Deuk-Jae Cho

How sun spot activity affects on positioning accuracy?: Case study of solar storm

태양 흑점수의 증감주기 (약 11년)에 따른 태양폭발 (태양에서의 플레어 현상)은 태양 코로나 물질을 대방출하는 태양폭풍을 야기한다. 미국해양대기청 (NOAA: National Oceanic and Atmospheric Administration)은 태양 흑점활동이 2013년과 2014년 사이에 극대화 될 것이라고 예상했다. 강력한 태양폭풍의 영향이 지구에 미쳤을 경우 인공위성을 이용한 전 세계 측위시스템의 교란, 각종 통신수단 및 TV, 라디오 방송 등이 영향을 받을 것으로 예상된다. 실제로 1989년 태양폭풍은 캐나다에서 정전사태를 일으켜 9시간동안 약 600만 명이 정전으로 인한 피해를 입은 사례가 있다. 이와 같은 초강력 태양폭풍은 인공위성의 수명을 약 5~10년 정도 단축시키며 이로 인한 경제적 손실 및 파급효과를 고려하면 액수는 수십조 원에 달할 것으로 예상된다. 최근 2011년 2월 15일 10시 45분경 (01:30 - UTC)에 발생했던 X급 태양폭발에 의해 발생한 태양폭풍의 영향이 2011년 2월 18일 오전 10시 30분경 우리나라 (보현산 관측소)에서 관측되었다. 본 논문에서는 현재 흑점수가 증가하고 있는 시점에서 2월 18일의 태양폭발 일주일 전후 지자기 데이터를 비교하고, 또한 대전과 서울지역에서 관측한 RINEX 데이터를 이용하여 측위결과를 비교 분석하였다. 태양폭풍이 지구에 도달한 2011년 2월 18일의 지자기 관측값은 일주일 전후 데이터와 비교하여 양자(Proton) 자력계 관측결과가 요동하였고, 대전과 서울지역에서의 측위결과도 태양폭풍 일주일 전후와 비교하여 2월 18일에 가장 큰 측위오차를 보였다. 【Solar flares have the 11-year cycle and release a large energy which may produce coronal mass ejections (CME). The NOAA (National Oceanic and Atmospheric Administration) predicted that the sun spot activity will be maximized in 2013-2014. A strong solar flare can cause the disturbance of global positioning system including various communication of TV, radio broadcasting. The actual solar storm in 1989 caused power outages in Canada during 9 hours and about 600 million people had experienced a blackout. Such a solar storm can shorten the GPS satellites life span about 5 to 10 years which can resulted in economic loss considering the amount of multi-billion won. This paper analyzed the influence of recent X-class solar storm occurred on 15th of February about 10:45 this year that was reached Korea (Bohyun observatory) on 18th of February about 10:30 (01:30 - UTC), and compared with the data before and after a week. The proton data of 18th of February considered that the solar storm reached on earth showed a fluctuation compared to the data before and after a week. The positioning results at Daejeon and Seoul of Korea also showed higher positioning error compared to the data before and after a week results.】

Detection algorithm of ionospheric delay anomaly based on multi-reference stations for ionospheric scintillation

Radio waves including GPS signals, various TV communications, and radio broadcasting can be disturbed by a strong solar storm, which may occur due to solar flares and produce an ionospheric delay anomaly in the ionosphere according to the change of total electron content. Electron density irregularities can cause deep signal fading, frequently known as ionospheric scintillation, which can result in the positioning error using GPS signal. This paper proposes a detection algorithm for the ionosphere delay anomaly during a solar storm by using multi-reference stations. Different TEC grid which has irregular electron density was applied above one reference station. Then the ionospheric delay in zenith direction applied different TEC will show comparatively large ionospheric zenith delay due to the electron irregularity. The ionospheric slant delay applied an elevation angle at reference station was analyzed to detect the ionospheric delay anomaly that can result in positioning error. A simulation test was implemented and a proposed detection algorithm using data logged by four reference stations was applied to detect the ionospheric delay anomaly compared to a criterion.

A Study on Integrity Monitoring Improvement of the DGPS Reference Station

The importance of the GPS is becoming larger and larger since it is one of the Global Navigation Satellite Systems and is regarded as a national infrastructure in the field positioning and timing Nowadays many researches avoiding and/or minimizing economic loss caused by unexpected fault of the GPS are being carried out because GPS fault can give a large impact on social security system as well as economic system NDGPS network which has been authorized by the Ministry of Marine and Fisheries provides services for marine users and evolved into a national infrastructure for GNSS users. Many researchers and engineers are doing research work in order to apply the NDGPS network to other fields. From this trend, it can be expected that the integrity and related functions for the NDGPS users will become more important than before. This paper analyzes integrity informations about the real GNSS fault and proposes method on integrity monitoring improvement of the DGPS reference station.

