• Journal of Advanced Navigation Technology
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• v.22 no.4
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• pp.271-278
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• 2018

For ionospheric correction of low earth orbiter (LEO) satellites using single frequency global navigation satellite system (GNSS) receiver, ionospheric scale factor should be applied to the ground-based ionosphere model. The ionospheric scale factor can be calculated by using a NeQuick model, which provides a three-dimensional ionospheric distribution. In this study, the ionospheric scale factor is calculated by using NeQuick G model during 2015, and it is compared with the scale factor computed from the combination of LEO satellite measurements and international GNSS service (IGS) global ionosphere map (GIM). The accuracy of the ionospheric delay calculated by the NeQuick G model and IGS GIM with NeQuick G scale factor is analyzed. In addition, ionospheric delay errors calculated by the NeQuick G model and IGS GIM with the NeQuick G scale factor are compared. The ionospheric delay error variations along to latitude and solar activity are also analyzed. The mean ionospheric scale factor from the NeQuick G model is 0.269 in 2015. The ionospheric delay error of IGS GIM with NeQuick G scale factor is 23.7% less than that of NeQuick G model.

• Proceedings of the KSRS Conference
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• v.2
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• pp.684-687
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• 2006

Airborne imagery must be precisely orthorectified to be used as geographical information data. GPS/INS (Global Positioning System/Inertial Navigation System) and LIDAR (LIght Detection And Ranging) data were employed to automatically orthorectify airborne images. In this study, 154 frame airborne images and LIDAR vector data were acquired. LIDAR vector data were converted to raster image for employing as reference data. To derive images with constant brightness, flat field correction was applied to the whole images. The airborne images were geometrically corrected by calculating internal orientation and external orientation using GPS/INS data and then orthorectified using LIDAR digital elevation model image. The precision of orthorectified images was validated using 50 ground control points collected in arbitrary selected five images and LIDAR intensity image. In validation results, RMSE (Root Mean Square Error) was 0.365 smaller then two times of pixel spatial resolution at the surface. It is possible that the derived mosaicked airborne image by this automatic orthorectification method is employed as geographical information data.

• Journal of Satellite, Information and Communications
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• v.8 no.1
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• pp.40-44
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• 2013

In this paper, we describe on the position error of GBAS. In reality, there are many sources which make errors into the calculation of receiver position. It is well known that the DOP of GBAS is an important position error source and is dependent on the numbers and positions of the transmitters. Here, we develop an algorism to calculate the DOP of the GNSS with 2-line transmitters into Korean area. The result is useful to predict the DOP of the positions where transmitters and receivers are located.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.15 no.2
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• pp.18-24
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• 2007

The high ionospheric spatial gradient during ionospheric storm is the most concern when applying GNSS(Global Navigation Satellite System) augmentation systems for aircraft precision approach. Since the ionospheric gradient level depends on geographical location as well as the storm, understanding the ionospheric gradient statistics over a specific regional area is necessary for operating the augmentation systems. This paper compares three ionosphere gradient computation methods, direct differentiation between two receivers' ionospheric delay signal for a common satellite, derivation from a grid ionosphere map, and derivation from a plate ionosphere map. The plate map method provides a good indication on the gradient variation behavior over a regional area with limited number of GNSS receivers. The residual analysis for the ionosphere storm detection is discussed as well.

• Journal of the Korean Institute of Navigation
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• v.17 no.2
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• pp.75-106
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• 1993

GMDSS(Global Maritime Distress and Safety system) is a new communication system for the distress and safety at sea which is utilizing the recent advancements in satellite communication and positioning system, digital communication system, computer and microelectronic technology, etc., and will completely substitute the current communication system by 1999. Although the improvements of education for producing qualified Radio Operators as well as the establi-shments of policy for accepting the system are required, the educational institutions and relating administ-rations have not yet prepared the rational and concrete schemes on the educational methods and accepting procedures for the system. In this study, as the result of analyzing the GMDSS, courses of training and relating data, the authors suggested principles for improving the course and contents of education and rational schemes for balan-cing the demand and supply of Radio Operators. The authors expect not only the consequences of this study can be utilized as reference materials for the instruction to ratio communication in the organs of education but also that the following effects can be obtained by the study. 1. Security of distress and safety communication system at sea by the establishment of relating regula-tions. 2. Rationalization of the management of radio communication at sea and improvement of the communi-cation system on the vessel. 3. Upgrading the quality of Radio Operators and presenting schemes for current qualified persons. 4. Activation of industry producing radio instruments. 5. Balance of the demand and supply of Radio Operators and development of shipping industry.

