• Journal of Astronomy and Space Sciences
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• 제39권4호
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• pp.159-167
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• 2022

Because of the small number of spacecraft available in the Earth's magnetosphere at any given time, it is not possible to obtain direct measurements of the fundamental quantities, such as the magnetic field and plasma density, with a spatial coverage necessary for studying, global magnetospheric phenomena. In such cases, empirical as well as physics-based models are proven to be extremely valuable. This requires not only having high fidelity and high accuracy models, but also knowing the weakness and strength of such models. In this study, we assess the accuracy of the widely used Tsyganenko magnetic field models, T96, T01, and T04, by comparing the calculated magnetic field with the ones measured in-situ by the GOES satellites during geomagnetically disturbed times. We first set the baseline accuracy of the models from a data-model comparison during the intervals of geomagnetically quiet times. During quiet times, we find that all three models exhibit a systematic error of about 10% in the magnetic field magnitude, while the error in the field vector direction is on average less than 1%. We then assess the model accuracy by a data-model comparison during twelve geomagnetic storm events. We find that the errors in both the magnitude and the direction are well maintained at the quiet-time level throughout the storm phase, except during the main phase of the storms in which the largest error can reach 15% on average, and exceed well over 70% in the worst case. Interestingly, the largest error occurs not at the Dst minimum but 2-3 hours before the minimum. Finally, the T96 model has consistently underperformed compared to the other models, likely due to the lack of computation for the effects of ring current. However, the T96 and T01 models are accurate enough for most of the time except for highly disturbed periods.

• 헤리티지:역사와 과학
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• 제41권1호
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• pp.21-33
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• 2008

충청지역의 다양한 유적의 소토(燒土)에서 구한 34점의 고고지자기 측정데이터를 통해 충청지역의 고고지자기 변동 양상을 살펴보고, 더 나아가 국내에서의 지자기의 지역적인 차이에 대해 검토해 보았다. 충청지역의 고고지자기 측정데이터는 거리상으로 차이가 있는 일본의 고고지자기 변동과의 비교에서 보면, 전체적인 변동 모습은 비슷하나 A.D. 300년경에서는 편각이 동쪽으로 10도 이상 치우치는 현저한 차이를 보이고, 그 이외 시기에서는 복각이 다소 깊어지고 편각이 서쪽으로 약간씩 치우치는 지자기의 지역적인 차이가 확인되었다. 이러한 양상은 우리나라 전체의 고고지자기 변동 양상과 큰 차이가 없으며, 충청지역 데이터와의 직접 비교에서도 국내에서는 서력기원전시기와 기원후 시기 모두 뚜렷한 지자기의 지역차는 확인되지 않았다. 앞으로 더 많은 고고지자기 측정 데이터가 증가하고 다양한 시기의 데이터가 채워지면 더욱 명확해 지겠지만, 충청지역 유적의 고고지자기 측정결과를 통해 볼 때, 지자기의 지역적인 차이에 의해 발생하는 고고지자기 측정연대의 오차와 같은 문제점은 우리나라 내에서는 크게 걱정하지 않아도 될 듯하다. 게다가 시료의 채취와 측정에서 신뢰가 가능한 측정데이터를 구하기 위하여 많은 노력들을 하고 있기 때문에, 고고지자기 측정결과에서 추정연대의 오차문제 뿐만 아니라 데이터의 신뢰도의 측면에서도 문제가 없을 것이라 생각된다.

• 한국차세대컴퓨팅학회논문지
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• 제15권3호
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• pp.25-30
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• 2019

지자기 벡터는 센서가 바라보고 있는 방향에 따라 그 값이 달라지는 특성이 있다. 본 논문에서는 그런 문제를 최소화하여 지자기 기반 실내 위치 추정에 사용될 수 있도록 지자기 벡터 보정법을 제안한다. 지자기 기반 실내 위치 추정에서 사용되는 핑거프린팅 기법은 자기장 지도와 현재 위치에서의 자기장 값을 매칭하여 위치를 추정해낸다. 이때, 자기장 센서는 사용자의 이동 방향에 따라 읽어 들이는 자기장 벡터 값이 달라지기 때문에 위치 추정 정확도가 낮아진다. 이를 해결하기 위해 많은 연구들은 자기장 벡터 크기를 사용하지만, 이는 지문의 고유성을 감소시킨다. 따라서 본 논문에서는 지문의 고유성을 유지할 수 있는 자기장 벡터를 그대로 사용하되, 벡터 크기처럼 사용자의 이동방향에 영향을 받지 않도록 벡터 값을 보정하는 방법을 제안한다. 임의의 방향으로 걸어본 결과, 본 연구에서 제안된 보정법을 사용하면 자기장 지도와의 매칭 정확도가 높아지는 것을 확인하였다.

