• Journal of Positioning, Navigation, and Timing
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• 제11권4호
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• pp.251-261
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• 2022

The Centimeter Level Augmentation Service (CLAS) is the Precise Point Positioning (PPP) - Real Time Kinematic (RTK) correction service utilizing the Quasi-Zenith Satellite System (QZSS) L6 (1278.65 MHz) signal to broadcast the Global Navigation Satellite System (GNSS) error corrections. Compact State-Space Representation (CSSR) corrections for mitigating GNSS measurement error sources such as satellite orbit, clock, code and phase biases, tropospheric error, ionospheric error are estimated from the ground segment of QZSS CLAS using the code and carrier-phase measurements collected in the Japan's GNSS Earth Observation Network (GEONET). Since the CLAS service begun on November 1, 2018, users with dedicated receivers can perform cm-level precise positioning using CSSR corrections. In this paper, CLAS-based VRS-RTK performance evaluation was performed using Global Positioning System (GPS) observables collected from the refence station, TSK2, located in Japan. As a result of performing GPS-only RTK positioning using the open-source software CLASLIB and RTKLIB, it took about 15 minutes to resolve the carrier-phase ambiguities, and the RTK fix rate was only about 41%. Also, the Root Mean Squares (RMS) values of position errors (fixed only) are about 4cm horizontally and 7 cm vertically.

• Journal of Positioning, Navigation, and Timing
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• 제10권2호
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• pp.103-111
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• 2021

A series of experiments have been carried out by using National Geographic Information Institute(NGII)'s Continuously Operating Reference Station (CORS) data with various strategies to analyze the impact of multi-GNSS measurements on baseline processing. The results of baseline processing were compared in terms of ambiguity fixing rate, precision, and hypothesis tests were conducted to confirm the statistical difference. The combination of multi-GNSS measurements has helped to improve ambiguity fixing rate, especially under harsh positioning environments. Combination of GPS, Galileo, BeiDou could get better precision than that of GPS, GLONASS, Galileo, and adding QZSS made the baseline solution's vertical component more precisely. The hypothesis tests have statistically confirmed that the inclusion of the multi-GNSS in the baseline processing enables not only to reduce field observation time length but also to enhance the solution's precision. However, it is of interest to notice that results of the baseline solution are dependent upon the software used. Hence, comprehensive studies should be performed shortly to derive the best practice to select the appropriate software.

• 한국항해학회지
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• 제17권3호
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• pp.49-55
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• 1993

This study describes the accuracies of position fixes observed by the DGPS systems for the purpose of obtaining the utility basic data in the fishery and oceanography observation field. The circling sail experiments around a reterence point using the DGPS were made in water level point of National Fisheries University of Pusan and on the sea in Yongho day located on the southeast of that university. The main results are as follows ; 1) The number of the usable satellites in position fixing were all eighteen, SV 2, 3, 11-21, 23-26 and SV 28 etc. Each satellites could be observed for average seven hours a day, and position fixing was found to be always possible except about thirty minutes a day. 2) In the standard fixed position, the radius of 95% probability circle and the shifted distance between the position fixes by the DGPS and true position were respectively 5.7m, 0.9m. In the above case those of ordinary GPS was respectively 48.8, 54.2m. Therefore, the accuracy of the position fixes by DGPS was shown much higher the ordinary GPS. 3) At land, the shifted distance between the center of traces in the circling sail experiment of 15m ra-dius by DGPS and the reference position amounted to 5.5m and observed radius of circling traces was 17.5m. other than 15m. At sea, that distance the center of traces in circling experiment of 20m radius by the DGPS and the reference position amounted to 3.6m and observed radius of circling traces was 19.7m, other than 20m. Therefore, the utility of the circling experiment to obtain the accurate position fixes by the DGPS was found to be very high.

• 한국지리정보학회지
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• 제13권1호
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• pp.28-34
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• 2010

소나무재선충병 피해의 공간적 분포 특성은 고사목 단목 중심의 점상 발생을 보이기 때문에 신속한 피해지 파악과 정확한 확산예측에 어려움이 있다. 따라서 피해발생 조기예찰 및 분석, 감시 감독이 매우 중요하다. 그러나 기존의 예찰방법인 도로나 민가 주변 중심의 지상 육안예찰은 누락된 지역이 많고 고산지역, 급경사, 절벽등의 위험지역 예찰이 불가능하기 때문에 본 연구에서는 이러한 단점들을 보완하기 위하여 체계적이고 과학적인 GIS, GPS와 헬기를 이용한 항공정밀예찰 기법을 개발하였으며, 2005년 전국 32개 시 군(약 $28,810km^2$) 피해지역의 349지점 972본의 고사목 위치좌표를 취득하여 소나무재선충병 방제에 활용하였다. 따라서 항공정밀예찰기법 개발은 소나무재선충병 발생 우려지역에 대한 고사목 색출 및 고사원인 규명, 매개충 산란처 제거 등의 효과를 얻을 수 있을 것이다.

