• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.6
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• pp.628-636
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• 2014

This paper describes the design and analysis of five-element planar array antenna of an anti-jamming satellite navigation system. We propose a design of multi-layer patch antenna for Global Positioning System(GPS) $L_1/L_2$ dual bands. The proposed antenna has two ports feeding network with a hybrid chip coupler for a broad bandwidth with Right-Handed Circular Polarization(RHCP). The measurement results show the bore-sight gains of 1.10 dBic($L_1$) and 0.37 dBic($L_2$) for the center element. The bore-sight gains of an edge element are 0.99 dBic($L_1$) and -0.57 dBic($L_2$). At a fixed elevation angle of $30^{\circ}$, antennas show average gains of -2.08 dBic ($L_1$) and -5.33 dBic($L_2$) for the center element, and average gains of -0.40 dBic($L_1$) and -2.09 dBic($L_2$) for the edge elements. The results demonstrate that the proposed array antenna is suitable for anti-jamming applications.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.80-80
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• 2016

GPS로 대표되는 위성항법시스템(GNSS : Global Navigation Satellite System)은 지구 주위를 돌면서 연속적으로 항법신호를 보내고 있다. 그 중 지구표면으로부터 반사되는 항법신호를 수신하고 해석함으로써 지구표면에 관한 정보를 취득할 수가 있다. GPS로 대표되는 항법신호는 L밴드를 사용하기 때문에 토양수분의 변화 등에 대한 반사강도의 감도가 비교적 높다고 알려져 있으며, 토양수분 측정 등에 사용할 수 있다. 뿐만 아니라 경량화, 소형화하기 쉬운 점, 능동적 마이크로웨이브 리모트센싱시스템(Active Microwave Remote Sensing System)과 달리 스스로 신호를 발사하지 않기 때문에 관측의 스텔스성(Stealth)dl 뛰어난 점 등의 장점을 가지고 있다. 또한 향후 10년 이내에 준천정위성(QZSS), Galileo, COMPAS, IRNSS 등 많은 위성항법시스템이 본격 운용되어 GPS와 함께 120기 정도의 항법위성이 항법신호를 송신할 예정이므로 이용 가능성은 크게 늘어날 것으로 기대된다.한편, 항법위성을 이용한 바이스테이틱 리모트센싱은 반사파의 강도가 상당히 미약하기 때문에 정량적 계측모델의 구축은 미미한 상태이다. 즉, 지상 타워에서의 관측, 항공기에서의 관측, 소형 위성에서의 관측 등이 수행되고 있으나, 타워관측과 같이 지상의 거의 동일한 장소를 계속적으로 관측하는 경우를 제외한 기존의 연구에서는 토지의 피복상황이나 토양수분 등의 상관관계를 제시하는 수준으로써 정량적인 계측방법은 아직 확립되어 있지 않다. 이러한 관점에서 본 연구에서는 GPS위성으로부터의 항법신호를 이용하여 지구표면에 관한 정보를 얻는 바이스테이틱 리모트센싱(Bi-static Remote Sensing) 기술을 바탕으로 육지면과 해면의 판별에 신호특성이 어떻게 유효한가를 실험적으로 밝혔다. 이러한 기술은 토양수분 측정 등 수자 원인자를 추출하는데 유용할 뿐만 아니라 수면의 고도 측정, 해상풍 산출 등에도 응용 가능하다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2011.06a
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• pp.27-28
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• 2011

A 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 satellite's life span about 5 to 10 years which can be resulted in economic loss considering the amount of multi-billion won. This paper analyzed the recent solar storm of X-class occurred on 15th of February about 10:45 this year that was reached Korea (Bohyun observatory) on 18th of February about 10:30 (local time), and compared with the data of before and after a week. The proton data of 18th of February considered that the solar strom reached on earth showed a fluctuation compared to the data of before and after a week. The positioning results at Daejeon also showed higher positioning error compared to the data of before and after a week results.

