• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.3
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• pp.237-247
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• 2011

As of 2011, 72 Permanent GPS Stations are installed to control DGPS reference points by the National Geographic Information Institute in South Korea. As the center of the Earth's mass continues to move, the coordinates of the permanent GPS stations become inconsistent over time. Thus, a reference frame using a set of coordinates and their velocities of a global network of stations at a specific period has been used to solve the inconsistency. However, the relative movement of the permanent GPS stations can lower the accuracy of GPS relative positioning. In this research, we first analyzed the data collected daily during the past 30 months at the 40 permanent GPS stations within South Korea and the 5 IGS permanent GPS stations around the Korean Peninsula using a global network adjustment. We then calculated the absolute and relative amount of movement of the GPS permanent stations. We also identified the optimum renewal period of the permanent GPS stations considering the accuracy of relative GPS surveying. Finally, we developed a Korean a Korean crustal movement model that can be used to improvement of accuracy.

• Journal of Korean Academy of Nursing Administration
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• v.8 no.3
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• pp.381-392
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• 2002

Purpose : The purpose of this study was to examine the degrees of turnover intention among Korean staff nurses(N=175) and to identify discriminating factors of their turnover intention. Method : The data were driven from a larger study and staff nurses who had worked more than 1 year as nurses were included in the analyses. The original data were collected from May 1999 to March 2000. Descriptive and discriminant analyses were utilized. Results : 87% of the participants reported turnover intention. Nurses were grouped into three group(GP)s depending on the frequencies of turnover intention: Never GP(N=23), Sometimes GP(N=107), Frequent GP(N=43). With three GPs, two functions were produced and only function 1 was significant that significantly discriminated Never and Frequent GPs. Additional discriminant analysis with only Never and Frequent GPs produced function classified 93% of the participants correctly into two GPs. Sub-dimensions of work satisfaction were significant discriminating factors. Nurses who are satisfied with doctor and nurse relationship, pay, and hospital administration tend to report no intention in turnover. Conclusion : Based on the findings of this study, possible managemental intervention for increasing interpersonal skills and assertiveness of nurses, inviting medical residents in ward team meeting, increasing incentives or baseline adjustment of annual income for registered nurses were suggested.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.10a
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• pp.103-107
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• 2003

현재 관측점간의 3차원 상대위치를 구하고 기준점의 측지학적 좌표ㆍ표고를 결정하는 작업을 수행하는 GPS(Global Positioning System) 측량은 신호가 전파인 관계로 대기권의 전파지연 오차를 포함하게 되며, 전리층 지연은 주파수에 반비례하는 특성이 있으므로 지역의 대소에 구분 없이 이주파수 수신기(dual-frequency GPS receiver)를 사용하여 정확하게 지연시간을 측정하고 그로 인한 측위정밀도의 정확성을 확보하고 있다. 본 연구는 비교적 낮은 가격인 일주파 수신기를 사용하여 기선거리별로 삼각점을 선점한 후 동일 시간에 관측을 실시하고 취득한 데이터 값을 추출한 후 기선거리에 따른 허용오차를 분석하고, 그 활용성 및 경제성과 일주파 수신기의 기선에 대한 사용 가능성을 분석하였다. 그 결과, 100km이내의 지역에서는 일주파 수신기 만으로도 충분히 만족스러운 결과를 얻을 수 있었다.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2004.03a
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• pp.535-541
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• 2004

GPS는 직접적인 시통 및 거리에 대해 제한을 받는 일반 재래식 측량으로는 관측하기 힘든 중ㆍ장기선 관측의 경우 기선결정에 대한 정확도와 활용성이 우수하다고 알려져 있다. 그러나 현재 실질적으로 관측하여 취득하고자 하는 위치정보를 얻기 위해 지역의 대소에 관계없이 고가의 이주파 수신 장비를 사용하고 있으며, 최적의 기선해석과 망조정에 의한 성과를 얻기 위한 데이터 처리과정이 엄밀하게 확립되어 있지 않다 이러한 이유들로 인하여 고가의 이주파 수신기가 여러 분야에 적용되고 있으며, 성과물를 산출하고 있는 실정이다. 본 연구에서는 이주파 수신기를 사용하여 전국에 산재하고 있는 국가 기준삼각점을 대상으로 관측을 실시하여, 일주파만을 처리하는 L₁ Only 방식과 이주파를 처리하는 L₁&L₂ 방식과의 비교 분석하여 일주파에 대한 정확도와 적용성 그리고 기선의 거리에 따른 한계성에 대해 검증하고자 한다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.6
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• pp.761-768
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• 2009

GPS data acquired at CORS are widely and rapidly used in many application such as information technology industries. In acquisition of GPS data the establishment of standards of reliability and tolerance error range is necessary. This standards is regarded to contain the requirements of selection of using softwares, precise and broadcast ephemeris, duration of data acquisition, and etc. This study focused to present above standards of tolerance error. In long baseline GPS observation network the RMSE analysed in this study resulted little change when data acquired in 6-hour duration, but the less observation duration resulted less accuracy. Especially in 3-hour observation the accuracy of GPS data decreased rapidly. After analyses of data accuracy in the same observation condition using different computer program between academic and commercial purpose software, the RMSE of academic software resulted less than 1cm compared to 3 to 10cm from commercial software. RMSE analysis between precise ephemeris and broadcast ephemeris resulted similar quantity. Therefore this study regarded to present the reliable establishment of standards of error which can be used in required accuracy in GPS data observation.

