• 한국농공학회논문집
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• 제61권3호
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• pp.1-14
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• 2019

North Korea has frequently suffered from extreme agricultural crop droughts, which have led to food shortages, according to the Food and Agriculture Organization (FAO). The increasing frequency of extreme droughts, due to global warming and climate change, has increased the importance of enhancing the national capacity for drought management. Historically, a meteorological drought index based on data collected from weather stations has been widely used. But it has limitations in terms of the distribution of weather stations and the spatial pattern of drought impacts. Satellite-based data can be obtained with the same accuracy and at regular intervals, and is useful for long-term change analysis and environmental monitoring and wide area access in time and space. The Evaporative Stress Index (ESI), a satellite-based drought index using the ratio of potential and actual evaporation, is being used to detect drought response as a index of the droughts occurring rapidly over short periods of time. It is more accurate and provides faster analysis of drought conditions compared to the Standardized Precipitation Index (SPI), and the Palmer Drought Severity Index (PDSI). In this study, we analyze drought events during 2015-2017 in North Korea using the ESI satellite-based drought index to determine drought response by comparing with it with the SPI and SPEI drought indices.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.118-121
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• 2006

Variations in the extent and dispersal of river plume are important in the study of coastal environment. The objectives of this study are to examine relationship between satellite detected plume area and river discharge and to clarify the temporal and spatial dynamic of plume from Tokachi River, Hokaido, Japan. We used 1.1 km spatial resolution of SeaWiFS normalized water-leaving radiance (nLw) images from 1998 to 2002. Supervised maximum likelihood classification was implemented to define classes of surface water optical properties. Satellite observed plume area was correlated to the amount of river discharge from April to October. First mode (44% of variance) of EOF analysis shows the turbid plume distribution resulting from re-suspension by strong wind mixing along the coast during winter. This mode also shows plume distribution along-shelf direction in spring and late summer. Second mode (17% of variance) shows spring pattern across-shelf direction due to strong discharge of snow melting water.

• 대한원격탐사학회지
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• 제28권6호
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• pp.683-691
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• 2012

High resolution satellite images are now widely used for a variety of mapping applications including photogrammetry, GIS data acquisition and visualization. As the spectral and spatial data size of satellite images increases, a greater processing power is needed to process the images. The solution of these problems is parallel systems. Parallel processing techniques have been developed for improving the performance of image processing along with the development of the computational power. However, conventional CPU-based parallel computing is often not good enough for the demand for computational speed to process the images. The GPU is a good candidate to achieve this goal. Recently GPUs are used in the field of highly complex processing including many loop operations such as mathematical transforms, ray tracing. In this study we proposed a technique for parallel processing of high resolution satellite images using GPU. We implemented a spectral radiometric processing algorithm on Landsat-7 ETM+ imagery using CUDA, a parallel computing architecture developed by NVIDIA for GPU. Also performance of the algorithm on GPU and CPU is compared.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권9호
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• pp.3152-3171
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• 2022

This work investigates the physical layer secrecy of a multi-antenna hybrid satellite-terrestrial relay networks (HSTRN) with jamming, in which a satellite aims to make communication with a destination user by means of a relay, along with spatially random eavesdroppers. In order to weaken the signals of eavesdroppers, the conventional relay can also generate intentional interference, besides forwarding the received signal. Shadowed-Rician fading is adopted in satellite link, while Rayleigh fading is adopted in terrestrial link, eavesdropper link and jamming link. The analytical and asymptotic formulas for the system secrecy outage probability (SOP) are characterized. Practical insights on the diversity order of the network are revealed according to the asymptotic behavior of SOP at high signal-to-noise ratio (SNR) regime. Then, analysis of the system throughput is examined to assess the secrecy performance. In the end, numerical simulation results are presented to validate the theoretical analysis and point out: (1) The secrecy performance of the considered network is affected by the channel fading scenario, the system configuration; (2) Decrease of the relay coverage airspace can provide better SOP performance; (3) Jamming from the relay can improve secrecy performance without additional network resources.