• Korean Journal of Remote Sensing
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• v.37 no.5_1
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• pp.1135-1147
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• 2021

In order to geometrically correct high-resolution satellite imagery, the sensor modeling process that restores the geometric relationship between the satellite sensor and the ground surface at the image acquisition time is required. In general, high-resolution satellites provide RPC (Rational Polynomial Coefficient) information, but the vendor-provided RPC includes geometric distortion caused by the position and orientation of the satellite sensor. GCP (Ground Control Point) is generally used to correct the RPC errors. The representative method of acquiring GCP is field survey to obtain accurate ground coordinates. However, it is difficult to find the GCP in the satellite image due to the quality of the image, land cover change, relief displacement, etc. By using image maps acquired from various sensors as reference data, it is possible to automate the collection of GCP through the image matching algorithm. In this study, the RPC of KOMPSAT-3A satellite image was corrected through the extracted matching point using the UAV (Unmanned Aerial Vehichle) imagery. We propose a pre-porocessing method for the extraction of matching points between the UAV imagery and KOMPSAT-3A satellite image. To this end, the characteristics of matching points extracted by independently applying the SURF (Speeded-Up Robust Features) and the phase correlation, which are representative feature-based matching method and area-based matching method, respectively, were compared. The RPC adjustment parameters were calculated using the matching points extracted through each algorithm. In order to verify the performance and usability of the proposed method, it was compared with the GCP-based RPC correction result. The GCP-based method showed an improvement of correction accuracy by 2.14 pixels for the sample and 5.43 pixelsfor the line compared to the vendor-provided RPC. In the proposed method using SURF and phase correlation methods, the accuracy of sample was improved by 0.83 pixels and 1.49 pixels, and that of line wasimproved by 4.81 pixels and 5.19 pixels, respectively, compared to the vendor-provided RPC. Through the experimental results, the proposed method using the UAV imagery presented the possibility as an alternative to the GCP-based method for the RPC correction.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.5
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• pp.403-412
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• 2018

Recently, GNSS (Global Navigation Satellite System)-derived orthometric height determination has been studied to improve the time and cost-effectiveness of traditional leveling surveying. However, the accuracy of this new survey method was evaluated when unknown points are located lower than control points. In this study, the accuracy of GNSS-derived orthometric height was examined using TPs (Triangulation Points) to verify the stability of surveying in mountainous areas. The GNSS survey data were obtained from Mungyeong, Unbong/Hadong, Uljin, and Jangseong. Three unknown points were surrounded by more than three UCPs (Unified Control Points) or BMs (Benchmarks) following the guideline for applying GNSS-derived orthometric height determination. A newly developed national geoid model, KNGeoid17 (Korean National Geoid 2017), has been applied for determining the orthometric height. In comparison with the official orthometric heights of the TPs, the heights of the unknown points in Mungyeong and Unbong/Hadong differ by more than 20 cm. On the other hand, TPs in Uljin and Jangseong show 15-16 cm of local bias with respect to the official products. Since the precision of official orthometric heights of TPs is known to be about 10 cm, these errors exceed the limit of the precision. Therefore, the official products should be checked to offer more reliable results to surveyors. As an alternative method of verifying accuracy, three different GNSS post-processing software were applied, and the results from each software were compared. The results showed that the differences in the whole test areas did not exceed 5 cm. Therefore, it was concluded that the precision of the GNSS-derived orthometric height was less than 5 cm, even though the unknown points were higher than the control points.

