• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.9 no.1
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• pp.27-35
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• 1991

The total station which is able to measure angles and distances simultaneously, and G.P.S., 3-dimensional satellite surveying system will be employed as important equipments for establishing and re-adjusting large geodetic networks. The objective of this study is to suggest possibilities of application of combination adjustment by means of studying characteristics of networks adjusted according to detection gross errors included in angles and distances by least square method. It is expected that the results of this study were used for determination of national geodetic networks but also large or small construction site.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.30 no.4
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• pp.413-422
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• 2012

After development of GPS in the 1960's, the United States released SA(Selective Availability) in 2000 and then the GPS has become commercialized to the present. The result of repeatedly developed GPS observation, the GPS real-time observation methods is RTK which basically always needs two base stations and has a fault of the accuracy decreasing as the distance between a mobile station and a receiver is increasing. Because of these weakness, VRS method has come out. VRS(Virtual Reference Station) generates the imaginary point near mobile station from several observatory datum of GPS, sets the accurate location of mobile station, thus shows high reliability and mobility. Now, the cadastral datum point is used with azimuth, repetition, and graphical traversing method for traverse network. The result of measurement indicates many problems because of different accomplishment interval given point, restrictions on the length of the conductor, many errors on the observations. So, this study did comparative analysis of the cadastral datum points through VRS method by Continuously Operating Reference Station. Through the above comparative analysis, The comparative result between surveyed result with repetition method through total station observed Cadastral Control Points and surveyed result with VRS-RTK has shown that average error of x-axis is -0.08m, average error of y-axis, +0.07m and average distance error is +0.11m.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.208-208
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• 2023

북한강 유역은 대한민국을 대표하는 한강의 제1지류로 상류에 북한산이 위치하여 풍부한 자연환경과 생태계를 보유하고 있다. 해당 유역은 수력 및 다목적댐이 위치하여 수력발전과 수도권 물공급에 있어 중요한 역할을 하고 있다. 더욱이, 상수원보호구역으로 지정되어 있어 수질오염 예방을 위한 수질 관리가 필요하다. 기존 연구의 경우 북한강 유역 내 1개 다목적댐(소양강댐) 지점에 대한 수량 및 수질 매개변수 검·보정을 수행한 사례가 있으나 다목적댐 및 수력댐을 모두 고려한 사례는 없어 관련 연구가 요구되는 실정이다. 본 연구에서는 SWAT 모형을 활용한 북한강 유역 내 수량·수질을 분석 및 평가하고자 한다. 대상유역은 북한강 유역이며 저류를 하지 않는 평화의 댐을 제외한 5개 댐(화천댐, 춘천댐, 소양강댐, 의암댐, 청평댐)에 대해 모형에서 고려하였다. 자료평가기간은 1983년부터 2021년이며 기상 및 지형자료, 저수지 자료, 점오염원 자료를 입력자료로 활용하였다. Penman/Monteith 방법, SCS 방법, Muskingum 방법, 저수지 운영 방법(일 단위 관측 방류량 입력 및 목표 저수량 유지)을 활용하여 모형 모의를 수행하였다. 매개변수 검·보정은 수량(댐 유입량 및 방류량, 저류량) 및 수질(유사량, 총질소, 총인) 자료를 활용하여 수량 9개 지점과 수질 6개 지점, 댐 저수지 5개 지점을 중심으로 수행하였다. 수량 및 수질에 대한 도시적 및 통계적 평가를 통해 관측 및 모의 간의 정확도를 평가하였다. 평가결과, 수량은 임남댐의 영향을 받는 일부 댐을 제외한 대부분의 댐 유역에서 관측 및 모의 유량 간의 적합도가 우수하게 나타났다. 수질은 수량의 영향을 직접적으로 받아 일부 지점을 제외한 대부분 지점에서 관측 및 모의값 간의 적합도가 높게 나타났다. 검·보정 적절성 판단을 위한 정량적 평가결과, 수량의 경우 결정계수(R²) 0.64~0.94, 용적오차(PBIAS) 0.09%~15.77%로 적정한 것으로 나타났다. 수질의 경우 용적오차 0.00%~29.14% 사이로 적정범위 안에 포함된 것으로 나타났다. 본 연구결과는 기후변화와 연계하여 미래 기간의 수량 및 수질 분석 연구에 기여할 것으로 기대된다.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.1
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• pp.74-81
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• 2001

