• 대한원격탐사학회지
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• 제33권1호
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• pp.1-13
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• 2017

This study investigates the geometric and spatial image quality analysis of KOMPSAT-3A stereo pair. KOMPSAT-3A is, the latest satellite of KOMPSAT family, a Korean earth observation satellite operating in optical bands. A KOMPSAT-3A stereo pair was taken on 23 November, 2015 with 0.55 m ground sampling distance over Terrassa area of Spain. The convergence angle of KOMPSAT-3A stereo pair was estimated as $58.68^{\circ}$. The investigation was assessed through the evaluation of the geopositioning analysis, image quality estimation and the accuracy of automatic Digital Surface Model (DSM) generation and compared with those of KOMPSAT-3 stereo pair with the convergence angle of $44.80^{\circ}$ over the same area. First, geopositioning accuracy was tested with initial rational polynomial coefficients (RPCs) and after compensating the biases of the initial RPCs by manually collected ground control points. Then, regarding image quality, relative edge response was estimated for manually selected points visible from two stereo pairs. Both of the initial and bias-compensated positioning accuracy and the quality assessment result expressed that KOMPSAT-3A images showed higher performance than those of KOMPSAT-3 images. Finally, the accuracy of DSMs generated from KOMPSAT-3A and KOMPSAT-3 stereo pairs were examined with respect to the reference LiDAR-derived DSM. The various DSMs were generated over the whole coverage of individual stereo pairs with different grid spacing and over three types of terrain; flat, mountainous and urban area. Root mean square errors of DSM from KOMPSAT-3A pair were larger than those for KOMPSAT-3. This seems due to larger convergence angle of the KOMPSAT-3A stereo pair.

• 전자공학회논문지
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• 제51권6호
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• pp.169-174
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• 2014

센서노드를 활용한 응용이 증가함에 따라 센서네트워크의 장기적 운용과 성능을 보장할 수 있는 현실적 배치 문제 해결 기법이 요구되고 있다. 특히 네트워크 연결성은 네트워크 전체 수명에도 영향을 줄 뿐만 아니라 근거리 센싱 정보의 취합 능력에도 직접적인 연관성을 갖는다. 센서네트워크의 구축 시 요구되는 경제적인 이유와 함께 센서 노드가 배치될 필드의 접근성 문제로 임의 배치 기법이 주로 사용되고 있으나 센서노드의 불균일로 인한 연결성 문제, 비효율적 네트워크 구성 등이 발생할 수 있다. 본 논문에서는 초기 배치 노드의 성능을 최대한 활용할 수 있도록 거점 노드의 혼합 배치 기법을 제안한다. 혼합 배치를 통해 기존 센서 노드의 불균형을 완화시키면서 추가되는 혼합 노드의 수를 효과적으로 줄일 수 있는 밀도 분석을 시행하였다. 실험 결과를 통하여 제안하는 기법이 단일 센서노드로 구성된 기존의 배치 방식 보다 좋은 결과를 얻을 수 있음을 보였다.

• 환경영향평가
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• 제15권2호
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• pp.121-127
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• 2006

The conventional water quality measurements by point sampling provide only site specific temporal water quality information but not the synoptic geographic coverage of water quality distribution. To circumvent these limitations in temporal and spatial measurements, the use of remote sensing is increasingly involved in the water quality monitoring research. In other to assess a trophic state of Yongdam reservoir using satellite imagery data, I obtained Landsat ETM data and water quality data on 16th September and 18th October 2001. The approach involved acquisition of water quality samples from boats at 33 sites on 16th September and 30 sites on 18th October 2001, simultaneous with Landsat-7 satellite overpass. The correlation coefficients between the DN values of the imagery and the concentrations of chlorophyll-a were analyzed. The visible bands(band 1,2,3) and near infrared band(band 4) data of September image showed the correlation coefficient values higher than 0.9. The October image showed the correlation coefficient values about 0.7 due to the atmospheric effect and low variation of chlorophyll-a concentration. Regression models between the chrophyll-a concentration and DN values of the Landsat imagery data have been developed for each image. The regression model was determined based on the spectral characteristics of chlorophyll, so the green band(band 2) and near infrared band(band 4) were selected to generate a trophic state map. The coefficient of determination(R2) of the regression model for 16th September was 0.95 and that of the regression model for 18th October was 0.55. According to the trophic state map made based on Aizaki's TSI and chlorophyll-a concentration, the trophic state of Yongdam reservoir was mostly eutrophic state during this study.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.556-559
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• 2007