• Journal of Positioning, Navigation, and Timing
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• v.5 no.2
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• pp.67-74
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• 2016

In this paper, time comparison is performed with standardization institution in Japan using a Two-Way Satellite Time and Frequency Transfer (TWSTFT) technique as one of the methods for high precision time comparison. To analyze the performance of time comparison in the TWSTFT method, time comparison results via the Global Positioning System (GPS) code and carrier wave are analyzed. Through the time comparison performance, frequency stability is analyzed using modified Allan deviation and by this result, characteristics of time comparison of the TWSTFT that is utilized in international time comparison are presented.

• Journal of the Korean earth science society
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• v.42 no.4
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• pp.445-458
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• 2021

Gravity Recovery and Climate Experiment (GRACE) gravimeter satellites observed the Earth gravity field with unprecedented accuracy since 2002. After the termination of GRACE mission, GRACE Follow-on (GFO) satellites successively observe global gravity field, but there is missing period between GRACE and GFO about one year. Many previous studies estimated terrestrial water storage (TWS) changes using hydrological models, vertical displacements from global navigation satellite system observations, altimetry, and satellite laser ranging for a continuity of GRACE and GFO data. Recently, in order to predict TWS changes, various machine learning methods are developed such as artificial neural network and multi-linear regression. Previous studies used hydrological and climate data simultaneously as input data of the learning process. Further, they excluded linear trends in input data and GRACE/GFO data because the trend components obtained from GRACE/GFO data were assumed to be the same for other periods. However, hydrological models include high uncertainties, and observational period of GRACE/GFO is not long enough to estimate reliable TWS trends. In this study, we used convolutional neural networks (CNN) method incorporating only climate data set (temperature, evaporation, and precipitation) to predict TWS variations in the missing period of GRACE/GFO. We also make CNN model learn the linear trend of GRACE/GFO data. In most river basins considered in this study, our CNN model successfully predicts seasonal and long-term variations of TWS change.

• Journal of the Korean Association of Geographic Information Studies
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• v.14 no.1
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• pp.118-129
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• 2011

This Study has developed the information system of the rivers based on 3D image GIS by converging the latest information technology of GIS(Geographic Information System), RS(Remote Sensing), GNSS(Global Navigation Satellite System), aerial laser survey(LiDAR) with real time network technology in order to understand the current situation of all the four major rivers and support the administrative management system. The said information system acquires the high resolution aerial photographs of 25cm, aerial laser survey and water depth surveying data to express precise space information on the whole Youngsan River which is the leading project site out of the four river sites. Monitoring the site is made available on the transporting means such as a helicopter, boat or a bus in connection with locational coordinate tracking skill for the moving objects in real time using GNSS. It makes monitoring all the information on the four river job sites available at a glance, which can obtain the reliability of the people to such vast areas along with enhancing the recognition of the people by publicity of four Rivers Revitalizing Project and reports thereof.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.2
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• pp.327-334
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• 2020

In this paper, an automatic cruise system of unmanned boat was developed for surveying water depth in reservoir using accurate location information. Using global satellite navigation system(GNSS) data in real time, this unmanned system, combined with an echo sounder, can simultaneously collect location information and depth information on the reservoir. This automatic navigation system allows the automatic route generation program to automatically generate a cruise route according to the input conditions for grid sizes of 5m, 10m and 20m, and automatically controls the cruise route with high positional accuracy. The developed system was tested to verify the applicability of the selected Yonggok(Geoncheon) reservoir as a test reservoir located in Suncheon, Jeollanam-do.

• Journal of Advanced Navigation Technology
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• v.12 no.6
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• pp.539-547
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• 2008

In this paper, preliminary results for design of prototype ADS-ADS-B/TIS-B Validation Testbed (AVT) are described. Automatic Dependent Surveillance (ADS-B) is a novel surveillance concept using the Global Navigation Satellite System (GNSS) and a digital datalink. Air traffic information from ADS-B non-equipped aircraft is not acquired since ADS-B is a dependent surveillance. Traffic Information Service-Broadcast (TIS-B) provides surveillance data from Secondary surveillance Radar (SSR) for ADS-B non-equipped aircraft. AVT is based on ADS-B and TIS-B as an integrated platform for air traffic surveillance system for CNS/ATM.