The sensorless scheme for Switched Reluctance Motor(SRM) drives must have the robustness and reliability because the noise and error are sensitive. These elements make electrically noisy environments due to the proximity of high current power circuits with small signal electronic circuits when SRM drives. Also, due to the leakage inductances and finite coupling capacitances, these can cause the noise on any low voltage current and voltage measurement circuit. The position estimate error occurs because the current and voltage including the noise are sued as the inputs of sensorless algorithm. In this paper the high robustness and resistance of input noise re described. The fuzzy logic based rotor estimation algorithm and the observer model are used to reduce the tolerance of input data.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.25 no.5
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• pp.399-405
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• 2007

Providing a precise positioning information is the primary characteristics of GPS. The relative positioning technique which utilizes the common measurements between a GPS reference station and a user is generally used to do the generation of a precise positioning. But if user is far from a GPS reference site, the properties of medium penetrated by GPS signals will be different from each other, It is difficult to eliminate the error sources such as the ionosphere and the troposphere effectively by the double differencing method. In this study the additional error correction values with the ionosphere and the troposphere to the data processing have applied. As a result, the positioning accuracy of fourteen out of seventeen testing sites were improved by appling the error correction values. We also analysed the improved rate of the positioning accuracy by the baseline.

• Korean Journal of Remote Sensing
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• v.38 no.6_1
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• pp.1125-1139
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• 2022

In an unmanned aerial vehicles (UAVs) system, a physical offset can be existed between the global positioning system/inertial measurement unit (GPS/IMU) sensor and the observation sensor such as a hyperspectral sensor, and a lidar sensor. As a result of the physical offset, a misalignment between each image can be occurred along with a flight direction. In particular, in a case of multi-sensor system, an observation sensor has to be replaced regularly to equip another observation sensor, and then, a high cost should be paid to acquire a calibration parameter. In this study, we establish a precise sensor model equation to apply for a multiple sensor in common and propose an independent physical offset estimation method. The proposed method consists of 3 steps. Firstly, we define an appropriate rotation matrix for our system, and an initial sensor model equation for direct-georeferencing. Next, an observation equation for the physical offset estimation is established by extracting a corresponding point between a ground control point and the observed data from a sensor. Finally, the physical offset is estimated based on the observed data, and the precise sensor model equation is established by applying the estimated parameters to the initial sensor model equation. 4 region's datasets(Jeon-ju, Incheon, Alaska, Norway) with a different latitude, longitude were compared to analyze the effects of the calibration parameter. We confirmed that a misalignment between images were adjusted after applying for the physical offset in the sensor model equation. An absolute position accuracy was analyzed in the Incheon dataset, compared to a ground control point. For the hyperspectral image, root mean square error (RMSE) for X, Y direction was calculated for 0.12 m, and for the point cloud, RMSE was calculated for 0.03 m. Furthermore, a relative position accuracy for a specific point between the adjusted point cloud and the hyperspectral images were also analyzed for 0.07 m, so we confirmed that a precise data mapping is available for an observation without a ground control point through the proposed estimation method, and we also confirmed a possibility of multi-sensor fusion. From this study, we expect that a flexible multi-sensor platform system can be operated through the independent parameter estimation method with an economic cost saving.

• The Journal of the Acoustical Society of Korea
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• v.22 no.3
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• pp.224-232
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• 2003

In this paper, efficient deployment method of sensors and target positioning performance with respect to measurement error are dealt with. Active sonar can be categorized into Monostatic, Bistatic, Multistatic sonar, and characteristics of respective sonar are different. Assuming that each sensor can receive range and angular information, we compare the performance of Monostatic, Bistatic, and Multistatic systems. And we suggest Weighted least square (WLS) which gives the weight to former case, LS. In particular. adopting suggested method we investigate the target positioning performance according to number of sensor, distance from transmitter to receiver, and propose efficient arrangement rule for Multistatic sonar configurations. According to the experimental results, RMSE of Multistatic sonar is found to be superior to Monostatic and Bistatic by 35.98%. 37.45% respectively, and WLS is superior to LS approximately by 7.4% in average. Furthermore, as the difference of respective sensor's variance is large, it is observed that the improvement ratio of target positioning performance is increased.

