• Korean Journal of Remote Sensing
• /
• v.37 no.6_1
• /
• pp.1657-1667
• /
• 2021

Anthropogenic activities and natural processes have been causes of land subsidence which is sudden sinking or gradual settlement of the earth's solid surface. Mexico City, the capital of Mexico, is one of the most severe land subsidence areas which are resulted from excessive groundwater extraction. Because groundwater is the primary water resource occupies almost 70% of total water usage in the city. Traditional terrestrial observations like the Global Navigation Satellite System (GNSS) or leveling survey have been preferred to measure land subsidence accurately. Although the GNSS observations have highly accurate information of the surfaces' displacement with a very high temporal resolution, it has often been limited due to its sparse spatial resolution and highly time-consuming and high cost. However, space-based synthetic aperture radar (SAR) interferometry has been widely used as a powerful tool to monitor surfaces' displacement with high spatial resolution and high accuracy from mm to cm-scale, regardless of day-or-night and weather conditions. In this paper, advanced interferometric approaches have been applied to get a time-series of land subsidence of Mexico City using four-year-long twenty ALOS PALSAR L-band observations acquired from Feb-11, 2007 to Feb-22, 2011. We utilized persistent scatterer interferometry (PSI) and small baseline subset (SBAS) techniques to suppress atmospheric artifacts and topography errors. The results show that the maximum subsidence rates of the PSI and SBAS method were -29.5 cm/year and -27.0 cm/year, respectively. In addition, we discuss the different subsidence rates where the study area is discriminated into three districts according to distinctive geotechnical characteristics. The significant subsidence rate occurred in the lacustrine sediments with higher compressibility than harder bedrock.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
• /
• 2007.04a
• /
• pp.77-80
• /
• 2007

In this paper GPS data for the period from January 2002 to June 2004 (910 days) were analyzed to quantitatively investigate the plate deformation patterns and distributions in the Korean peninsula. The GPS network is composed of 45 permanent GPS stations. The daily data were analyzed using the GAMIT/GLOBK software and the precise orbits generated by the International GNSS Service (IGS). The research result make it possible to understand the tendency of crustal movement in and around the Korean peninsula, which have an effect on the occurrence of earthquake.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.4
• /
• pp.372-382
• /
• 2009

A GNSS software for processing the SBAS correction data is developed, and Japan MSAS correction data is analyzed. MSAS orbit correction data is analyzed and compared with WAAS data. MSAS ionosphere correction data is analyzed and the effect of the equatorial anomaly on the correction accuracy is discussed. Degradation due to receive delay of correction information and effect of the degradation on protection level analyzed using partial remove of MSAS correction information. Integrity and availability for precision approch using the MSAS system analyzed.

• Journal of Institute of Control, Robotics and Systems
• /
• v.19 no.2
• /
• pp.102-106
• /
• 2013

A cooperative navigation method for cooperative flight of UAVs is proposed. The commonly used navigation method for UAVs is based on GNSS measurements. However, when it is not available by jamming or other causes, an alternative method is needed. In this paper, it is shown that UAVs equipped with inertial sensors, passive sensor and wireless communication link can perform accurate navigation through sharing information with each other. Firstly, the appropriate roles for sensors and wireless communication link are assigned. Secondly, a filter to perform navigation cooperative is constructed. Finally, the boundedness of estimation error of the filter under small initial estimation error is analyzed. The simulation results show that the proposed method can reduce navigation errors effectively.

• Journal of Positioning, Navigation, and Timing
• /
• v.2 no.1
• /
• pp.49-57
• /
• 2013

When pseudolite navigation system is applied to wide area, the tropospheric delay is the main error factor. In this study, we experimentally compared and analyzed the performance of the conventional pseudolite tropospheric delay models. The integration method using radiosonde meteorological data was suggested to derive the reference value for the comparison and analysis. Flight tests were carried out to analyze the performance of the tropospheric delay models according to the elevation angle and distance conditions between the user receiver and the pseudolite. As the results of this study, we provided the basis for the choice of tropospheric delay model appropriate to the relative location characteristics of the pseudolite and the user.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2010.10a
• /
• pp.25-27
• /
• 2010