The Urban Environmental Quality (UEQ) indicates a complex and various parameters resulting from both human and natural factors in an urban area. Vegetation, climate, air quality, and the urban infrastructure may interact to produce effects in an urban area. There are relationships among air pollution, vegetation, and degrading environmental the urban heat island (UHI) effect. This study investigates the application of multi-spectral remote sensing data from the Landsat ETM and TM sensors for the mapping of air quality and UHI intensity in Seoul from 2000 to 2006 in fine resolution (30m) using the emissivity-fusion method. The Haze Optimized Transform (HOT) correction approach has been adopted for atmospheric correction on all bands except thermal band. The general UHI values (${\Delta}(T_{urban}-T_{rural})$) are 8.45 (2000), 9.14 (2001), 8.61 (2002), and $8.41^{\circ}C$ (2006), respectively. Although the UHI values are similar during these years, the spatial coverage of "hot" surface temperature (>$24^{\circ}C$) significantly increased from 2000 to 2006 due to the rapid urban development. Furthermore, high correlations between vegetation index and land surface temperature were achieved with a correlation coefficients of 0.85 (2000), 0.81 (2001), 0.84(2002), and 0.89 (2006), respectively. Air quality is shown to be an important factor in the spatial variation of UEQ. Based on the quantifiable fine resolution satellite image parameters, UEQ can promote the understanding of the complex and dynamic factors controlling urban environment.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.82-84
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• 2003

Watershed boundaries and flow paths within the watershed are the most important factors required in watershed analysis. Most often the derivation of watershed boundaries and stream network and flow paths is based on topographical maps but spatial variation of flow direction is not clearly understandable using this method. Water resources projects currently use 1: 50, 000-scale ground survey or aerial photography-based topographical maps to derive watershed boundary and stream network. In basins, where these maps are not available or not accessible it creates a real barrier to watershed geo-spatial analysis. Such situations require the use of global datasets, like GTOPO30. Global data sets like ETOPO5, GTOPO30 are the only data sets, which can be used to derive basin boundaries and stream network and other terrain variations like slope aspects and flow direction and flow accumulation of the watershed in the absence of topographic maps. Approximately 1-km grid-based GTOPO 30 data sets can derive better outputs for larger basins, but they fail in flat areas like the Karkheh basin in Iran and the Amudarya in Uzbekistan. A new window in geo-spatial hydrology has opened after the launching of the space-borne satellite stereo pair of the Terra ASTER sensor. ASTER data sets are available at very low cost for most areas of the world and global coverage is expected within the next four years. The DEM generated from ASTER data has a reasonably good accuracy, which can be used effectively for hydrology application, even in small basins. This paper demonstrates the use of stereo pairs in the generation of ASTER DEMs, the application of ASTER DEM for watershed boundary delineation, sub-watershed delineation and explores the possibility of understanding the drainage flow paths in irrigation command areas. All the ASTER derived products were compared with GTOPO and 1:50,000-based topographic map products and this comparison showed that ASTER stereo pairs can derive very good data sets for all the basins with good spatial variation, which are equal in quality to 1:50,000 scale maps-based products.

• 한국정보과학회논문지:정보통신
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• 제29권2호
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• pp.141-155
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• 2002

본 논문에서는 기지국과 단말기간의 전파지연이 비교적 짧은 마이크로셀 환경의 패킷 CDMA망에서 음성과 데이타를 통합 서비스하기 위한 MAC 프로토콜을 제안한다. 제안한 프로토콜을 위한 시스템의 상향링크 채널은 프레임을 구성하는 타임 슬롯과 각 슬롯별 확산코드에 의하여 제공된다. 지연에 민감한 음성 트래픽에 더 높은 우선순위를 부여하여, 음성 트래픽인 경우에는 발음구간 동안 임의의 확산코드를 예약하여 서비스된다. 반면, 데이타 트래픽은 매 패킷이 발생할 때마다 기지국으로부터 수신한 현재 슬롯의 예약상태 정보를 기반으로 서비스된다. 성능분석의 결과, 본 논문에서 제안한 기법은 음성과 데이타 패킷간의 충돌이 전혀 발생하지 않으므로 주어진 패킷 누락률 범위 내에서 수용 가능한 최대 음성 단말기 수를 증가시킬 수 있었다.

• 대한원격탐사학회지
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• 제17권3호
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• pp.243-251
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• 2001

GPS(Global Positioning System)를 이용한 측위는 현재 가장 널리 쓰이는 측위 기법이다. 그러나 GPS 위치 측정시 일반 사용자는 전리층과 대류권의 영향으로 인해 항법이나 측위 등의 응용분야에서 만족할 만한 정확도를 얻을 수 없다. DGPS(Differential Global Positioning System)는 이러한 제약들을 해결할 수 있는 방법으로써, 이는 공통 오차를 제거하여 높은 정확도를 얻을 수 있다. 하지만 DGPS를 사용한 경우에도 정밀 측위에 있어서는 기준점으로부터의 거리 제한과 실시간 데이터 처리가 힘든 문제점을 내재하고 있다. 따라서 본 논문에서는 장기선 DGPS를 위한 실시간 보정신호 전송방법에 관하여 논한다. 이는 데이터 전송거리가 제한되는 종래의 무선 모뎀 방법에서의 문제를 해결하기 위하여 TCP와 UDP 또는 IP 프로토콜로 구성되는 TCP/IP 프로토콜 스택을 이용함으로써 어느 곳이나 RTK-GPS 위치 정보 데이터의 전송을 가능하게 한다.