• 천문학회보
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• 제30권1호
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• pp.64.2-64.2
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• 2005

• 전자공학회논문지
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• 제53권7호
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• pp.95-102
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• 2016

쿼드로터의 헤딩 방향 감지를 위하여 일반적으로 활용하는 지자기 센서에서는 주변 자기 간섭 및 롤/피치 축 기울기로 인한 오차가 발생한다. 본 논문에서는 쿼드로터 헤딩 방향 제어를 위하여 지자기 센서와 자이로 센서의 측정 결과를 융합하는 방위각 측정 방법을 제안한다. 롤/피치 축 방향 회전으로 인하여 발생하는 지자기 센서의 좌표축 변화를 분석하고, 수평 자세 제어를 목적으로 측정된 롤/피치 축 각도를 활용하여 지자기 센서의 기울기 보상을 적용한다. 또한, 요 축 각도 측정에 상보필터를 활용하여 지자기 센서의 요 축 각도와 자이로스코프 센서의 요 축 방향 각속도 데이터를 융합한다. 제안한 방식을 실험에 적용하고 결과를 제시하여 요 축 각도 측정의 타당성 및 효과를 검증한다.

• 천문학논총
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• 제15권spc2호
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• pp.1-13
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• 2000

Through the coupling between the near-earth space environment and the polar ionosphere via geomagnetic field lines, the variations occurred in the magnetosphere are transferred to the polar region. According to recent studies, however, the polar ionosphere reacts not only passively to such variations, but also plays active roles in modifying the near-earth space environment. So the study of the polar ionosphere in terms of geomagnetic disturbance becomes one of the major elements in space weather research. Although it is an indirect method, ground magnetic disturbance data can be used in estimating the ionospheric current distribution. By employing a realistic ionospheric conductivity model, it is further possible to obtain the distributions of electric potential, field-aligned current, Joule heating rate and energy injection rate associated with precipitating auroral particles and their energy spectra in a global scale with a high time resolution. Considering that the ground magnetic disturbances are recorded simultaneously over the entire polar region wherever magnetic station is located, we are able to separate temporal disturbances from spatial ones. On the other hand, satellite measurements are indispensible in the space weather research, since they provide us with in situ measurements. Unfortunately it is not easy to separate temporal variations from spatial ones specifically measured by a single satellite. To demonstrate the usefulness of ground magnetic disturbance data in space weather research, various ionospheric quantities are calculated through the KRM method, one of the magneto gram inversion methods. In particular, we attempt to show how these quantities depend on the ionospheric conductivity model employed.

• 천문학회보
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• 제38권2호
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• pp.33-33
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• 2013

We are developing empirical space weather (solar flare, solar proton event, and geomagnetic storm) forecast models based on solar data. In this talk we will review our main results and recent progress. First, we have examined solar flare (R) occurrence probability depending on sunspot McIntosh classification, its area, and its area change. We find that sunspot area and its increase (a proxy of flux emergence) greatly enhance solar flare occurrence rates for several sunspot classes. Second, a solar proton event (S) forecast model depending on flare parameters (flare strength, duration, and longitude) as well as CME parameters (speed and angular width) has been developed. We find that solar proton event probability strongly depends on these parameters and CME speed is well correlated with solar proton flux for disk events. Third, we have developed an empirical storm (G) forecast model to predict probability and strength of a storm using halo CME - Dst storm data. For this we use storm probability maps depending on CME parameters such as speed, location, and earthward direction. We are also looking for geoeffective CME parameters such as cone model parameters and magnetic field orientation. We find that all superstorms (less than -200 nT) occurred in the western hemisphere with southward field orientations. We have a plan to set up a storm forecast method with a three-stage approach, which will make a prediction within four hours after the solar coronagraph data become available. We expect that this study will enable us to forecast the onset and strength of a geomagnetic storm a few days in advance using only CME parameters and the WSA-ENLIL model. Finally, we discuss several ongoing works for space weather applications.

• Journal of Magnetics
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• 제9권3호
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• pp.69-74
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• 2004

A method of processing signals of unaligned geomagnetic sensors placed on the seabed is presented. The offset drifts of the fluxgate sensors are processed by polynomial fitting and the orientations of the sensor axes are found by minimizing the noise power using wavelet analysis. The noise power was reduced by 9.1 dB by processing the components of magnetic field separately using subtraction filter, polynomial fitting and wavelet analysis.

