• 대한원격탐사학회지
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• 제30권6호
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• pp.755-767
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• 2014

본 연구에서는 LARIAC2 GIS 자료와 전산 유체 역학(CFD) 모델을 이용하여 미국 캘리포니아 주 Los Angeles의 두 지역(Wilshire blvd. & Carondelet and Broadway & $7^{th}$ St.)을 대상으로 수치 실험을 수행하였다. 두 지역의 상세 도시 대기 흐름의 특성을 조사하기 위해 건물 자료 구축 알고리즘을 통해 벡터 형식으로 제공되는 LARIAC2 GIS 자료로부터 건물 도메인 자료를 추출하였다. 추출한 자료를 CFD 모델 입력 자료로 사용하여, 각 지역의 오전과 오후의 주 풍향과 풍속에 대해 수치 실험을 수행하였다. 도시 지역 내에서는 건물에 의해 국소적인 2차 흐름이 발생하면서 유입류와 비교하였을 때, 풍향과 풍속의 차이가 두드러졌다. 유입류와 평행한 방향으로 형성된 도시 협곡에서는 채널링 효과가 나타나면서 풍속이 국지적으로 증가하였고, 수직인 방향으로 형성된 도시 협곡에서는 연직 방향으로 잘 발달한 소용돌이가 형성되었다. 도시 협곡을 이루지 않은 건물의 풍상측에서는 말편자 소용돌이가 지면 근처에서 형성되었고, 풍하측에서는 재순환 영역이 형성되었다. 이와 같은 2차 순환(도시 협곡 소용돌이, 말편자 소용돌이, 재순환 영역)이 형성된 구역에서는 지면 근처의 풍속이 크게 증가하였다. 평균 풍속과 풍향 변화율을 조사한 결과, 대체적으로 풍속 증가율이 높은 곳에서 풍향 변화율이 비교적 낮았고 풍속 감소율이 높은 곳에서는 풍향 변화율이 높게 나타났다.

• 한국항공우주학회지
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• 제35권12호
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• pp.1095-1100
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• 2007

도심지에서는 지형지물 및 건물 등에 의한 영향으로 가시위성 확보가 어려워지게 되며, 이는 사용자 위치결정 및 정확도에 영향을 미친다. 본 논문에서는 3D GIS 수치지도를 이용하여 서울 도심의 특정 지역을 3D 모델로 생성하는 기법에 대해 기술하고, 직선-폴리곤 충돌검사 알고리즘을 적용한 도심지에서의 가시위성 분석 기법 개발 및 필드 실험을 통한 검증을 수행하였다. 도심의 3D 모델을 이용하여 GPS/갈릴레오 단독 수신과 동시 수신의 경우에 대한 가시성을 DOP (Dilution of Precision)관점에서 분석하였다

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.395-400
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• 2006

Among the various error sources in positioning and navigation, the paper focuses on the modeling and prediction of receiver clock bias and then tries to achieve positioning based on simulated and predicted clock bias. With the SA off, it is possible to model receiver clock bias more accurately. We selected several types of GNSS receivers for test using ARMA model. To facilitate prediction with short and limited sample pseudorange observations, AR and ARMA are compared, and the improved AR model is presented to model and predict receiver clock bias based on previous solutions. Our work extends to clock bias prediction and positioning based on predicted clock bias using only 3 satellites that is usually the case under urban canyon situation. In contrast to previous experiences, we find that a receiver clock bias can be well modeled using adopted ARMA model. Test has been done on various types of GNSS receivers to show the validation of developed model. To further develop this work, we compare solution conditions in terms of DOP values when point positioning is conducted using 3 satellites to simulate urban positioning environment. When condition allows, height component is derived from other ways and can be set as known values. Given this condition, location is possible using less than 2 GNSS satellites with fixed height. Solution condition is also discussed for this background using mode of constrained positioning. We finally suggest an effective predictive time span based on our test exploration under varied conditions.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2004년도 춘계학술발표회논문집
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• pp.103-106
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• 2004