A Comparative Analysis of Performance of Ambiguity Validation Methods

반송파를 이용한 정밀 측위의 성능은 미지정수 결정에 큰 영향을 받는다. 미지정수가 정확하게 결정되면 수 mm에서 수 cm 정도의 정밀한 위치해를 얻을 수 있지만 미지정수가 잘못 결정되면 위치해의 정밀도와 정확도를 보장할 수 없다. 미지 정수 결정은 Integer Rounding(IR), Integer Bootstrapping (IB), Integer Least Squares(ILS) 등의 기법을 기반으로 발전 되어 왔다(Blewitt, 1989; Dong and Bock, 1989; Teunissen, 1993). 이 중에서 ILS를 기반으로 하는 기법이 이론과 실험의 모든 측면에서 다른 기법들보다 좋은 성능을 보이기 때문에 많은 연구에서 언급되고 있다. 특히, Teunissen(1995)은 ILS 를 수행하기 전에 비상관화 과정을 이용하여 미지정수 결정 성공률 및 효율성을 비약적으로 발전시켰다. ILS를 기반으로 하는 미지정수 결정은 다음과 같은 단계로 이루어진다. 첫 번 째는 미지정수가 정수라는 제약조건을 실수영역으로 완화하 여 실수 미지정수(floating ambiguity)와 실수 미지정수의 공 분산행렬을 추정한다. 두 번째는 앞서 추정한 실수 미지정수 와 실수 미지정수의 공분산행렬로 표현되는 비용함수를 최소 화시키는 정수 미지정수(integer ambiguity) 후보를 정수영역 에서 검색한다. 세 번째는 정수 미지정수 후보에 대한 검정을 통해 최종적으로 미지정수를 결정한다. IR, IB를 기반으로 하 는 방법들은 하나의 정수 미지정수 후보를 계산한다. 이에 반 해 ILS는 검색을 통해 여러 개의 정수 미지정수 후보를 찾으 므로, 후보 간의 검정을 통해 신뢰성이 가장 높게 평가된 하나 의 후보를 최종적인 미지정수로 결정하거나 모든 후보가 신뢰 성이 같게 평가되는 경우에는 미지정수를 결정하지 못하는 상 황으로 판단한다. 후보에 대한 검정이 견고하지 못하면 잘못 미지정수 후보 타당성 검정 기법간의 비교 분석

Design of Monitoring System for Network RTK

Network RTK is a precise positioning technique using carrier phase correction data from reference stations within the network, and is constantly being researched for improved performance. However, the study for the system accuracy has been performed but system integrity research has not been done as much as system accuracy, because network RTK has been mainly used on surveying for static or kinematic positioning. In this paper, adequate monitoring system for network RTK is designed as basis research for integrity monitoring on network RTK. To this, fault tree on network RTK is analyzed, and a countermeasure is prepared to detect and identify the each fault items. Based these algorithms, monitoring system to use on central processing facility is designed for network RTK service.

Design of Transportation Safety system with GPS Precise Point Positioning

*,†Marine Safety Research Division, Maritime and Ocean Engineering Research Institute, KIOST, Daejeon, Korea요 약 :해양 사고는 대부분 지형지물, 혼잡한 해상교통 및 기상악화 등에 의한 충돌 사고이다. 따라서 안전한 통항을 위해서는 정확한 정보를 토대로 사전에 통항안전을 판단하여야 하지만, 정보가 부족하거나 부정확하다면 통항안전 판단이 어렵게 된다. 따라서 다양하고 정확한 환경 정보를 토대로 사전에 통항안전을 정확하게 제공할 수 있는 시스템이 필요하다. 본 논문에서는 선박의 통항안전을 예측하는 시스템을 구성하였다. 제안한 시스템은 항로 내 지형지물 정보에 대한 데이터베이스를 포함하며, 정확한 위치 정보를 토대로 현재 선박의 위치와 각 요소 사이의 수평 또는 수직 간격을 계산한다. 본 논문에서는 정확한 선박의 3차원 위치를 구하기 위하여, PPP 기반의 GPS 항법 알고리즘을 적용하였다. 또한, 기상악화로 인하여 시계가 불안정하더라도 항해가 가능하도록 데이터베이스 기반의 3차원 모니터링 기능을 추가하였다. 아울러 실제로 경인아라뱃길과 선박의 정보를 이용하여 시스템을 구성하고, 기능 및 성능을 평가하였다.핵심용어 : 해양 사고, 선박통항안전시스템, GPS, PPP, 경인아라뱃길Abstract : Most of the maritime accidents are the crash that occurred by complex coastal terrain, increased maritime traffic and frequent weather changes. Therefore, transportation safety is exactly determined using accurate environmental informations, but if informations are inaccurate or insufficient, accident risk can be increased. Therefore, ship need the system that can accurately generate transportation safety information. This paper proposes the transportation safety system and performance evaluation in the real environment. The proposed system includes database of environment informations and navigation algorithm using PPP method to estimate the accurate ship position. Therefore, this system can accurately calculate distance or freeboard between ship with other factors. Futhermore, when weather is deteriorated, crew can sail with database based 3-D monitoring module in the transportation safety system . To verify the function and performance, data of Kyungin ARA waterway and ferry is used to evaluation.Key words :Maritime Accident, Transportation Safety System, GPS, PPP, Kyungin ARA Waterway†교신저자 : 연회원, sephil@kiost.ac 042)866-3695* 연회원, djcho@kiost.ac 042)866-3683* 연회원, parksg@kiost.ac 042)866-3685* 연회원, hush@kiost.ac 042)866-3661* 종신회원, spark@kiost.ac 042)866-3681* 종신회원, shsuh@kiost.ac 042)866-3000

