• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.22.2-22.2
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• 2011

이 연구에서는 한반도 상공의 전리층 총전자수를 격자 형태로 나타냈다. 이를 위해 국토해양부 GPS 상시관측소에서 제공 중인 코드와 위상 측정값을 선형조합하였으며 그 결과물을 이용하여 시선방향 총전자수를 산출하였다. 이때 전리층 총전자수 산출결과의 정확도를 향상시키기 위해 가중최소자승법을 이용하여 위성과 수신기의 하드웨어 오차인 DCB(Differencial Code Bias)를 추정하였으며 추정된 DCB값은 IGS에서 제공 중인 DCB값과 비교하여 정확도를 확인하였다. 산출된 시선방향 총전자수를 연직방향 총전자수로 변환하기 위해 사상함수를 적용하였으며, 이를 다시 각 격자점에서의 연직방향 총전자수로 변환하기 위해 기존 연직방향 총전자수에 역거리 가중 보간법을 적용하였다. 각 격자점에서의 총전자수는 IGS(International GNSS Service)에서 제공 중인 GIM(Global Ionosphere Map) 모델의 총전자수와 비교하여 정확도를 확인하였다. 산출된 총전자수는 2시간 간격으로 나타내어 한반도 상공 전리층 총전자수의 변화 경향을 확인하였다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.3
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• pp.293-301
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• 2011

The ionospheric delay is the largest error source in GPS positioning after the SA effect has been turned off in May, 2000. In this study, we used 44 permanent GPS stations being operated by National Geographic Information Institute (NGII) to estimate Total Electron Content (TEC) based on pseudorange measurements phase-leveled by a linear combination with carrier phases. The Differential Code Bias (DCB) of GPS satellites and receivers was estimated and applied for an accurate estimation of the TEC. To validate our estimates of DCB, changes of TEC values after DCB application were investigated. As a result, the RMS error went down by about an order of magnitude; from 35~45 to 3~4 TECU. After the DCB correction, ionospheric TEC maps were produced at a spatial resolution of $1^{\circ}{\times}1^{\circ}$. To analyze the effect of the number of sites used for map generation on the accuracy of TEC values, we tried 10, 20, 30, and 44 stations and the RMS error was computed with the Global Ionosphere Map as the truth. While the RMS error was 5.3 TECU when 10 sites are used, the error reduced to 3.9 TECU for the case of 44 stations.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.35.2-35.2
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• 2010

전리층의 총전자수는 이중주파수 GPS 관측정보에 의해 추정될 수 있다. 그러나 GPS 신호에 의해 추정된 총전자수 값은 'DCB(Differential Code Biases)'라 불리는 GPS 위성과 수신기의 하드웨어 바어어스에 의해 영향을 받는다. 이러한 하드웨어 바이어스는 전리층 총전자수 추정의 정확도에 심각한 영향을 줄 수 있기 때문에 반드시 고려해야만 한다. 수신기의 하드웨어 바이어스는 수십 나노초(nano-seconds)에 도달할 수 있고, 수신기의 타입 또는 주변 온도 그리고 수신기 모델마다 다를 수 있다. 이 연구에서는 한국천문연구연과 국토해양부에서 운영하는 GPS 기준국 관측정보를 활용하여 각각의 수신기 바이어스를 1시간 간격으로 추정하고, 변화 특성을 분석한다. 일부 GPS 수신기 바이어스는 IGS (International GNSS Service)에서 제공하는 수신기 바이어스와 그 결과를 비교하여 검증한다. 또한 한반도 상공의 전리층 총전자수 추정과 GPS 수신기 바이어스의 영향을 제시한다.

• Journal of Astronomy and Space Sciences
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• v.24 no.4
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• pp.269-274
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• 2007

We established a regional ionospheric model for investigating ionospheric TEC (Total Electron Contents) variations over the Korean Peninsula during major geomagnetic storms. In order to monitor the ionospheric TEC variations, we used nine permanent GPS reference stations uniformly distributed in South Korea operated by the Korea Astronomy and Space Science Institute (KASI). The cubic spline smoothing (CSS) interpolation method was used to analyze the characteristics of the ionospheric TEC variations. It has been found that variations of TEC over the Korean Peninsula increase when a major geomagnetic storm occurred on November 20, 2003. The TEC has increased about one and a half of those averaged quite days at the specific time during a geomagnetic storm. It has been indicated that the KASI GPS-derived TEC has a correlation with the geomagnetic storm indices (eq. Kp and Dst indices).