• 한국습지학회지
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• 제15권4호
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• pp.567-572
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• 2013

포유동물은 생태계에 중요한 역할을 담당하고 있으며 환경의 변화를 파악하기 위해서는 장기적인 연구가 필수이다. 고라니는 한국 고유종으로 풍부한 개체수가 존재하지만 고라니의 서식지의 생태적 특징과 행동권에 대한 자료가 부족하다 따라서 본 연구는 우리나라 고유종인 고라니의 행동연구를 위해 GPS 장치를 부착하였다. 연구 결과 주간활동이 야간보다 서식반경이 큰 것으로 나타났으며, 봄철이 겨울철 및 다른 계절보다 월등하게 큰 것으로 나타났다, 고라니의 대부분 토지이용은 산림 및 습지와 농경지인 것으로 나타났다. 본 연구는 고라니의 서식지 행동을 측정함으로써 행동생태학에 대한 중요성을 알 수 있었다. 또한 환경변화에 따른 포유류의 행동반경의 변화를 연구하기 위해서 후속적인 연구가 필요할 것이다.

• Asian Pacific Journal of Cancer Prevention
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• 제17권9호
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• pp.4313-4318
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• 2016

Background: This study documented the performance of providers of visual inspection with acetic acid (VIA) at primary health centers, assessing their compliance with the VIA skills checklist and determinants of non-compliance, and exploring their perceptions of VIA training sessions. Materials and Methods: A cross-sectional study was conducted among VIA providers in the $Mekn\grave{e}s$-Tafilalet region of Morocco. Structured observation of their performance was conducted through supervisory visits and multiple focus group discussions (FGDs). Results: Performance of all the recommended steps for effective communication was observed in a low proportion of procedures (36.4%). Midwives/nurses had higher compliance than general practitioners (GPs) (p<0.001). All recommended steps for VIA examination were performed for a high proportion of procedures (82.5%). Compliance was higher among midwives/nurses than among GPs (p<0.001) and among providers in rural areas than those in urban areas (p<0.001). For pre-VIA counselling, all recommended steps were performed for only 36.8% of procedures. For post-VIA counseling, all recommended steps were performed in a high proportion (85.5% for VIA-negative and 85.1% for VIA-positive women). Midwives/nurses had higher compliance than GPs when advising VIA-positive women (p=0.009). All infection prevention practices were followed for only 14.2% of procedures, and compliance was higher among providers in rural areas than those in urban areas (p<0.001). Most FGD participants were satisfied with the content of VIA training sessions. However, they suggested periodic refresher training and supportive supervision. Conclusions: Quality assurance of a cervical cancer screening program is a key element to ensure that the providers perform VIA correctly and confidently.

• 한국소음진동공학회논문집
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• 제19권11호
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• pp.1126-1132
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• 2009

Bridge structures are designed to support ordinary loadings such as vehicles, wind, temperature and current as well as unexpected loadings like earthquakes and storm. Especially, the displacement of Flexible bridges like an suspension bridge under ordinary loading conditions is necessary to be monitored. In case of long span bridges, there are some difficulties in monitoring the displacement of center of the main span using traditional laser displacement sensors. In this study, the static and dynamic displacement responses due to vehicle loadings were measured by DGPS(differential global positioning system) technique. The displacement response data were compared with data obtained from traditional laser displacement sensors so that the static and dynamic behavior of the bridge under vehicle loadings was examined and the applicability of the displacement response measurement using DGPS technique was verified. The static and dynamic loading test for an self-anchored suspension bridge, So-rok Bridge, was performed using vehicles. The displacement response from DGPS technique and that from laser displacement sensors of the bridge monitoring system were compared. The amplitude of white noise from DGPS based measurement was about 7 mm and that of laser displacement sensor based measurement was about 3 mm. On the other hand, dynamic behavior of the center of main span from DGPS based measurement showed better agreement with influence line of the bridge than that from laser displacement sensors. In addition, there were some irregular and discontinuous variation of data due to the instability of GPS receivers or frequent appearance of GPS satellites. Post-processing via the reference station close to an observation post provided by NGII(National Geographic Information Institute) will be a counter-plan for these defects.