• Journal of Korean Society for Geospatial Information Science
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• v.25 no.2
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• pp.57-65
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• 2017

The purpose of this study is to analyze the feasibility of using Global Navigation Satellite System(GNSS)/Geoid technology in determining orthometric height in mountain. For the study, a test bed was set up in and around Mount Jiri and GNSS surveying were conducted. The orthometric height of 39 benchmarks was determined by applying the EGM2008, KNGeoid13, and KNGeoid14 geoid models and the accuracy was estimated by comparing with the offical Benchmarks orthometric height value issued by National Geographic Information Institute(NGII) and finally, the results were analyzed with the Aerial Photogrammetry Work Regulations. As a result of the study, it was found that the accuracy of the orthometric height determination by GNSS/Geoid technology was ${\pm}7.1cm$ when the KNGeoid14 geoid model was applied. And also, it can be confirmed that it is usable for the less than 1/1000 plotting scales as a vertical reference point for the aerial triangulation in Aerial Photogrammetry.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1433-1440
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• 2015

In this paper, we propose an unambiguous correlation function to improve tracking performance for binary offset carrier (BOC) signals. Specifically, we divide a BOC sub-carrier into multiple rectangular pulses, and analyze that the BOC autocorrelation function is made up of the sum of several partial correlation functions. Then, we obtain two sub-correlation functions by combining two partial correlation functions and propose a novel unambiguous correlation function with no side-peak which can be regulated its width based on the combination of the sub-correlation functions and partial correlation functions. From numerical results, it is confirmed that the proposed correlation function provides a tracking performance improvement over the conventional correlation functions in terms of the tracking error standard deviation.

• Journal of the Korea Society of Computer and Information
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• v.20 no.2
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• pp.79-88
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• 2015

This paper introduces surveillance equipment "ADS-B", the core subject of traffic control system and study of ADS-B 1090ES ground receiver. The standard is set not only for functional but also its reliability by analyzing international standard documents and existing products. The Bias circuit is designed for less power consumption, low noise and high gain for RF module. The signal processing is capable of overcoming its bad conditions. MCU part is configured with the latest CPU for high speed communication with external parts and SNMP is selected for remote control communication. The performance of developed receiver satisfies national and international standards and its functions are more advanced compared to foreign receivers.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.11
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• pp.2745-2752
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• 2014

In recent years, Transport Demand Management has been conducted for the efficient management of transport. In ITS applications in particular, the prerequisite is accurate and reliable positioning. However, the major problems are satellite signal outage, and multipath. This paper proposes that outage and multipath measurement can be detected and estimated using elevation angle and signal to noise ratio data association relation in stand-alone GPS. In order to verify the performance of the proposed method, it is then evaluated by the car test. the evaluation test environment has low accuracy and unreliable positioning because of signal outage or multipath such as steep hill and high buildings. In the evaluation test result, 918times abnormal signal occurred and it was confirmed that the proposed method showed more improved 9.48m(RMS) horizontal positioning error than without proposed method.

• Journal of Astronomy and Space Sciences
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• v.30 no.4
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• pp.315-320
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• 2013

Space geodetic techniques can be used to obtain precise shape and rotation information of the Earth. To achieve this, the representative combination solution of each space geodetic technique has to be produced, and then those solutions need to be combined. In this study, the representative combination solution of very long baseline interferometry (VLBI), which is one of the space geodetic techniques, was produced, and the variations in the position coordinate of each station during 7 years were analyzed. Products from five analysis centers of the International VLBI Service for Geodesy and Astrometry (IVS) were used as the input data, and Bernese 5.0, which is the global navigation satellite system (GNSS) data processing software, was used. The analysis of the coordinate time series for the 43 VLBI stations indicated that the latitude component error was about 15.6 mm, the longitude component error was about 37.7 mm, and the height component error was about 30.9 mm, with respect to the reference frame, International Terrestrial Reference Frame 2008 (ITRF2008). The velocity vector of the 42 stations excluding the YEBES station showed a magnitude difference of 7.3 mm/yr (30.2%) and a direction difference of $13.8^{\circ}$ (3.8%), with respect to ITRF2008. Among these, the 10 stations in Europe showed a magnitude difference of 7.8 mm/yr (30.3%) and a direction difference of $3.7^{\circ}$ (1.0%), while the 14 stations in North America showed a magnitude difference of 2.7 mm/yr (15.8%) and a direction difference of $10.3^{\circ}$ (2.9%).