• 한국전자파학회논문지
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• 제20권9호
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• pp.914-923
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• 2009

헬릭스 안테나는 관제, 관측, 탐사, 통신 위성 등에서 관제(TT&C), 데이터 통신, GPS 수신 시스템, 전술 시스템으로 활용되고 있다 위성의 Z축에서 최대 지향성과 방사 특성을 갖는 헬릭스는 광대역의 임피던스와 통신 커버리지 대역을 제공할 수 있다. 도파관 혼 구조는 흔히 레이다 분야에 이용되는데, 지반 탐사 레이다 및 전자파 장애 측정 등 초 광대역 펄스를 필요로 하는 곳에 사용된다. 또한 크기가 비교적 작고, 적은 방사 왜곡으로 인한 고효율과 낮은 반사 특성을 갖는 장점이 있다. 본 논문에서는 고용량의 데이터를 전송하여 넓은 주파수 대역폭을 사용하는 통신 및 원격 탐사 위성에 적합한 도파관 혼-헬릭스 결합 안테나를 설계한다. 설계된 변형 구조 안테나는 S 밴드에서 가변 빔 스캐닝 모드를 갖는 혼-헬릭스 결합 헬리콘 구조로 관제, 탐사, 고속 데이터 통신용 등의 다기능 안테나로 동작한다. 도파관 혼은 테이퍼된 헬릭스를 감싸는 접이식 반사체로 설계하여 구조물의 소형화를 유도한다. 현재 개발 중인 차세대 다목적 실용위성에서는 고성능의 탑재체를 활용하기 때문에 정밀하고 안정된 위성 자세 제어 능력을 요구하고, 위성 안테나의 지향성 요구 조건이 강화된다. 이를 위해 설계된 안테나의 위성 초기 배치에 따른 링크 분석을 통해 위성체의 자세 및 운용 모드에 따라 다른 결과를 갖는 빔 스캐닝을 산출하고 각 모드에서의 자료 전송률에 대해 연구한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권6호
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• pp.2689-2708
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• 2016

Multi-camera systems which integrate two or more low-cost digital cameras are adopted to reach higher ground coverage and improve the base-height ratio in low altitude remote sensing. To guarantee accurate multi-camera integration, the geometric relationship among cameras must be determined through platform calibration techniques. This paper proposed a combined two-step platform calibration method. In the first step, the static platform calibration was conducted based on the stable relative orientation constraint and convergent conditions among cameras in static environments. In the second step, a dynamic platform self-calibration approach was proposed based on not only tie points but also straight lines in order to correct the small change of the relative relationship among cameras during dynamic flight. Experiments based on the proposed two-step platform calibration method were carried out with terrestrial and aerial images from a multi-camera system combined with four consumer-grade digital cameras onboard an unmanned aerial vehicle. The experimental results have shown that the proposed platform calibration approach is able to compensate the varied relative relationship during flight, acquiring the mosaicing accuracy of virtual images smaller than 0.5pixel. The proposed approach can be extended for calibrating other low-cost multi-camera system without rigorously mechanical structure.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.7-10
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• 2005

Plant water deficiency during drought season causes physiological stress and can be a critical indicator of forest fire vulnerability. In this study, we attempt to analyze the spectral characteristics of water stressed vegetation by using the laboratory measurement on leaf samples and the canopy reflectance spectra extracted from satellite hyperspectral image data. Leaf-level reflectance spectra were measured by varying moisture content using a portable spectro-radiometer. Canopy reflectance spectra of sample forest stands of two primary species (pine and oak) located in central part of the Korean peninsula were extracted from EO-l Hyperion imaging spectrometer data obtained during the drought season in 2001 and the normal precipitation year in 2002. The preliminary analysis on the reflectance spectra shows that the spectral characteristics of leaf samples are not compatible with the ones obtained from canopy level. Although moisture content of vegetation can be influential to the radiant flux reflected from leaf-level, it may not be very straightforward to obtain the spectral characteristics that are directly related to the level of canopy moisture content. Canopy spectra form forest stands can be varied by structural variables (such as LAt, percent coverage, and biomass) other than canopy moisture content.