• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2022년도 학술발표회
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• pp.153-153
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• 2022

Large-scale and accurate observations at fine spatial resolution through a means of remote sensing offer an effective tool for capturing rainfall variability over the traditional rain gauges and weather radars. Although satellite rainfall products (SRPs) derived using two major estimation approaches were evaluated worldwide, their practical applications suffered from limitations. In particular, the traditional top-down SRPs (e.g., IMERG), which are based on direct estimation of rain rate from microwave satellite observations, are mainly restricted with their coarse spatial resolution, while applications of the bottom-up approach, which allows backward estimation of rainfall from soil moisture signals, to novel high spatial resolution soil moisture satellite sensors over South Korea are not introduced. Thus, this study aims to evaluate the performances of a state-of-the-art bottom-up SRP (the self-calibrated SM2RAIN model) applied to the C-band SAR Sentinel-1, a statistically downscaled version of the conventional top-down IMERG SRP, and their integration for a targeted high spatial resolution of 0.01° (~ 1-km) over central South Korea, where the differences in climate zones (coastal region vs. mainland region) and vegetation covers (croplands vs. mixed forests) are highlighted. The results indicated that each single SRP can provide plus points in distinct climatic and vegetated conditions, while their drawbacks have existed. Superior performance was obtained by merging these individual SRPs, providing preliminary results on a complementary high spatial resolution SRP over central South Korea. This study results shed light on the further development of integration framework and a complementary high spatial resolution rainfall product from multi-satellite sensors as well as multi-observing systems (integrated gauge-radar-satellite) extending for entire South Korea, toward the demands for urban hydrology and microscale agriculture.

• 한국전자통신학회논문지
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• 제13권4호
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• pp.713-720
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• 2018

신호의 도래각(: Angle-of-Arrival, AOA) 추정기법, 간섭제거 기술, 및 송신 빔형성 기법 등을 기반으로 하는 신호정보 수집(: Signal Intelligence, SIGINT) 시스템은 다양한 신호정보를 효율적으로 수집하기 위해 요구되는 핵심 기술이다. 본 논문에서는 도래각 추정기, 적응 빔형성기, 신호처리 및 D/B 유닛, 송신 빔형성기로 구성된 신호정보 수집을 위한 위성 시스템의 효율적인 구조를 소개한다. 제시된 구조는 다양한 신호의 정확한 도래각 추정을 위해 MUSIC(: Multiple Signal Classification) 알고리즘을 사용하고, 불필요한 간섭 또는 재밍 신호를 제거하기 위해 MVDR(: Minimum Variance Distortionless Response) 기법을 사용하며, 수집된 정보 및 데이터의 효과적인 송신을 위해 MMSE(: Minimum Mean Square Error) 기반의 송신 빔형성 기법을 적용한다. 또한, 컴퓨터 시뮬레이션을 통해 소개된 위성 시스템의 성능을 평가하고 분석한다.

• Journal of Positioning, Navigation, and Timing
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• 제4권2호
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• pp.43-55
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• 2015

In the case of satellite navigation positioning, the shielding of satellite signals is determined by the environment of the region at which a user is located, and the navigation performance is determined accordingly. The accuracy of user position determination varies depending on the dilution of precision (DOP) which is a measuring index for the geometric characteristics of visible satellites; and if the minimum visible satellites are not secured, position determination is impossible. Currently, the GLObal NAvigation Satellite system (GLONASS) of Russia is used to supplement the navigation performance of the Global Positioning System (GPS) in regions where GPS cannot be used. In addition, the European Satellite Navigation System (Galileo) of the European Union, the Chinese Satellite Navigation System (BeiDou) of China, the Quasi-Zenith Satellite System (QZSS) of Japan, and the Indian Regional Navigation Satellite System (IRNSS) of India are aimed to achieve the full operational capability (FOC) operation of the navigation system. Thus, the number of satellites available for navigation would rapidly increase, particularly in the Asian region; and when integrated navigation is performed, the improvement of navigation performance is expected to be much larger than that in other regions. To secure a stable and prompt position solution, GPS-GLONASS integrated navigation is generally performed at present. However, as available satellite navigation systems have been diversified, finding the minimum satellite constellation combination to obtain the best navigation performance has recently become an issue. For this purpose, it is necessary to examine and predict the navigation performance that could be obtained by the addition of the third satellite navigation system in addition to GPS-GLONASS. In this study, the current status of the integrated navigation performance for various satellite constellation combinations was analyzed based on 2014, and the navigation performance in 2020 was predicted based on the FOC plan of the satellite navigation system for each country. For this prediction, the orbital elements and nominal almanac data of satellite navigation systems that can be observed in the Korean Peninsula were organized, and the minimum elevation angle expecting signal shielding was established based on Matlab and the performance was predicted in terms of DOP. In the case of integrated navigation, a time offset determination algorithm needs to be considered in order to estimate the clock error between navigation systems, and it was analyzed using two kinds of methods: a satellite navigation message based estimation method and a receiver based method where a user directly performs estimation. This simulation is expected to be used as an index for the establishment of the minimum satellite constellation for obtaining the best navigation performance.

