• 한국음향학회지
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• 제29권3호
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• pp.155-164
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• 2010

본 논문에서는 두 개의 항적 센서를 이용한 수상함 항적 탐색 방법을 제안한다. 수상함의 항적은 수상함 후면의 수면 위에 그 이동 자취에 따라 생성된다. 본 논문에서는 항적 반향 강도가 수상함에 가까울수록 강하며 항적 탐지 센서는 항적 반향 강도를 탐지할 수 있다는 가정 아래, 항적 반향 강도를 이용한 효과적인 항적 탐색 방법을 제안하였다. 제안한 탐색 방법의 성능 평가를 위해 몬테카를로 시뮬레이션을 적용하였으며, 실험 결과 제안한 탐색 방법이 기존의 단일 항적 센서를 이용한 탐색 방법에 비해 평균 탐색 시간 측면에서 약 45초 정도의 성능 향상을 나타내었다. 또한, 항적 길이가 짧은 경우에 본 논문에서 제안한 탐색 방법이 기존의 방법에 비해 효율적임을 알 수 있었다.

• 대한기계학회논문집B
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• 제28권2호
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• pp.181-188
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• 2004

The frequency characteristics in an axial flow fan operating at a design and three off-design operating conditions have been investigated by measuring the velocity fluctuation of a tip leakage vortex and a wake flow. Two hot-wire probe sensors rotating with the fan rotor. a fixed and a moving ones, were introduced to obtain a cross-correlation coefficient between two sensors as well as the fluctuating velocity. The results show that the spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region of higher flow rates than those in the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition. Detailed wake flow just downstream of the rotor blade was also measured by the rotating hot-wire sensor. The peak frequency of a high velocity fluctuation due to Karman vortex shedding in the wake region is mainly observed at the higher flow rate condition than that in the design point.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2010년도 한국컴퓨터종합학술대회논문집 Vol.37 No.1(D)
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• pp.360-365
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• 2010

In this paper, we present a distributed algorithm for detecting dynamic event regions in wireless sensor network with the consideration on energy saving. Our model is that the sensing field is monitored by a large number of randomly distributed sensors with low-power battery and limited functionality, and that the event region is dynamic with motion or changing the shape. At any time that the event happens, we need some sensors awake to detect it and to wake up its k-hop neighbors to detect further events. Scheduling for the network to save the total power-cost or to maximize the monitoring time has been studied extensively. Our scheme is that some predetermined sensors, called critical sensors are awake all the time and when the event is detected by a critical sensor the sensor broadcasts to the neighbors to check their sensing area. Then the neighbors check their area and decide whether they wake up or remain in sleeping mode with certain criteria. Our algorithm uses only 2 bit of information in communication between sensors, thus the total communication cost is low, and the speed of detecting all event region is high. We adapt two kinds of measure for the wake-up decision. With suitable threshold values, our algorithm can be applied for many applications and for the trade-off between energy saving and the efficiency of event detection.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
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• pp.946-949
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• 2006

With repeated coverage, spaceborne SAR (Synthetic Aperture Radar) instruments provide the most efficient means to monitor and study the changes in important elements of the marine environment. Due to highresolution of SAR data, the coverage of SAR sensor is always limited, especially for a repeat cycle. With more SAR sensors from various satellites, new data products such as ocean surface drift can be derived when two SARs' tracks overlap in a short time over coastal areas. Currently, there are two SAR sensors on different satellites with almost the exactly same path. That is, ERS-2 is following ENVISAT with a 30-minutes delay, which will be a good timing for ocean mesosclae feature tracking. For another application, a mystery ship near a big eddy with strong ship wake has been tracked between ERS-2 and ENVISAT SAR images to estimate its ship speed.

• 한국IT서비스학회지
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• 제15권4호
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• pp.97-109
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• 2016

The rapid deployment of millions of mobile sensors and smart devices has resulted in high demand for opportunistic encounter-based networking. For the cooperative video surveillance of dashboard cameras in nearby vehicles, a fast and energy-efficient asynchronous neighbor discovery protocol is indispensable because a dashboard camera is an energy-hungry device after the vehicle's engine has turned off. In the existing asynchronous neighbor discovery protocols, all nodes always try to discover all neighbors. However, a dashboard camera needs to discover nearby dashboard cameras when an event is detected. In this paper, we propose a fast and energy-efficient asynchronous neighbor discovery protocol, which enables nodes : 1) to have different roles in neighbor discovery, 2) to discover neighbors within a search range, and 3) to report promptly the exact discovery result. The proposed protocol has two modes: periodic wake-up mode and active discovery mode. A node begins with the periodic wake-up mode to be discovered by other nodes, switches to the active discovery mode on receiving a neighbor discovery request, and returns to the periodic wake-up mode when the active discovery mode finishes. In the periodic wake-up mode, a node wakes up at multiples of number ${\alpha}$, where ${\alpha}$ is determined by the node's remaining battery power. In the active discovery mode, a node wakes up for consecutive ${\gamma}$ slots. Then, the node operating in the active discovery mode can discover all neighbors waking up at multiples of ${\beta}$ for ${\beta}{\leq}{\gamma}$ within ${\gamma}$ time slots. Since the proposed protocol assigns one half of the duty cycle to each mode, it consumes equal to or less energy than the existing protocols. A performance comparison shows that the proposed protocol outperforms the existing protocols in terms of discovery latency and energy consumption, where the frequency of neighbor discovery requests by car accidents is not constantly high.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2004년도 Proceedings of ISRS 2004
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• pp.144-147
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• 2004