• Journal of the Korean earth science society
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• v.34 no.7
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• pp.626-632
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• 2013

In this study the GPS Precipitable Water Vapor (PWV) was derived and evaluated by a radiosode measure during the winter intensive observation in Gangneung site from January 5 till February 29 in 2012. Bernise 5.0 software was used to derive the GPS data. GPS-derived PWV from Zero difference (GANG) and Single difference (GANG and DAEJ) was high variance in time and about 5 times the PWV of radiosonde. GPS post-processing has been performed from two additional IGS site (Xian Dao, Ibaraki-ken) in order to correct the absolute troposphere errors. As a result, the mean bias error (MBE) and root mean square error (RMSE) and correlation compared with radiosonde measure were 0.67 mm, 6.40 mm, and 0.93, respectively. In order to correct the relative troposphere errors from the altitudinal difference between the two GPS receivers, we calculated the GPS-derived PWV by adding the data of GPS that was installed in Gangneung-Wonju University near the Gangwon Regional Meteorological Administration. In the end, the improved result showed that MBE, RMSE and correlation in comparison with radiosonde measures were 0.61 mm, 5.79 mm, and 0.93, respectively.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.185-190
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• 2006

The correct estimation of the ionospheric delays is very important for the precise kinematic positioning especially in case of the long baseline. In case of triple frequency system, the ionospheric delays can be estimated from the measurements, but, in case of dual frequency system, the situation is not so simple. The precision of those supplied by the external information source such as IONEX is not sufficient. The high frequency component is neglected, and the precision of the low frequency component is not sufficient for the long baseline positioning. On the other hand, the high frequency component can be estimated from the phase range measurements. If the low frequency components are estimated by using the external information source or pseudo range measurements, a more reasonable estimation of the ionospheric delays may be possible. It has already been discussed by the author that the estimation of the low frequency components by using the external information source is not sufficient but fairly effective. The estimation using the pseudo range measurements is discussed in the present paper. The accuracy is not sufficient at present because of the errors in the pseudo range measurements. It is clarified that the bias errors in the pseudo range measurements are responsible for the poor accuracy of the ionospheric delays. However, if the accuracy of the pseudo range measurements is improved in future, the method would become very promising.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.10
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• pp.1025-1031
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• 2007

GPS is widely used for positioning applications and attitude of a vehicle can be found also with multiple antennas. However, extremely weak signal level prevents GPS from indoor operation. DR with accelerometers and gyros and landmark based localization method used for indoor applications increase complexity and cost. In this paper, a simple but very efficient ultrasound based attitude determination system which determines both position and attitude in WSN is given. The range between transmitter and receivers are measured using the arrival time difference between ultrasound and RF signal. The 3 dimensional positions can be found using more than 3 range measurements. Furthermore, if more than 2 transmitters are used, the attitude can be determined using the baseline vectors obtained by differencing transmitter and receiver positions. The prototype system is implemented to evaluate the performance of the proposed method. In addition, an error analysis shows the relation between the attitude error and basel me length, quality of measurement and orientation of a vehicle. The static and dynamic experiments performed by micro mobile robot shows accurate position with less than 1.5cm error and attitude with less than 1 degree error can be obtained continuously with 20cm baseline. It is expected that these results can be adapted without modification to indoor applications such as home cleaning robot and autonomous wheelchair maneuvering.

• Journal of Positioning, Navigation, and Timing
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• v.4 no.2
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• pp.79-85
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• 2015

Existing Differential GPS (DGPS) pseudorange correction (PRC) generation techniques based on a virtual reference station cannot effectively assign a weighting factor if the baseline distance between a user and a reference station is not long enough. In this study, a virtual reference station DGPS PRC generation technique was developed based on an enhanced inverse distance weighting method using an exponential function that can maximize a small baseline distance difference due to the dense arrangement of DGPS reference stations in South Korea, and its positioning performance was validated. For the performance verification, the performance of the model developed in this study (EIDW) was compared with those of typical inverse distance weighting (IDW), first- and second-order multiple linear regression analyses (Planar 1 and 2), the model of Abousalem (1996) (Ab_EXP), and the model of Kim (2013) (Kim_EXP). The model developed in the present study had a horizontal accuracy of 53 cm, and the positioning based on the second-order multiple linear regression analysis that showed the highest positioning accuracy among the existing models had a horizontal accuracy of 51 cm, indicating that they have similar levels of performance. Also, when positioning was performed using five reference stations, the horizontal accuracy of the developed model improved by 8 ~ 42% compared to those of the existing models. In particular, the bias was improved by up to 27 cm.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.30 no.1
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• pp.87-96
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• 2012

The U.S. Geological Survey (USGS) announced that an earthquake of 9.0 magnitude had occurred near the east coast of Japan on March 11, 2011, resulting in a displacement of the crust of about 2.4 meters. The Korean peninsula is located on the Eurasian tectonic plate that stretches out to Japan; therefore, there is a high possibility of being affected by an earthquake. The Korean GPS CORS network operated by the National Geographic Information Institute (NGII) was processed for ten days before and after the earthquake. Both static and kinematic baseline processing were tested for the determination of crustal deformation. The static baseline processing was performed in two scenarios: 1) fixing three IGS stations in China, Mongolia and Russia; 2) fixing SUWN, one of the CORS networks in Korea, in order to effectively verify crustal deformation. All data processing was carried out using Bernese V5.0. The test results show that most of the parts of the Korean peninsula have moved to the east, ranging 1.2 to 5.6 cm, compared to the final solution of the day before the earthquake. The stations, such as DOKD and ULLE that are established on the islands closer to the epicenter, have clearly moved the largest amounts. Furthermore, the station CHJU, located on the southwestern part of Korea, presents relatively small changes. The relative positioning between CORS confirms the fact that there were internal distortions of the Korean peninsula to some extent. In addition, the 30-second interval kinematic processing of CORS data gives an indication of earthquake signals with some delays depending on the distance from the epicenter.