• 한국위성정보통신학회논문지
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• 제10권4호
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• pp.58-63
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• 2015

GPS(Global Positioning System는 지구상에서 약 2km 떨어진 위성으로부터 송신한 신호를 수신하므로 그 수신감도가 매우 낮아 재밍과 간섭에 매우 취약하다. 따라서 GPS 수신단에서 항재밍 능력에 대한 필요성은 점점 증가하고 있다. 이러한 GPS의 취약성을 이용하여 전시 상황에서 적군은 재밍 기법을 이용하여 수신단에서 아군의 GPS 신호를 이용한 정확한 측위를 방해한다. 따라서 전시상황에 대비하여 재밍 환경에 대응하고, 측위 정보를 획득할 수 있는 방법이 필요하다. 본 연구에서는 재밍 환경에서의 측위 정확도를 향상시키기 위해 BSS(Blind Source Separation) 기법을 사용하여 GPS 신호와 재밍 신호를 분리하는 방법을 제안한다. 또 재밍신호와 분리된 GPS 신호에는 여전히 잡음(noise)이 존재해 정확한 측위 정보를 획득하기 어렵다. 따라서 잡음을 효과적으로 제거하기 위해 웨이블릿 임계화 기법을 사용한다. 실험 결과는 본 연구실에서 수행한 GPS/QZSS/Wi-Fi 밀결합 측위기법의 테스트 결과를 이용하여 재밍 환경에서의 BSS 와 웨이블릿 임계화 기법을 통한 정확도 향상을 보이며 제안한 시스템 모델의 우수성을 입증한다.

• 한국위성정보통신학회논문지
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• 제12권1호
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• pp.64-71
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• 2017

본 논문은 저 비용, 저 소비전력으로 실내외에서 수십 cm급의 정밀한 위치인식이 가능한 IR-UWB(Impulse-Radio Ultra Wideband) Radar 시스템에서 정확한 목표물을 추정하고자 Kalman 필터 및 RRWA 알고리즘을 사용하였다. 목표물에 의해 반사된 신호에는 목표물 신호이외에 불필요한 신호들이 존재한다. 불필요한 신호들을 제거하고 정확한 목표물 신호를 도출 및 성능 향상을 위해 노력하였다. 하나의 송신 안테나와 수신안테나로 목표물들의 위치를 실시간으로 추정한다. Kalman 필터를 사용하여 배경잡음을 제거하였고 RRWA 알고리즘을 사용하여 반사파 신호를 제거하여 기존의 목표물 신호를 추정했을 때보다 더 좋은 성능을 보였다. 본 논문에서는 향후 진행 되어질 목표물 추정에 있어 정확한 거리 추정 및 추적을 하는 연구에 도움이 될 것이라 생각한다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
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• pp.892-895
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• 2006

The atmospheric effects on the retrieval of sea ice concentration from passive microwave sensors are examined using simulated data typical for the Arctic summer. The simulation includes atmospheric contributions of cloud liquid water and water vapor and surface wind on surface emissivity on the microwave signatures. A plane parallel radiative transfer model is used to compute brightness temperatures at SSM/I frequencies over surfaces that contain open water, first-year (FY) ice and multi-year (MY) ice and their combinations. Synthetic retrievals in this study use the NASA Team (NT) algorithm for the estimation of sea ice concentrations. This study shows that if the satellite sensor’s field of view is filled with only FY ice the retrieval is not much affected by the atmospheric conditions due to the high contrast between emission signals from FY ice surface and the signals from the atmosphere. Pure MY ice concentration is generally underestimated due to the low MY ice surface emissivity that results in the enhancement of emission signals from the atmospheric parameters. Simulation results in marginal ice areas also show that the atmospheric and surface effects tend to degrade the accuracy at low sea ice concentration. FY ice concentration is overestimated and MY ice concentration is underestimated in the presence of atmospheric water and surface wind at low ice concentration. In particular, our results suggest that strong surface wind is more important than atmospheric water in contributing to the retrieval errors of total ice concentrations over marginal ice zones.