Software designs for enhanced maritime service options

Herein, we focus on the design of software RSIM for enhanced maritime DGNSS operation and its service. First, it describes the architecture of RS and 1M systems, and analyzes the performance requirements of the RTCM SC-104 document. In order to achieve this study, we proposed the design of the software for the DGNSS RSIM architecture, operational module for the control and monitoring of GNSS receivers, module for generating the differential corrections and converting to RTCM format, and it then broadcasts the differential corrections to user receivers using the MSK modulator. For the performance requirements of the proposed software RSIM, the pseudorange (PR) measurement, the pseudorange corrections (PRCs) and position accuracy are presented in the Interests of performance analysis of the software RSIM. We then analyze the functionality of maritime DGNSS integrity monitoring and the key components for generations of 1M information. In addition, we present the performance analysis results of the proposed software DGNSS RSIM. Finally, our conclusions are presented.

GPS Anomaly Analysis and Pseudorange Accuracy Improvement by Anomalous Satellite Elimination

GPS anomaly has increased according to the degradation of satellite performance, and many GPS users could be exposed to any kinds of error-included signals without any previous notice when unscheduled error occurred. RSIM (Reference Station Integrity Monitors) is a typical monitoring method to broadcast PRC (Pseudo Range Correction) for users. However, there were some cases that the receiver detected the anomalous satellites signal even though it was unhealthy set, consequently it occurred a large range error. Then it is important to monitor the integrity of GPS signal and it is needed to devise the correction method of pseudorange by eliminating error-occurred PRN for notification to GPS users when it is monitored that the anomaly occurred. This paper proposes the basic concept of how to correct the pseudorange. The paper also shows the analysis results of PRN10 GPS anomaly occurred on day 39 in 2007 with corrected results by eliminating anomaly satellite (PRN10). The proposed correction method shows decreased pseudorange error range compared to the case when the anomaly satellite were used.

A Study on Design of Reference Stations and Integrity Monitors for Maritime DGPS Recapitalization

Hardware dedicated off-the-shelf maritime differential GPS RSIM lacks the open architecture to meet all the minimum maritime user requirements and to include future GNSS improvements after recapitalization. This paper carries out a study to replace existing hardware dedicated differential GPS RSIM with software differential GPS RSIM in order to make up the weak point of hardware dedicated off-the-shelf maritime differential GPS RSIM. In this paper, the architecture of software RSIM is proposed for maritime DGPS recapitalization. And the feasibility analysis of the proposed software differential GPS RSIM is performed as the first phase to realize the proposed architecture. For the feasibility analysis, the prototype RF module and DSP module are implemented with properties as wide RF bandwidth, high sampling frequency, and high speed transmission interface. This paper shows that the proposed architecture has the possibility of real time operation of software RSIM functionality onto the PC-based platform through the analysis of computation time. Finally, this paper verifies that the L1/L2 dual frequency software differential RSIM designed according to the proposed method satisfies the performance specifications set out in RTCM paper 221-2006-SC104-STD.

A Study of GPS Precise Ephemeris Interpolation for Maritime Precise Positioning Applications

Currently many vessels determine an overhead obstruction by a rule of thumb based on their draft for maritime navigation. Therefore they doesn`t have a good overhead obstruction clearance because vertical position of vessels varies on time by tidal. As a result, it is occurred maritime accidents that the mainmast of vessels is bumped against overhead facilities. And disaster by global warming and rising sea levels have increased casualties. So we feel keenly the necessity of warning system for not an earthquake but disaster wave such a tsunami. This paper analyzes a precise GPS ephemeris for maritime precise positioning to solve these problems. The precise GPS ephemeris provided by International GNSS service gives a difficulty to real-time application because of its sample interval. This paper proposes an effective interpolation method for real-time application, and it analyzes an accuracy of precise GPS ephemeris through an interpolation method.