• 천문학회보
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• 제36권2호
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• pp.81.2-81.2
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• 2011

Motivated by recent attempts to derive geomagnetic activity from hourly mean data in long term studies, we test the recursive Kalman filter method to obtain the regular solar variation curve of the geomagnetic field. Using a simple algorithm, we are able to assign a quiet day curve to every day separately, without the need for additional input parameter(s) to define the geomagnetically quiet days. We derive a digital counterpart AhK of the analog range index Ak at the subauroral Sodankyl$\ddot{a}$ station and compare it to the earlier digital estimate Ah and the local Ak index. We find that the new method outperforms the former estimate in every aspect studied and provides a robust, straightforward manner of estimating and verifying the manually scaled Ak index, based on readily available hourly values. The model is independent of sampling; thus, for shorter term studies where high-sampling data are available, more accurate estimates can also be obtained when needed. Therefore, in contrast to other recent approaches, we do not provide a method to quantify irregular activity directly but derive the actual quiet day curves in the traditional manner. In future applications the same algorithm may be used to define a wide variety of geomagnetic indices (such as Ak, Dst, or AE).

• 자원환경지질
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• 제12권2호
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• pp.95-104
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• 1979

The position of any point on the earth's surface can be. represented in the spherical coordinates by surface spherical harmonics. Since geomagnetic field is a function of position on the earth, it can be also expressed by spherical harmonic analysis as spherical harmonics of trigonometric series of $a_m({\theta})$ cos $m{\phi}$ and $b_m({\theta})$ sin $m{\phi}$. Coefficients of surface spherical harmonics, $a_m({\theta})$ and $b_m({\theta})$, can be drawn from the components of the geomagnetic field, declination and inclination, and vice versa. In this paper, components of geomagnetic field, declination and inclination in the Korean peninsula are obtained by spherical harmonic analysis using the Gauss coefficients calculated from the world-wide magnetic charts of 1960. These components correspond to the values of normal geomagnetic field having no disturbances of subsurface mass, structure, and so on. The vertical and total components offer the zero level for the interpretation of geomagnetic data obtained by magnetic measurement in the Korean peninsula. Using this zero level, magnetic anomaly map is obtained from the data of airborne magnetic. prospecting carried out during 1958 to 1960. The conclusions of this study are as follows; (1) The intensity of horizontal component of normal geomagnetic field in Korean peninsula ranges from $2{\times}10^4$ gammas to $2.45{\times}10^4$ gammas. It decreases about 500 with the increment of $1^{\circ}$ in latitude. Along the same. latitude, it increases 250 gammas with the increment of $1^{\circ}$ in longitude. (2) Intensity of vertical component ranges from $3.85{\times}10^4$ gammas to $5.15{\times}10^4$ gammas. It increases. about 1000 gammas with the increment of $1^{\circ}$ in latitude. Along the same latitude, it decreases. 150~240 gammas with the increment of $1^{\circ}$ in longitude. Decreasing rate is considerably larger in higher latitude than in lower latitude. (3) Total intensity ranges from $4.55{\times}10^4$ gammas to $5.15{\times}10^4$ gammas. It increases 600~700 gammas with the increament of $1^{\circ}$ in latitude. Along the same latitude, it decreases 10~90 gammas. with the increment of $1^{\circ}$ in longitude. Decreasing rate is considerably larger in higher latitude as the case of vertical component. (4) The declination ranges from $-3.8^{\circ}$ to $-11.5^{\circ}$. It increases $0.6^{\circ}$ with the increment of $1^{\circ}$ in latitude. Along the same latutude, it increases $0.6^{\circ}$ with the increment of l O in longitude. Unlike the cases of vertical and total component, the rate of change is considerably larger in lower latitude than in higher latitude. (5) The inclination ranges from $57.8^{\circ}$ to $66.8^{\circ}$. It increases about $1^{\circ}$ with 'the increment of $1^{\circ}$ in latitude Along the same latitude, it dereases $0.4^{\circ}$ with the increment of $1^{\circ}$ in longitude. (6) The Boundaries of 5 anomaly zones classified on the basis of the trend and shape of anomaly curves correspond to the geologic boundaries. (7) The trend of anomaly curves in each anomaly zone is closely related to the geologic structure developed in the corresponding zone. That is, it relates to the fault in the 3rd zone, the intrusion. of granite in the 1st and 5th zones, and mountains in the 2nd and 4th zones.