• 한국항행학회논문지
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• 제18권4호
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• pp.312-318
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• 2014

본 연구의 대상인 정지궤도위성은 GPS위성 궤도보다 높은 고도에 위치하기 때문에 지상 사용자에 비하여 GPS 신호의 가시성과 신호 세기 면에서 큰 차이가 있다. 본 연구에서는 이러한 정지궤도위성환경에 탑재되는 GPS 수신기에서의 GPS 위성 신호 가시성을 분석하고, 미약신호 획득 및 추적 알고리즘인 CCMDB 알고리즘을 적용하여 정지궤도위성 탑재 GPS 수신기에서 활용 가능한 소프트웨어 GPS 수신기를 개발하였다. 개발된 소프트웨어 GPS 수신기의 검증을 위하여 상용 하드웨어 시뮬레이터로 정지궤도위성 탑재 GPS 수신기에서 수신되는 GPS 신호를 생성하였고 이를 처리하여 성능을 분석하였다. 항법해 계산 결과 평균 3축 위치 및 속도 오차는 각각 165.636 m와 0.5081 m/s로 계산되었다.

• 한국위성정보통신학회논문지
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• 제7권1호
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• pp.128-133
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• 2012

본 논문에서는 기만신호의 영향을 분석하기 위하여 기만신호의 코드지연에 따른 코드 및 반송파 추적에 대한 결과를 분석하였다. 기만신호의 특성 및 방어 방법에 대한 조사를 통하여 현재 GPS 신호와 동기를 유지할 수 있는 중급기만을 고려하여 기만신호생성기를 이용하여 시뮬레이션을 수행하였다. 기만신호생성기에서 생성한 정상신호 및 기만신호가 합성된 신호를 소프트웨어 수신기를 통하여 신호처리를 수행하였다. 본 논문에서는 코드추적루프(DLL) 및 위상추적루프(PLL)의 출력값을 비교분석하여 기만신호의 영향을 파악하였으며 또한 기만신호 인가 시 잘못된 의사거리에 따른 항법해의 영향을 분석하였다. 결과적으로 기만신호의 영향은 신호추적 단계에서는 1칩 이내의 코드지연을 갖는 기만신호의 영향을 받으며 신호획득에서는 코드 지연에 상관없이 영향을 받는 것을 확인하였다.

• 대한원격탐사학회지
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• 제26권3호
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• pp.297-304
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• 2010

Since the change in Doppler centroid according to moving targets brings alteration to the phase in azimuth differential signals of synthetic aperture radar (SAR) data, one can measure the velocity of the moving targets using this effect. In this study, we will investigate theoretically measuring the velocity of an object from azimuth differential signals by using range compressed data which is the interim outcome of treatment from the simulated SAR raw data of moving targets on the background of sea clutter. Also, it will provide evaluation for the elements that affect the estimation error of velocity from a single SAR sensor. By making RADARSAT-1 simulated image as a specific case, the research includes comparisons for the means of velocity measurement classified by the directions of movement in the four following cases. 1. A case of a single target without currents, 2. A case of a single target with tidal currents of 0.5 m/s, 1 m/s, and 3 m/s, 3. A case of two targets on a same azimuth line moving in a same direction and velocity, 4. A case of a single target contiguous to land where radar backscatter is strong. As a result, when two moving targets exist in SAR image outside the range of approximately 256 pixels, the velocity of the object can be measured with high accuracy. However, when other moving targets exist in the range of approximately 128 pixels or when the target was contiguous to the land of strong backscatter coefficient (NRCS: normalized radar cross section), the estimated velocity was in error by 10% at the maximum. This is because in the process of assuming the target's location, an error occurs due to the differential signals affected by other scatterers.

• 대한원격탐사학회지
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• 제35권1호
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• pp.39-55
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• 2019

In this study, we have proposed an improved method to detect forest fires by correcting the reflected signals of day images using the middle-wavelength infrared (MWIR) channel. The proposed method is allowed to remove the reflected signals only using the image itself without an existing data source such as a land-cover map or atmospheric data. It includes the processing steps for calculating a solar-reflected signal such as 1) a simple correction model of the atmospheric transmittance for the MWIR channel and 2) calculating the image-based reflectance. We tested the performance of the method using the MODIS product. When compared to the conventional MODIS fire detection algorithm (MOD14 collection 6), the total number of detected fires was improved by approximately 17%. Most of all, the detection of fires improved by approximately 30% in the high reflection areas of the images. Moreover, the false alarm caused by artificial objects was clearly reduced and a confidence level analysis of the undetected fires showed that the proposed method had much better performance. The proposed method would be applicable to most satellite sensors with MWIR and thermal infrared channels. Especially for geostationary satellites such as GOES-R, HIMAWARI-8/9 and GeoKompsat-2A, the short acquisition time would greatly improve the performance of the proposed fire detection algorithm because reflected signals in the geostationary satellite images frequently vary according to solar zenith angle.