Two different sensors (here, KOMPSAT and RADARSAT) are considered for ship detection, and are used to delineate the detection performance for their data. The experiments are set for coastal regions of Mokpo Port and Ulsan Port and field experiments on board pilot boat are conducted to collect in situ ship validation information such as ship type and length. This paper introduce mainly the experiment result of ship detection by both RADARSAT SAR imagery and landbased RADAR data, operated by the local Authority of South Korea, so called vessel traffic system (VTS) radar. Fine imagery of Ulsan Port was acquired on June 19, 2004 and in-situ data such as wind speed and direction, taking pictures of ships and natural features were obtained aboard a pilot ship. North winds, with a maximum speed of 3.1 m/s were recorded. Ship's position, size and shape and natural features of breakwaters, oil pipeline and alongside ship were compared using SAR and VTS. It is shown that KOMPSAT/EOC has a good performance in the detection of a moving ship at a speed of 7 kts or more an hour that ship and its wake can be imaged. The detection capability of RADARSAT doesn't matter how fast ship is running and depends on a ship itself, e.g. its material, length and type. Our results indicate that SAR can be applicable to automated ship detection for a VTS and SAR combination service.

• 한국통신학회논문지
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• 제41권11호
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• pp.1574-1579
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• 2016

본 논문은 무인항공기 비행시간 향상을 위해 RF 무선 전력 획득 기술을 이용한 self-powered 센서 노드 회로에 관해 설계 연구하였다. 제안하는 센서 노드는 두 가지 경우가 만족하였을 때 동작한다. 마스터 노드의 입력 RF ID와 센서 노드의 ID가 같을 경우와 RF 무선 전력 획득 시스템이 히스테리시스 스위치에 의해 동작될 때다. 마스터 노드의 출력은 263 MHz에서 26 dBm을 사용하였다. RF 전력을 DC 전력으로 변환하는 최대 효율은 마스터 노드에서 2미터 떨어진 지점(4-6 dBm)에서 55 %이다. 최대 RF 무선 전력 획득 범위는 마스터 노드와 센서 노드의 거리가 약 13 m 이다. 센서 노드의 MCU 및 수신기와 온도 센서와 같은 부하의 소비 전력은 10 msec 동안 5.0 V에서 평균 15 mA이다.

• 대한기계학회논문집
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• 제16권5호
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• pp.924-932
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• 1992

본 연구에서는 풍동내에 놓여진 탄성지지 실린더의 와유출 특성과 진동 응답 을 동시에 측정하고 분석하여 유입속도 변화에 따른 이들의 상호관계를 확인하고 아울 러 실린더가 통과하는 풍동측정부에 있는 틈새 간격변화가 와유출과 실린더의 진동특 성에 미치는 영향에 대해 조사하였다.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2004년도 추계학술발표회
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• pp.43-47
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• 2004

두 개의 다른 위성 센서 (RADARSATSAR와 KOMPSAT EOC)를 사용하여 선박탐지 실험을 실시하였으며, 탐지성능을 검토하였다. 목포항과 울산항을 대상으로 실시하였으며 필요에 따라 현장 검증 데이터를 얻기 위하여 위성 통과 시에 선박에 승선하여 선박정보를 포함하는 Sea Truth를 취득하였다. 또한 VTS레이더 정보를 위성데이터와 비교를 통하여 위치정보의 검증을 수행하였다. 광학과 마이크로파 원격탐사에 있어 그 특성의 차이는 뚜렷하였으나, 광학의 경우 선속 3.1kts 이상인 선박의 후류가 탐지되었으며, 마이크로파의 경우, 최대 6-7kts의 선박에 대해서도 후류의 탐지는 어려웠다. 그러나, 마이크로파는 다양한 선형을 반영한 신호가 sigma nought로 표현되므로 향후 선형 정보뿐만 아니라, 침로의 추출이 가능하다는 결론을 얻었다. 또한, 동일 선박이라 할지라도 신호강도의 차이에 의해 선박이 2개 이상으로 나타나는 현상도 파악되었다. 앞으로 다양한 해상환경 및 위성 관측 모드에 따른 추가 실험을 실시하여 자동 선박추출이 가능할 것으로 판단된다.