Nowadays it is necessary to manage the road system effectively because of the explosive increment of vehicle and goods. To resolve this problems through the fast upgrade of information about position and time of moving vehicle, the combined navigation system using GPS and complementary navigation system, i.e. INS, DR, etc. has been used. Although GPS is popular for the vehicle navigation system, this is not useful for the kinematic positioning of the vehicles in the urban canyon because of its few satellites. Therefore, this study deals with the kinematic positioning of the vehicles with GPS CORS to GPS navigation. For this, first the static single point positioning of GPS and GPS for reference station was performed to evaluate the accuracy of GPS positioning. Next, in the post-processed, the DGPS (Differential GPS) was performed for the kinematic positioning of the vehicles. So, it is expected that GPS CORS can be applicable to the control of traffic flow, the effective management of road system, and the development of ITS and it is regarded that the combined navigation system of vehicles with GPS, INS, and DR, etc. should be studied constantly.

• 한국측량학회지
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• 제19권3호
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• pp.301-308
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• 2001

최근에 GPS가 차량항법시스템으로 큰 역할을 해왔지만, 가로수와 고층빌딩 등이 산재한 도심지에서는 가시위성의 수의 제한으로 연속적으로 정확하게 차량의 동적위치를 결정할 수 없는 실정이다. 이런 GPS의 단점을 보완하기 위해 1996년 완전히 가동된 러시아의 위성항법시스템인 GLONASS를 도입하여 GPS의 보조항법시스템으로 사용하고자 하는 연구가 활발하다. 그래서 본 연구에서는 Real-time code differential positioning 기법으로 차량의 동적위치를 결정하여, Real-time DGG(DGPS/DGLONASS)가 차분측위해의 획득율과 수평위치 정밀도저하율(HDOP ; Horizontal Dilution of Precision)에서 Real-time DGPS보다 훨씬 우수한 값을 얻었으며, 이를 통해 GPS와 GLONASS의 결합이 정확한 차량의 동적위치결정에 기여하고 있음을 알 수 있었다.

• ETRI Journal
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• 제39권2호
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• pp.264-274
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• 2017

Recently, mobile positioning enhancement has attracted much attention in the 3rd generation partnership project long-term evolution system. In particular, for urban canyon environments, the need for three-dimensional (3D) positioning has increased to enable the altitude of users to be measured. For several decades, several time difference of arrival (TDOA-) based 3D positioning methods have been studied; however, they are only available when at least four evolved Node Bs (eNBs) exist nearby or when all eNBs have the same height. Therefore, in this paper, we propose a new 3D positioning method that estimates the 3D coordinates of a user using three types of two-dimensional (2D) TDOAs. However, the give inaccurate results owing to the undefined axis of the 2D coordinate plane. Therefore, we propose a novel derivation of the hyperbola equation, which includes the undefined axis coordinate in the 2D hyperbola equation. Then, we propose an interaction algorithm that mutually supplies the undefined axis coordinate of users among 2D TDOAs. By performing extensive simulations, we verify that the proposed method is the only solution applicable by using three eNBs with different heights.

• 한국측량학회지
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• 제32권6호
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• pp.599-606
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• 2014

Since the accuracy of Global Positioning System (GPS)-based vehicle positioning system is significantly degraded or does not work appropriately in the urban canyon, the integration techniques of GPS with Inertial Navigation System (INS) have intensively been developed to improve the continuity and reliability of positioning. However, its accuracy is degraded as INS errors are not properly corrected due to the GPS signal blockage. Recently, the image-based positioning techniques have been started to apply for the vehicle positioning for the advanced in processing techniques as well as the increased the number of cars installing the camera. In this study, Single Photo Resection (SPR), which calculates the camera exterior orientation parameters using the Ground Control Points (GCPs,) has been integrated with the INS/GPS for continuous and stable positioning. The INS/GPS/SPR integration was implemented in both of a loosely and a tightly coupled modes, based on the Extended Kalman Filter (EKF). In order to analyze the performance of INS/SPR integration during the GPS outage, the simulation tests were conducted with a consideration of factors affecting SPR performance. The results demonstrate that the accuracy of INS/SPR integration is depended on magnitudes of the GCP errors and SPR processing intervals. Additionally, the simulation results suggest some required conditions to achieve accurate and continuous positioning, used the INS/SPR integration.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.3-8
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• 2006