• Journal of Advanced Navigation Technology
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• v.23 no.3
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• pp.237-244
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• 2019

Since SBAS provides users with GNSS orbit, clock, and ionospheric corrections and integrity, the more precise positioning is possible. As the SBAS service area is expanded due to the development of the SBAS and the installation of the additional ground stations, there is a region where two or more SBAS messages can be received. However, the research on multi-constellation SBAS selection method has not carried out. In this study, we compared the result of positioning accuracy after applying the SBAS correction selected by using WAAS priority, EGNOS priority, or error covariance comparison method to LEO satellites in the regions where WAAS and EGNOS signals are transmitted simultaneously. When using WAAS priority method, 3D orbit error is smallest at 2.57 m. The covariance comparison method is outperform at the center of the overlap region far from each WAAS and EGNOS stations. In the eastern region near the EGNOS stations, the 3D orbit errors using EGNOS priority method is 8% smaller than the errors using the WAAS priority method.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.25.2-25.2
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• 2011

저궤도위성의 정밀궤도결정은 GPS 위성과 수신기의 시계 공통오차를 제거하기 위해 이중 차분하는 방법으로 요구된 위치 정밀도를 충족시켜왔다. 그러나 빠른 속도로 지구를 회전하는 저궤도위성의 정밀궤도결정에 있어 이러한 이중 차분방법은 지구상에 광범위하게 분포된 지상 IGS 망 처리에 많은 계산 부담을 안고 있다. 그리고 지상 측지뿐만 아니라 저궤도위성을 이용한 기상관측 또는 긴급한 영상 처리 응용분야에서도 고정밀도 준실시간(Near Real Time-NRT) 처리가 요구되고 있다. 고정밀 준실시간 정밀궤도결정을 위한 대안은 이중주파수 GPS 수신기으로 IGS에서 제공되는 정밀궤도력을 갖고 고정밀 단독측위가 가능한 정밀단독측위(precise point positioning) 기법으로 상대측위와 버금가는 위치 정밀도를 얻을 수 있다. 다목적실용위성 5호는 고정밀 합성 레이더 영상 처리를 위해서 요구되는 20 cm 위성 위치 정밀도를 만족시키고, 대기 기상관측을 위해 GPS 전파 엄폐 측정값 수집을 목적으로 고정밀 이중주파수 GPS 수신기(Integrated GPS and Occultation Receiver, IGOR)를 탑재하고 있다. 이 논문에서는 IGOR의 이전 제품인 Blackjack 수신기를 탑재한 GRACE 위성의 실제 GPS 데이터를 사용하여 대략 3 ~ 5cm의 위치 정밀도를 얻었다. 준실시간 정밀궤도결정에서 정밀도 손실없이 궤도결정 처리 지연시간(latency)을 줄이는 것이 중요하다. 이 지연시간은 GPS 측정값의 양에 따라 크게 좌우되기에 GPS 측정값 샘플링 주기를 10초에서 640초까지 변화시켜가면서 정밀도를 분석한 결과, 위치 정밀도 손실없이도 궤도결정처리 지연시간을 단축시킬 수 있음을 제시하고 있다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.4
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• pp.461-467
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• 2009

Relative positioning technique by GPS that can obtain the high positioning accuracy has been used for generation of high precision positioning with elimination or the reduction of the common errors. This paper gives some algorithms for RTK and considers the filter to estimate the positioning information and integer ambiguities at each epoch in the whole algorithms. The extended kalman filter has been employed to estimate the state parameters and the modified LAMBDA to resolve the integer ambiguities. The data processing was performed by GPS single frequency and dual frequency in short baseline. The verification procedure of these positioning compared with results from Bernese 5.0 software. We presented some statistic values on positioning errors and the rates of integer ambiguity resolution.