• 한국측량학회지
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• 제21권2호
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• pp.137-145
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• 2003

Echo Sounder와 GPS의 조합에 의한 3차원 지형측량은 최근 해양 및 하천에서의 구조물 설치, 준설 및 매립, 해저 및 하상 지형변화 관측 등 그 활용도가 매우 높아지고 있다. 이 경우 수심측량의 오차는 GPS와 Echo Sounder의 조합에 의해 발생되는 형태와 Echo Sounder자체에서 발생되는 형태로 나눌 수 있다. 본 연구에서는 Echo Sounder자체에서 발생하는 경우에 있어 특히 음파의 반사면인 해저, 하상의 지질 상태에 따른 오차를 분석하고 해결방안을 제시하고자 한다. 이를 위해 실제 하구하상에서 채취한 시료를 이용한 수조 실험을 수행하여 평균입도-Echo Sounder 잔차와의 관계를 파악 오차보정식을 제시하고, 제시된 오차보정식의 신뢰도를 높이기 위해 검증시험을 수행하였다. 그 결과 하구하상 지형측량시 측량대상지의 지질 상태를 사전 조사, 사전 측량하면 Echo Sounder의해 발생된 오차의 크기를 추정, 보정할 수 있는 오차 보정식을 제시하였다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.535-540
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• 2006

The relationship between the observable noise model and the satellite elevation angle can be modeled quite well by an exponential function.[Jin, 1996] Noise size and dependence on the elevation angle are, however, different for each observation and receiver type. Therefore, the coefficient determination of this model is an issue, and various methods including PR-CP, single difference, and time difference have been suggested. The limitations of them are difficulty to model the carrier phase noise and to eliminate bias. To overcome these disadvantages for using Jin's model, we suggest zero baseline double difference (DD) and noise sorting algorithm. Data DD technique in zero baseline is useful to eliminate all the troublesome GPS biases, and the remaining error is the sum of GPS measurement noises from two satellites. These DD residuals for hours should be sorted by the combination of satellite elevation angles, and then variance value of the residual for each combination can be estimated. Using these values, we construct an over-determined linear equation whose solution is a set of noise variance for each satellite elevation angle. With 24hr Trimble 4000ssi data, we easily worked out the coefficients of the noise model not only for pseudorange but also for carrier phase. We estimated the standard deviation of the measurement DD using our model, and plotted 1 and 3 sigma lines for every epoch to verify the representation of the residual error. 63.3% of pseudorange residual and 65.9% of phase error did not exceed the 1 sigma lines. Additionally, 99.2% and 99.5% of them lied within 3sigma line. These figures prove that the Gaussian property of measurement noise, and that the suggested model by our algorithm corresponds to the observable noise information.

• Journal of Astronomy and Space Sciences
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• 제33권4호
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• pp.287-293
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• 2016

The equatorial region of the Earth's ionosphere exhibits large temporal variations in electron density that have significant implications on satellite signal transmissions. In this paper, the first observation results of the variations in the trough of the equatorial ionospheric anomaly at the permanent Global Navigation Satellite System (GNSS) site in Chuuk (Geographic: $7.5^{\circ}N$, $151.9^{\circ}E$; Geomagnetic: $0.4^{\circ}N$) are presented. It was found that the daytime Global Positioning System (GPS) total electron content (TEC) values vary according to the 27 day period of solar rotation, and that these trends show sharp contrast with those of summer. The amplitudes of the semi-annual anomaly were 12.4 TECU (33 %) on $19^{th}$ of March and 8.8 TECU (23 %) on $25^{th}$ of October respectively, with a yearly averaged value of 38.0 TECU. The equinoctial asymmetry at the March equinox was higher than that at the October equinox rather than the November equinox. Daily mean TEC values were higher in December than in June, which could be interpreted as annual or winter anomalies. The nighttime GPS TEC enhancements during 20:00-24:00 LT also exhibited the semi-annual variation. The pre-midnight TEC enhancement could be explained with the slow loss process of electron density that is largely produced during the daytime of equinox. However, the significant peaks around 22:00-23:00 LT at the spring equinox require other mechanisms other than the slow loss process of the electron density.