The next decade promises drastic improvements and additions to global navigation satellite systems (GNSS). Plans for GPS modernization include a civilian code measurement on the L2 frequency and a new L5 signal at 1176.45 MHz. Current speculations indicate that a fully operational constellation with these improvements could be available by 2013. Simultaneously, the Galileo Joint Undertaking is in the development and validation stages of introducing a parallel GNSS called Galileo. Galileo will also transmit freely available satellite navigation signals on three frequencies and is scheduled to be fully operational as early as 2008. In other words, a dual system receiver (e.g., GPS+GALILEO) for general users can access six civil frequencies transmitted by at least fifty eights navigation satellites in space. The advent of GALILEO and the modernization of GPS raise a lot of attention to the study of the compatibility and interoperability of the two systems. A number of performance analyses have been conducted in a global scale with respect to availability, reliability, accuracy and integrity in different simulated scenarios (such as open sky and urban canyons) for the two systems individually and when integrated. Therefore, the scope of this article aims at providing the technical benefits analysis for Taiwan specifically in terms of the performance indices mentioned above in a local scale, especially in typical urban canyon scenarios. The conclusions gained by this study will be applied by the Land Survey Bureau of Taiwanese as the guideline for developing future GNSS tracking facilities and dual GNSS processing module for precise surveying applications in static and kinematic modes.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.545-554
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• 2017

Among various applications of the High Altitude Long Endurance (HALE) Unmanned Aerial Vehicle (UAV), this paper has a focus on the Global Positioning System (GPS) utilizing pseudolite and its improved performance, particularly during the multi-purpose missions. In a multi-purpose mission, the HALE UAV follows a specified flight trajectory for both navigation applications and missions. Some of the representative HALE missions are remote exploration, surveillance, reconnaissance, and communication relay. During these operations, the HALE UAV can also be an additional positioning signal source as it broadcast signals using pseudolite. The pseudolite signal can improve the availability, accuracy, and reliability of the GPS particularly in areas with poor signal reception, such as shadowed regions between tall buildings. The improvement in performance of navigation is validated through simulations of multi-purpose missions of the solar-powered HALE UAV in an urban canyon. The simulation includes UAV trajectory generation at stratosphere and uses actual geographical building data. The results indicate that the pseudolite-equipped HALE UAV has the potential to enhance the performance of the satellite navigation system in navigationally degraded regions even during multi-purpose operations.

• 한국항해항만학회지
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• 제26권3호
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• pp.303-310
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• 2002

현재 범세계위치결정체계(GPS)와 추측항법(DR), 기타 장치를 결합한 육상차량항법시스템이 사용되고 있다. 그리고 GPS는 육상항법시스템으로 널리 이용되고 있지만, 도심지 등에서 가시위성의 부족으로 차량의 동적 위치결정에 적절하지 못하다. 따라서 본 연구에서는 GPS의 단점을 보완하기 위해 GPS/GLONASS 결합항법시스템을 이용하여 차량의 동적위치를 결정하였다. 실험결과 도심지에서 많은 장애물과 가시위성에도 불구하고 GLONASS 위성의 부가로 높은 자료획득률을 보여 GPS/GLONASS의 결합항법시스템으로 차량의 동적 위치를 연속적으로 획득할 수 있었다. 그러므로 GPS/GLONASS 결합항법시스템은 도로의 교통흐름의 통제와 효율적 관리에 응용할 수 있을 것으로 사료된다.