국제해사기구(IMO) 제52차 NAV 회의에서 처음 소개된 e-Navigation은 그동안 국제항로표지협회(IALA), 국제수로기구(IHO), 국제통신연맹(ITU) 및 국제전기표준위원회(IEC)에서 많은 정책과 기술사항이 검토되어 왔다. 본 논문에서는 IALA e-NAV 제8차 기술위원회('10.9.20-24)에 참석하여 관련 국제기구에서 진행중인 e-Navigation 추진현황과 동향을 파악하여 앞으로 우리나라의 대응방향을 논하고자 한다.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
• /
• 2010.09a
• /
• pp.152-155
• /
• 2010

본 연구에서는 서울특별시 네트워크 RTK 시스템의 활용 및 Virtual RINEX 실용성 검토를 위해 수행하였다. 네트워크 RTK 시스템의 활용 다양화를 위해서는 NTRIP을 통하여 타기관의 사용자 시스템으로 실시간 전송, 시설물의 변위에 대한 GNSS로 모니터링 방법, GNSS Internet Radio Client와 Radio Modem을 이용한 RTK측위를 소개하고, Virtual RINEX 실용성 검토는 VRS RTK 측위 결과와 이동국 측위 지점에 대한 Virtual RINEX 데이터의 후처리 성과를 비교하였다. 그 결과, Virtual RINEX와 GPS 관측 성과는 거의 동일하여 향후 Virtual RINEX도 후처리 데이터로 사용할 수 있는 가능성을 확인하였고, VRS RTK 측위 성과는 Virtual RINEX 후처리 성과와 수 mm 이내 차이를 보여 산출된 성과가 거의 같음을 확인할 수 있었다.

• Journal of Positioning, Navigation, and Timing
• /
• v.5 no.4
• /
• pp.165-172
• /
• 2016

A Global Navigation Satellite System (GNSS), which is typically exemplified by the Global Positioning System (GPS), employs a open signal structure so it is vulnerable to spoofing electronic attack using a similar malicious signal with that used in the GPS. It is necessary to require a spoofing test evaluation environment to check the risk of spoofing attack and evaluate the performance of a newly developed anti-spoofing technique against spoofing attacks. The present paper proposed a simulation method of spoofing environment based on simulator that can be implementable in a test room and analyzed the spoofing simulation performance using commercial GPS receivers. The implemented spoofing simulation system ran synchronized two GPS simulator modules in a single scenario to generate both of spoofing and GPS signals simultaneously. Because the signals are generated in radio frequency, a commercial GPS receiver can be tested using this system. Experimental test shows the availability of this system, and anti-spoofing performance of a commercial GPS receiver has been analyzed.

• Journal of Positioning, Navigation, and Timing
• /
• v.5 no.4
• /
• pp.173-180
• /
• 2016

This paper presents a method to suppress multipath induced by pulses using supervised learning. In modern electronics, pulses have been used for various purposes such as communication or distance measurements. Like other signals, pulses also suffer from multipath. When a pulse and a multipath are overlapped, the original pulse shape is distorted. The distorted pulse could result in communication failures or distance measurement errors. However, a large number of samples available from a pulse can be used to effectively reject multipath by using a supervised learning method. This paper introduces how a supervised learning method can be applied to Distance Measuring Equipment. Simulation results show that multipath induced distance measuring error can be suppressed by 10 ~ 45 percent depending on the allowed pulse shape variation allowed in a standard.

• Electronics and Telecommunications Trends
• /
• v.31 no.3
• /
• pp.20-31
• /
• 2016

위성항법 보강시스템은 항법위성인 GPS 제공 항법신호를 수신 처리하여 각종 오차 성분을 제거시킴으로써 산출된 위치정확도, 시스템 가용도 및 제공신호에 대한 무결성 등이 향상됨에 따라 항공분야, 해양분야 및 차량내비 등 육상분야에서 요구하는 위치정확도뿐만 아니라 보강 및 무결정정보 등을 특정 성능 요구를 만족시킬 수 있도록 제공하는 시스템이다. GPS 신호에 대한 오차를 보강한 메시지를 활용하는 매체를 무엇을 활용하는지에 따라 구분할 수 있는데 위성을 이용하면 위성기반 보강시스템(Satellite Based Augmentation System: SBAS), 지상망을 이용하면 지상기반 보강시스템(Ground Based Augmentation System: GBAS), 비행기를 이용하면 항공기반보강시스템(Aircraft-Based Augmentation System: ABAS)으로 일컫는다. 본고에서는 위성항법 보강시스템의 현황과 그 관련 기술에 대하여 기술하고 한다.