• Ocean and Polar Research
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• 제35권4호
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• pp.291-298
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• 2013

In order to investigate the topography and exposure duration of the Siheung tidal flat, tidal ranges and DEM constructed by remote sensing techniques were analyzed. A cross-sectional diagram of the intertidal area reveals that it is relatively flat in the upper zone and then abruptly plunges into the bottom of the main channel where elevations increase in an upstream direction. The waterline during the Highest Low Water (HLW) is drawn back to the bottom of the channel at the middle part of the tidal flat and is formed along the slant of the channel during the Lowest High Water (LHW). The intertidal zone is located between -410 cm and 510 cm in terms of elevation and its total area is $0.65km^2$. An area between the Highest High Water (HHW) and Lowest High Water (LHW), occupying about 80% of the total area, occupies $0.52km^2$ of total area and accounts for 56% of the exposure duration. The boundary of wetland protection area in the Siheung tidal flat did not exactly coincide with the intertidal regime and differs by more than 15%. This study, which precisely analyzed the tidal flat area, tidal environment, and topography, would be useful in making a conservation plan and in learning how to use a wetland protection area in a sustainable manner.

• 센서학회지
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• 제25권5호
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• pp.344-348
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• 2016

We developed a 2-channel fiber-optic temperature sensor (FOTS) using a temperature sensing probe, a fiber-optic coupler, transmitting optical fiber, and an optical time domain reflectometer (OTDR). The temperature sensing probe is divided into a sensing probe and a reference probe for accurate thermometry. A sensing probe is composed of a silicon oil, a FC terminator, a brass pipe, and a singlemode optical fiber and the structure of a reference probe is identical with that of the sensing probe excluding a silicon oil. In this study, we measured the modified optical powers of the light signals reflected from the temperature sensing probe placed inside of the water with a thermal variation from 5 to $70^{\circ}C$. Although the optical power of the reference probe was constant regardless of the temperature change, the optical power of the sensing probe decreased linearly as the temperature increased. As experimental results, the FOTS using a subtraction method showed a small difference (i.e., hysteresis) in its response due to heating and cooling. The reversibility and reproducibility of the FOTS were also evaluated.

• 한국위성정보통신학회논문지
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• 제6권2호
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• pp.72-77
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• 2011

스펙트럼 센싱은 인지무선통신(CR, Cognitive Radio) 네트워크를 구성함에 있어 핵심적인 기술 중에 하나이다. 2차 사용자인 CR사용자는 1차 사용자에게 간섭을 주지 않기 위해 스펙트럼을 센싱 하여 해당 채널이 비어있거나 규정된 레벨 이하일 경우에만 해당 채널을 사용하게 된다. 최근 스마트폰의 사용으로 데이터의 트래픽이 증가함에 따라 광대역 서비스가 급증하고 있으며, 그에 따라 한 번에 넓은 대역을 센싱하는 광대역 센싱 기법의 필요성이 점차 높아지고 있다. 이러한 광대역 센싱은 인지무선통신이 수행되기 위한 매우 중요한 기술 중 하나이다. 높은 분해능을 갖는 광대역 센싱을 수행하기 위해서는 신뢰 할 수 있는 신호를 얻기 위한 알고리즘 처리가 선행되어야 한다. 따라서, 본 논문에서는 채널 상태가 좋지 않은 부 대역을 제외한 나머지 대역을 CR 사용자가 각각 센싱하여 정보를 취합하여 1차 사용자의 유무를 결정하는 협력 센싱 기법을 제안하였다. 이 때, 신호의 신뢰성을 높이기 위해 각각의 부 대역으로 나눈 CSI(Channel State Information)를 이용하여, 채널 상태를 파악한다. 또한, 검출 기법으로는 시스템 복잡도를 감소시키기 위하여 에너지검출 기법을 사용한다. 모의실험을 통해 성능을 검증하였고 그 성능은 SNR(Signal Noise ratio)에 따른 검출 확률로 나타내었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.434.2-434.2
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• 2014

