking highs over NP and EA regions in time, showing dependence of blocking predictability on blocking initializations. This result suggests that the extratropical prediction skill could be improved by better representing blocking in the model.

• 대기
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• 제22권4호
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• pp.455-464
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• 2012

This study investigates a 12 month-lead predictability of PNU Coupled General Circulation Model (CGCM) V1.1 hindcast, for which an oceanic data assimilated initialization is used to generate ocean initial condition. The CGCM, a participant model of APEC Climate Center (APCC) long-lead multi-model ensemble system, has been initialized at each and every month and performed 12-month-lead hindcast for each month during 1980 to 2011. The 12-month-lead hindcast consisted of 2-5 ensembles and this study verified the ensemble averaged hindcast. As for the sea-surface temperature concerns, it remained high level of confidence especially over the tropical Pacific and the mid-latitude central Pacific with slight declining of temporal correlation coefficients (TCC) as lead month increased. The CGCM revealed trustworthy ENSO prediction skills in most of hindcasts, in particular. For atmospheric variables, like air temperature, precipitation, and geopotential height at 500hPa, reliable prediction results have been shown during entire lead time in most of domain, particularly over the equatorial region. Though the TCCs of hindcasted precipitation are lower than other variables, a skillful precipitation forecasts is also shown over highly variable regions such as ITCZ. This study also revealed that there are seasonal and regional dependencies on predictability for each variable and lead.

• 환경영향평가
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• 제16권2호
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• pp.157-168
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• 2007

In case there is a need to run the multi-year urban scale air qulaity model, it is a difficult task due to the computational demand, requiring the statistical approach for the long time atmospheric environmental assessment. In an effort to approach toward long term urban assessment, the sixteen synoptic meteorological conditions are statistically classified from the estimated geostrophic wind speeds and directions of 850 hPa geopotential height field during 2000 ~ 2005. The geostrophic wind directions are subdivided into four even intervals (north, east, south, and west), geostrophic wind speeds into two classes(${\leq}5m/s$ and >5m/s), and daily mean cloud amount into 2 classes(${\leq}5/10$ and >5/10), which result into sixteen classes of the synoptic meteorological cases for each season. The frequency distributions for each 16 synoptic meteorological case are examined and some discussions on how these synoptic classifications can be used in the environmental assessment are presented.