• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1098-1104
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• 2011

Data communications networks at sea can be modelled by multi-layered networks with traditional carriers (RF, satellites), and BWA (wireless LAN, WiBro, LTE), which partially makes it possible the high speed communication services (WWW, VoIP) at sea. In this paper, a novel routing scheme (CPR) is proposed which selects an optimal carrier for each hop in routes based on carrier preferences (CP). The carrier preferences are measured proactively depending on the feasibility of transmission characteristics (transmission rate, cost, and latency time) of the carriers for each application. Performance was compared with that of the OMH-MW (Optimal Medium per Hop based on Max-Win) routing scheme.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.61-69
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• 2006

Position determination accuracy is strongly depending on how much precisely and frequently satellite receiver measures transmitted signals from terminals on target animals when Doppler effect is applied for position determination. ARGOS satellite system has shown relatively high position determination accuracy by operating multiple satellites, which enable operator to get more Doppler shift data from terminals. In case of animal tracking mission with single satellite, however, it is difficult for the satellite receiver to receive transmitted signals from terminals frequently during short period that satellite passes over ground terminals. This is one of the main sources to decrease position accuracy on target animals. In this paper, the Doppler rate estimation is implemented to increase the number of Doppler shift data received by single satellite. It is proved that the relatively high position determination accuracy with increased number of estimated data can be obtained. We also suggest that the Doppler rate estimation is applicable for position determination system with single satellite.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.9 no.6
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• pp.1-12
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• 2006

Remote sensing cannot provide a direct measurement of vegetation index (VI) but it can provide a reasonably good estimate of vegetation index, defined as the ratio of satellite bands. The monitoring of vegetation in nearby urban regions is made difficult by the low spatial resolution and temporal resolution image captures. In this study, enhancing spatial resolution method is adapted as to improve a low spatial resolution. Recent studies have successfully estimated normalized difference vegetation index (NDVI) using improved resolution method such as from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard EOS Terra satellite. Image enhancing spatial resolution is an important tool in remote sensing, as many Earth observation satellites provide both high-resolution and low-resolution multi-spectral images. Examples of enhancement of a MODIS multi-spectral image and a MODIS NDVI image of Cheongju using a Landsat TM high-resolution multi-spectral image are presented. The results are compared with that of the IHS technique is presented for enhancing spatial resolution of multi-spectral bands using a higher resolution data set. To provide a continuous monitoring capability for NDVI, in situ measurements of NDVI from paddy field was carried out in 2004 for comparison with remotely sensed MODIS data. We compare and discuss NDVI estimates from MODIS sensors and in-situ spectroradiometer data over Ochang plain region. These results indicate that the MODIS NDVI is underestimated by approximately 50%.

• Journal of Astronomy and Space Sciences
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• v.16 no.1
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• pp.61-68
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• 1999

The radio waves transmitted from GPS satellites is delayed by the troposphere as they propagate to Earth-based GPS receivers. The troposphere delay is usually divided into two parts, the dry delay due to the atmospheric gases and the wet delay due to the water vapor. In this study for the month of May in 1998 the GPS data from two stations(Taejon, Suwon) were used to estimate the total troposphere delay in the zenith direction by the least square method. The dry delay in the zenith direction can be evaluated by using surface pressure values at the station, then the zenith wet delay is obtained by removing the zenith dry delay from the total delay. The zenith wet delay is strongly correlated with the total precipitable water. The quality of the estimate has been assessed by comparison with radiosonde data at Osan. We found the food agreement in precipitable water of the GPS estimates and the radiosonde data. The standard deviation of the difference of the difference between the GPS and radiosonde observations was 3.68mm at Suwon.

• Journal of Astronomy and Space Sciences
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• v.26 no.4
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• pp.529-546
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• 2009

Gauss and Laplace methods for initial orbit determination (IOD) are classical orbit determination tools and have been used very efficiently in optical satellite surveillance system. Several studies related to these two methods have been released until now. In this study, we found that the trends of IOD accuracy for different time interval between three pairs of measurement datas show unexpected results. Therefore, we checked the possible cause of these differences. In order to check various orbit types, we used most of satellite data which is able to obtain. To check the characteristics of methodology-only, we used simulated observation data. And we used real observation data for specific satellites to check the characteristics appeared when we applyed these methods to optical satellite surveillance system. As a result, we found that trends of IOD accuracy for time interval could be different because of satellite position observed.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.6
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• pp.121-130
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• 2009

In this paper, Gaussian probability distribution model based multi-sensor data fusion algorithm is proposed for a vehicular location awareness system. Conventional vehicular location awareness systems are operated by GPS (Global Positioning System). However, the conventional system is not working in the indoor of building or urban area where the receiver is difficult to receive the signal from satellites. A method which is combined GPS and UWB (Ultra Wide-Band) has developed to improve this problem. However, vehicular is difficult to receive seamless location information since the measurement systems by both GPS and UWB convert the vehicle's movement information separately at each sensor. In this paper, normalized probability distribution model based Hybrid UWB/GPS is proposed by utilizing GPS location data and UWB sensor data. Therefore the proposed system provides information with seamless and location flexible properties. The proposed system tested by Ubisense and Asen GPS in the $12m{\times}8m$ outdoor environments. As a result, the proposed system has improved performance for accurateness and connection ability between devices to support various CNS (Car Navigation System).