We observe enhanced pH response of solution-gated field-effect transistors (SG-FET) having 1D-2D hybrid channel of vertical grown ZnO nanorods grown on CVD graphene (Gr). In recent years, SG-FET based on Gr has received a lot of attention for biochemical sensing applications, because Gr has outstanding properties such as high sensitivity, low detection limit, label-free electrical detection, and so on. However, low-defect CVD Gr has hardly pH responsive due to lack of hydroxyl group on Gr surface. On the other hand, ZnO, consists of stable wurtzite structure, has attracted much interest due to its unique properties and wide range of applications in optoelectronics, biosensors, medical sciences, etc. Especially, ZnO were easily grown as vertical nanorods by hydrothermal method and ZnO nanostructures have higher sensitivity to environments than planar structures due to plentiful hydroxyl group on their surface. We prepared for ZnO nanorods vertically grown on CVD Gr (ZnO nanorods/Gr hybrid channel) and to fabricate SG-FET subsequently. We have analyzed hybrid channel FETs showing transfer characteristics similar to that of pristine Gr FETs and charge neutrality point (CNP) shifts along proton concentration in solution, which can determine pH level of solution. Hybrid channel SG-FET sensors led to increase in pH sensitivity up to 500%, compared to pristine Gr SG-FET sensors. We confirmed plentiful hydroxyl groups on ZnO nanorod surface interact with protons in solution, which causes shifts of CNP. The morphology and electrical characteristics of hybrid channel SG-FET were characterized by FE-SEM and semiconductor parameter analyzer, respectively. Sensitivity and sensing mechanism of ZnO nanorods/Gr hybrid channel FET will be discussed in detail.

• 반도체디스플레이기술학회지
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• 제15권2호
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• pp.55-60
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• 2016

This study was developed through the secondary battery module charging/discharger possible utilization in the production process equipment circuit. The developed module is ensuring construction of efficient and productive charging and discharger through this research a limit on the yield and the price of existing single -channel charge and discharger circuit as a 5V 70A grade secondary battery Formation charge and discharger for up to 1 board 4 channels. In order to improve the sensing accuracy, through a robust differential amplifier circuit described using 16bit Analog-Digital Converter and noise was secured 16bit resolution sensing. The configuration also made demands for property Rise / Fall Time. Data Acquisition, discharge efficiency and also to fit the sink circuit temperature level for mass production.

• Journal of Communications and Networks
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• 제11권2호
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• pp.134-147
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• 2009

Tracking and exploiting instantaneous spectrum opportunities are fundamental challenges in opportunistic spectrum access (OSA) in presence of the bursty traffic of primary users and the limited spectrum sensing capability of secondary users. In order to take advantage of the history of spectrum sensing and access decisions, a sequential decision framework is widely used to design optimal policies. However, many existing schemes, based on a partially observed Markov decision process (POMDP) framework, reveal that optimal policies are non-stationary in nature which renders them difficult to calculate and implement. Therefore, this work pursues stationary OSA policies, which are thereby efficient yet low-complexity, while still incorporating many practical factors, such as spectrum sensing errors and a priori unknown statistical spectrum knowledge. First, with an approximation on channel evolution, OSA is formulated in a multi-armed bandit (MAB) framework. As a result, the optimal policy is specified by the wellknown Gittins index rule, where the channel with the largest Gittins index is always selected. Then, closed-form formulas are derived for the Gittins indices with tunable approximation, and the design of a reinforcement learning algorithm is presented for calculating the Gittins indices, depending on whether the Markovian channel parameters are available a priori or not. Finally, the superiority of the scheme is presented via extensive experiments compared to other existing schemes in terms of the quality of policies and optimality.

• 한국인터넷방송통신학회논문지
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• 제13권6호
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• pp.93-99
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• 2013

제안하는 프로토콜은 기존의 검출 기법에 비해 더 높은 성능을 얻을 수 있을 뿐만 아니라 검출 결과의 수를 줄임으로서 네트워크 자원을 절약할 수 있다. 레일리 페이딩 채널 상에서 협력 스펙트럼 검출은 많은 수의 2차 사용자를 필요로 한다. 이러한 2차 사용자들은 1차 사용자의 신호를 검출한다. 본 논문에서 제안하는 협력 스펙트럼 검출은 가장 높은 전력의 1차 사용자 신호를 수신한 단 하나의 2차 사용자만이 검출 결과를 전송하고 나머지 2차 사용자들은 중계기로서 공동 수신단으로 전송을 돕는 역할을 한다.