• 한국대기환경학회지
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• 제23권6호
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• pp.653-665
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• 2007

Several numerical experiments were carried out to clarify the influence of satellite data assimilation with various spatial resolution on mesoscale meteorological wind and temperature field. Satellite data used in this study is QuikSCAT launched on ADEOS II. QuikSCAT data is reasonable and faithful sea wind data, which have been verified through many observational studies. And numerical model in the study is MM5 developed by NCAR. Difference of wind pattern with and without satellite data assimilation appeared clearly, especially wind speed dramatically reduced on East Sea, when satellite data assimilation worked. And sea breeze is stronger in numerical experiments with RDAPS and satellite data assimilation than that with CDAS and data assimilation. This caused the lower estimated surface temperature in CDAS used cases. Therefore the influence of satellite data assimilation acts differently according to initial data quality. And it is necessary to make attention careful to handle the initial data for numerical simulations.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.644-648
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• 2002

Though it was difficult of globally monitor latent heat flux aver the ocean for many years, the situation is rapidly changing by the use of satellite data. Since a bulk formula is used to estimate turbulent heat flux using satellite data, we need wind speed, sea surface temperature and specific humidity data. However, it is not easy to accurately estimate specific humidity using satellite data. Now several algorithms for estimating specific humidity have been proposed and applied to construct latent heat flux data sets. Latent heat flux data sets derived from satellite data such as J-OFURO, HOAPS and GSSTF are available at present. Since the algorithm and used satellite data are not the same between them. the characteristics of each data set may be different. Therefore, it is important to clarify the difference between each data set and investigate the cause of the difference in latent heat flux estimates. In this paper we summarize the present state of the art with regard to the turbulent heat flux estimation by using satellite data. Also we present the comparison results of latent heat flux fields including not only satellite-derived flux fields but also analysis fields.

• 인터넷정보학회논문지
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• 제21권6호
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• pp.1-12
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• 2020

저궤도 위성을 활용한 모바일 위성 네트워크는 낮은 출력의 소형화된 단말기를 통해 서비스를 제공할 수 있어 국가 공공재난망 및 국방분야 등 기반 통신망을 사용하기 어려운 상황에서 신뢰성 있는 통신수단으로 활용될 수 있다. 그러나 비상대비 상황에서의 High Traffic 환경은 위성 네트워크의 New call blocking 확률과 Handover Failure 확률을 높이며, 저궤도 위성은 매우 빠른 속도로 궤도를 이동하므로 Handover Failure 확률 증가는 서비스 품질에 큰 영향을 미친다. 위성통신의 채널 할당방식 중 FCA 방식은 DCA에 비해 높은 트래픽에서 상대적으로 양호한 성능을 보여 비상대비 상황에 적절하나 트래픽 증가 시 QoS를 최적화하기 위해 New call blocking 확률과 Handover failure 확률을 최소화해야 한다. 본 논문에서는 FCA 방식 중 Handover Call에 우선권을 부여하는 FCA-QH 방식을 예시로 하여 저궤도 위성의 빔폭과 터미널들의 통화시간을 적응적으로 조절하여 QoS를 개선하는 LEO-DBC(LEO satellite Dynamic Beam width Control) 기법을 제안한다. LEO-DBC 기법을 통해 비상대비 상황의 High traffic 환경에서 모바일 위성통신 네트워크의 QoS를 최적으로 유지할 수 있을 것으로 기대한다.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제28권6호
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• pp.472-479
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• 2002