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.11
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• pp.1126-1132
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• 2009

Bridge structures are designed to support ordinary loadings such as vehicles, wind, temperature and current as well as unexpected loadings like earthquakes and storm. Especially, the displacement of Flexible bridges like an suspension bridge under ordinary loading conditions is necessary to be monitored. In case of long span bridges, there are some difficulties in monitoring the displacement of center of the main span using traditional laser displacement sensors. In this study, the static and dynamic displacement responses due to vehicle loadings were measured by DGPS(differential global positioning system) technique. The displacement response data were compared with data obtained from traditional laser displacement sensors so that the static and dynamic behavior of the bridge under vehicle loadings was examined and the applicability of the displacement response measurement using DGPS technique was verified. The static and dynamic loading test for an self-anchored suspension bridge, So-rok Bridge, was performed using vehicles. The displacement response from DGPS technique and that from laser displacement sensors of the bridge monitoring system were compared. The amplitude of white noise from DGPS based measurement was about 7 mm and that of laser displacement sensor based measurement was about 3 mm. On the other hand, dynamic behavior of the center of main span from DGPS based measurement showed better agreement with influence line of the bridge than that from laser displacement sensors. In addition, there were some irregular and discontinuous variation of data due to the instability of GPS receivers or frequent appearance of GPS satellites. Post-processing via the reference station close to an observation post provided by NGII(National Geographic Information Institute) will be a counter-plan for these defects.

• Aerospace Engineering and Technology
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• v.11 no.1
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• pp.42-48
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• 2012

The telemetry data received from satellite in real-time are used to monitor LEO satellite during the AIT (Assembly, Integration & Test) phase and the mission operation phase after launch. However, it is impossible to check all the incoming telemetry data from satellite in real time in order to detect abnormality of satellite quickly. Especially, the contact time of LEO satellite is limited because of its orbital characteristics. So the anomaly state of the LEO satellite should be detected and resolved during the contact time. Therefore, all incoming spacecraft telemetry data must be selected and manipulated in MIMIC. It is used in order to display summarized information about spacecraft in a visualized way that is quickly and easily understood. That is, it provides essential function to monitor a satellite both in orbit and during testing. In this paper, the design and development of MIMIC currently used in KOMPSAT, a LEO Earth observation satellite is described in detail. In future work, we plan to enhance MIMIC in order to improve user-friendliness and efficiency.

• Atmosphere
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• v.18 no.4
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• pp.267-277
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• 2008

The occurrence and strength of the Asian Dust over the Korea Peninsular have been increased by the expansion of the desert area. For the continuous monitoring of the Asian Dust event, the geostationary satellites provide useful information by detecting the outbreak of the event as well as the long-range transportation of dust. The Infrared Optical Depth Index (IODI) derived from the MTSAT-1R data, indicating a quantitative index of the dust intensity, has been produced in real-time at Korea Meteorological Administration (KMA) since spring of 2007 for the forecast of Asian dust. The data processing algorithm for IODI consists of mainly two steps. The first step is to detect dust area by using brightness temperature difference between two thermal window channels which are influenced with different extinction coefficients by dust. Here we use dynamic threshold values based on the change of surface temperature. In the second step, the IODI is calculated using the ratio between current IR1 brightness temperature and the maximum brightness temperature of the last 10 days which we assume the clear sky. Validation with AOD retrieved from MODIS shows a good agreement over the ocean. Comparison of IODI with the ground based PM10 observation network in Korea shows distinct characteristics depending on the altitude of dust layer estimated from the Lidar data. In the case that the altitude of dust layer is relatively high, the intensity of IODI is larger than that of PM10. On the other hand, when the altitude of dust layer is lower, IODI seems to be relatively small comparing with PM10 measurement.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.16 no.1
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• pp.41-50
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• 1998

The object positional data in the form of digital imagery is processed and stored and is updated easily. The GPS, positioning system using satellites, is acquired its utilities in many parts because it is very easy to get the three dimensional coordinates using GPS around the world. For the effective acquisition of positional data to-ward objects in space, the automation of digital photogrammetry must be done and data acquisition and processing should be performed in real-time. In this study, the program is developed for automatic process of digital photogrammetry and the VAN that has CCD cameras and GPS receivers onboard is built for mobile positioning system. Also, the three dimensional positioning toward 20 objects which are vertical to the ground is done using left and right imagery of CCD cameras and GPS. For a base research in real-time photogrammetry, the three dimensional positioning is performed using continuous imagery and GPS and the three dimensional positioning accuracy is analyzed.