• Journal of electromagnetic engineering and science
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• 제12권2호
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• pp.148-154
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• 2012

In this paper, we propose an algorithm to conserve resources of the common control channel in a cognitive radio network by rejecting the redundant users using cooperative spectrum sensing. The proposed scheme is investigated under the paradigm of active spectrum sensing and a sequential detection technique. The algorithm is based on the J-divergence between the hypotheses of non primary user operation and the otherwise case. We select the most significant eigenvalues, which primarily affect the global statistical test. For the case where interference is from a secondary system transmission, a match filter is first employed to remove the degradation, and then the proposed algorithm is employed to remove the cooperative sensing nodes. Numerical results are provided and compared with conventional cases in order to validate the performance of the proposed algorithm.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
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• pp.864-867
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• 2006

Thermal infrared images of Landsat-5 TM and Landsat-7 ETM+ sensors have been unrivalled sources of high resolution thermal remote sensing (60m for ETM+, 120m for TM) for more than two decades. Atmospheric effect that degrades the accuracy of Sea Surface Temperature (SST) measurement significantly, however, can not be corrected as the sensors have only one thermal channel. Recently, MODIS sensor onboard Terra satellite is equipped with dual-thermal channels (31 and 32) of which the difference of at-satellite brightness temperature can provide atmospheric correction with 1km resolution. In this study we corrected the atmospheric effect of Landsat SST by using MODIS data obtained almost simultaneously. As a case study, we produced the Landsat SST near the eastern and western coast of Korea. Then we have obtained Terra/MODIS image of the same area taken approximately 30 minutes later. Atmospheric correction term was calculated by the difference between the MODIS SST (Level 2) and the SST calculated from a single channel (31 of Level 1B). This term with 1km resolution was used for Landsat SST atmospheric correction. Comparison of in situ SST measurements and the corrected Landsat SSTs has shown a significant improvement in $R^2$ from 0.6229 to 0.7779. It is shown that the combination of the high resolution Landsat SST and the Terra/MODIS atmospheric correction can be a routine data production scheme for the thermal remote sensing of ocean.

• 대한원격탐사학회지
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• 제23권2호
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• pp.131-135
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• 2007

조간대의 조류로 발달은 조간대 퇴적물종류, 입도, 조성 및 조류의 세기 등 에 많은 영향을 받는다. 따라서 조류로의 발달 특성, 밀도, 형태 등은 조간대의 특징을 분석하는데 활용될 수 있다. 그러나 아직 갯벌의 조류로에 대한 정량적 분석은 매우 미흡한 실정이다. 이 연구에서는 조류로의 정량적 분류기준으로 프랙탈 분석방법을 제시하고, 발달 정도가 다른 두 지역의 조류로에 대한 적용결과에 대한 정량적 비교를 제시한다. 시험 적용지역인 강화도 남단 조간대에서 얻어진 IKONOS 영상으로부터 조류로를 추출한 뒤, 프랙탈 분석방법 중 2차원 분석에 많이 사용되는 box counting 방법을 적용하여 프랙탈 차원을 구하였다. 분석 결과 강화도 남단 전체 조간대 지역에 대한 프랙탈 차원 값은 약 1.31로 나타났다. 조류로의 지선이 단순하며 남북으로 수직방향으로 발달한 지역은 프랙탈 차원 값이 $1.0563\sim1.0672$로 비교적 적은 값을 나타내는 반면, 조류로의 지선이 발달하고 매우 복잡한 형태를 보이는 곳은 프랙탈 차원 값이 $1.2550\sim1.3016$로 나타났다. 즉, 조류로의 발달정도에 따라 프랙탈 차원 값이 약 0.2 정도로 매우 뚜렷한 차이를 나타내며, 따라서 조류로의 정량적 구분이 프랙탈 분석에 의하여 가능하다는 결론을 얻을 수 있다. 향후 다른 특성을 갖는 다양한 조간대 지역에 적용하면 조류로의 발달정도와 환경 인자에 대한 정량적 분석이 가능할 것으로 사료된다.