Since $Br^{\circ}anemark$ introduced the osseointegrated implants, they have been granted for useful methods for the restoration of oral function. The original $Br^{\circ}anemark$ protocol recommended long stress-free healing periods to achieve the osseointegration of dental implants. However, many clinical and experimental studies have shown that the osseointegration is no wonder in almost cases and that early and immediate loading may lead to predictable osseointegration. So we are willing to introduce the Satellite Abutment newly invented for immediate loading. We think that it will make the occlusal forces dispersed to surrounding bone and that we can restore the oral function immediately after implant installation not disturbing osseointegration. In case of using Satellite abutment, stress concentrated to bone contact area of implant was distributed not only fixation plate and screws but also superior, middle portion of implant and cortical layer of jaw bone. It was clearly decreased on the bone contact surfaces around dental implants. 1. Stress was decreased more than 76.5% when satellite straight abutment was used. 2. Stress was decreased more than 50% when satellite angled abutment was used. 3. The stress around dental implant was well distributed along the cortical bone surface and the fixation plate and screw. This study concludes that satellite abutment can be used as all immediate loading implant prothesis because it was possible to distribute periimplant occlusal stress through implant contact bone surface and cortical layer of jaw bone.

• 한국지리정보학회지
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• 제23권3호
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• pp.236-251
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• 2020

원격탐사 기술의 발전과 활용 가능한 위성의 증가로 재난의 예방, 대비, 대응, 복구 등에서 위성영상자료의 활용에 대한 요구가 높아지고 있다. 위성영상은 센서의 특성에 따라 적용 가능한 재난의 모니터링을 위해 활용되고 있지만, 통합된 모니터링 시스템의 구축을 위해 기존 시스템을 평가하고 이를 바탕으로 실현 가능한 준실시간 통합 재난모니터링 시스템 구축을 위한 구체적인 청사진을 제시한 연구는 국내뿐만 아니라 국외에서도 그 사례가 확인되지 않는다. 본 연구는 원격탐사를 통한 재난모니터링의 개념화를 통해 준실시간 재난모니터링 시스템 구축의 장애요인들을 확인하고, 실제로 활용 가능한 영상자료와 실현 가능한 재난모니터링 시스템을 제시하였다. 원격탐사를 통한 준실시간 재난모니터링은 다양한 요인들에 의해 통합시스템의 구축이 제한되며, 시스템 구축을 위한 기술적, 경제적 요인과 함께 위성영상 확보의 적시성을 가로막는 정책적 요인과 일관성 있는 정보생산을 위한 영상분석에 대한 제도적 요인에도 크게 영향을 받는 것으로 나타났다. 이러한 제약들은 AWS(Amazon Web Services)와 같은 위성영상의 저장, 취득, 분석에 활용되는 컴퓨팅 플랫폼과 같은 통합서버의 확보와, 재난의 종류와 상황에 부합하는 활용 가능 위성의 궤도분석을 가능하게 하는 분석도구의 개발에 의해 극복될 수 있을 것으로 판단된다. 본 연구는 이러한 제도적, 경제적, 기술적, 정책적 제약들을 극복할 수 있는 위성영상 기반 통합 재난모니터링 시스템 구축을 위한 프레임워크를 제시하였으며, 재난의 종류와 단계에 따른 AI 기반 위성영상 분석 방법론을 제안하였다. 이러한 결과는 원격탐사와 재난관리 분야에 학술적 시사점을 제공하고, 재난모니터링 분야에 실무적 기여를 할 것으로 판단된다.

• ETRI Journal
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• 제22권4호
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• pp.40-50
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• 2000

We apply a "sliding-window" Maximum Likelihood(ML) estimator to estimate traffic parameters On-Off source and develop a method for estimating stochastic predicted individual cell arrival rates. Based on these results, we propose a simple Connection Admission Control(CAC)scheme for delay sensitive services in broadband onboard packet switching satellite systems. The algorithms are motivated by the limited onboard satellite buffer, the large propagation delay, and low computational capabilities inherent in satellite communication systems. We develop an algorithm using the predicted individual cell loss ratio instead of using steady state cell loss ratios. We demonstrate the CAC benefits of this approach over using steady state cell loss ratios as well as predicted total cell loss ratios. We also derive the predictive saturation probability and the predictive cell loss ratio and use them to control the total number of connections. Predictive congestion control mechanisms allow a satellite network to operate in the optimum region of low delay and high throughput. This is different from the traditional reactive congestion control mechanism that allows the network to recover from the congested state. Numerical and simulation results obtained suggest that the proposed predictive scheme is a promising approach for real time CAC.