• Journal of Astronomy and Space Sciences
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• v.11 no.1
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• pp.71-80
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• 1994

It is generally known that the measurement of the ionospheric total electron content(TEC) by GPS can more accurately monitor the broader area of the ionosphere than other current methods. \Ve measured the TEC along a slant path considering the arrival time differences of P-code which is transmitted from GPS satellites with the modulation on two L-band carrier frequencies, L1 (1574.42MHz) and L2 (1227.60MHz). Under the assumptions that the ionosphere is uniformly distributed and its average height is 350km, we transformed the slant TEC to the vertical TEC at the point that the line-of-sight direction to GPS satellite cut across the average height of the ionosphere. Because there is no dual frequency P-code GPS receiver in Korea, we used the data observed at the TAIW GPS station ($N25^{\circ},E121.5^{\circ}$) in Taiwan which is one of the core stations in International GPS and Geodynamics Services (IGS). The TEC values obtained in this work showed a typical daily variation of the ionosphere which is high in the daytime and low in the nighttime. Our results are found to be consistent with the SOLAR-DAILY data of NOAA and the Klobuchar's model for the ionospheric correction of GPS. In addition, in the cornparision with SOLAR-DAILY data, we estimated the precision of our TEC measurement as 2 TEC.

• Bulletin of the Korean Space Science Society
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• 1994.04a
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• pp.9-9
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• 1994

• Bulletin of the Korean Space Science Society
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• 2004.04a
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• pp.43-43
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• 2004

국제적인 시각비교를 위해 GPS를 이용하고 있으나, GPS 신호에는 위성까지의 거리정보뿐 아니라 위성시계, 대류층, 이온층, 다중경로 오차 등이 포함되어 있다. 그 중 이온층 지연시간을 측정하기 위해서는 Ll과 L2 반송파 신호로부터 얻어지는 P코드와 위상정보를 이용할 수 있다. 반송파 위상 정보는 P코드보다 해상도가 좋기 때문에 위상정보를 이용하게 되면 고정밀도의 이온층 지연시간을 얻게 된다. 이온층 지연시간을 통해 총전자수를 나타내는 TEC 값을 얻을 수 있는데, 관측지점으로부터 시간에 따라 가장 높은 고도의 위성을 선택하여 P코드와 반송파 위상 정보를 통한 이온층 총전자수를 파악하고 정밀도를 비교분석 하였다. (중략)

• Journal of Astronomy and Space Sciences
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• v.16 no.2
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• pp.285-292
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• 1999

To determine a geographical position by GPS signal, the effect of the ionosphere must be considered to improve accuracy. This has led us to continuously try to find the TEC of the ionosphere by using the GPS signal. So far the way to find TEC has been developed and the information obtained from this can be used not only to increase the accuracy of determining the position, but also to study the ionosphere. In this research, the TEC MAP over Korea was obtained by using the data collected from eight GPS stations around the Far East Asia, which is the common way to represent TEC over some regional or global region.

• Bulletin of the Korean Space Science Society
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• 2007.04a
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• pp.69-69
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• 2007

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.24 no.2
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• pp.167-173
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• 2006

Ionosphere is the largest error source on propagation of GPS signals. Dual frequency (L1,L2) GPS receiver can be effectively able to eliminate the ionosphere error by using linear combination of two frequencies, but the single frequency receiver (L1) have to compute the ionosphere error. In this research, we developed the new ionospheric model with $1^{\circ}$ by $1^{\circ}$ spatial resolution based on the grid from using 9 GPS reference stations which have been operated by KASI (Korea Astronomy and Space Science Institute) and computed TEC (Total Electron Contents) over South Korea by epoch. This paper gives the positioning results of Klobuchar model with that of a newly developed KASI regional ionospheric model and shows the positioning precision of the KASI regional ionospheric model along with TEC variation of ionosphere.