• Journal of Astronomy and Space Sciences
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• 제34권4호
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• pp.303-314
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• 2017

With increased human activity in space, the risk of re-entry and collision between space objects is constantly increasing. Hence, the need for space situational awareness (SSA) programs has been acknowledged by many experienced space agencies. Optical and radar sensors, which enable the surveillance and tracking of space objects, are the most important technical components of SSA systems. In particular, combinations of radar systems and optical sensor networks play an outstanding role in SSA programs. At present, Korea operates the optical wide field patrol network (OWL-Net), the only optical system for tracking space objects. However, due to their dependence on weather conditions and observation time, it is not reasonable to use optical systems alone for SSA initiatives, as they have limited operational availability. Therefore, the strategies for developing radar systems should be considered for an efficient SSA system using currently available technology. The purpose of this paper is to analyze the performance of a radar system in detecting and tracking space objects. With the radar system investigated, the minimum sensitivity is defined as detection of a $1-m^2$ radar cross section (RCS) at an altitude of 2,000 km, with operating frequencies in the L, S, C, X or Ku-band. The results of power budget analysis showed that the maximum detection range of 2,000 km, which includes the low earth orbit (LEO) environment, can be achieved with a transmission power of 900 kW, transmit and receive antenna gains of 40 dB and 43 dB, respectively, a pulse width of 2 ms, and a signal processing gain of 13.3 dB, at a frequency of 1.3 GHz. We defined the key parameters of the radar following a performance analysis of the system. This research can thus provide guidelines for the conceptual design of radar systems for national SSA initiatives.

• 한국전자통신학회논문지
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• 제13권4호
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• pp.787-794
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• 2018

지구 온난화로 인해 홍수나 집중 호우와 같은 자연 재해들이 증가하고 있다. 이러한 자연 재해들이 미리 그리고 효과적으로 인지될 수 있다면 재해로 인한 많은 피해들을 미리 막을 수 있을 것이다. 최근 비주얼 센서기술의 발전을 바탕으로 재해를 예방하기 위해 하천을 포함한 다양한 자연환경을 감시하는데 비주얼 센서 기술을 적용하는 연구들이 많이 진행되고 있다. 이 논문에서는 비주얼 센서 네트워크 기술을 이용한 하천 감시시스템에 적용 가능한 하천 영상에서 강물 영역을 분할하는 방법을 제안한다. 제안하는 방법에서는 먼저 최소 신장트리 알고리즘을 이용하여 영상을 세밀하게 분할한다. 그리고 강물 영역과 배경 영역에 대한 사전 정보를 이용하여 초기 영역을 설정하고 유사한 영역을 병합하여 각 영역을 확장함으로써 강물 영역을 분리한다. 실험결과는 제안하는 방법이 간단하면서도 정확하게 강물 영상에서 강물 영역을 분리하는 것을 보여준다.

• 정보처리학회논문지C
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• 제19C권3호
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• pp.209-214
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• 2012

시각 동기화는 무선 센서 네트워크에서 시각 정보가 활용되는 응용(예, 감시, 추적, 데이터 융합, 스케쥴링)에 있어서 중요하다. 무선 센서 네트워크에서의 시각 동기화는 기존의 유선 인터넷 망이나 다른 무선 통신망과도 다른 요구 사항을 만족해야 하는데, 이는 무선 센서 네트워크가 제한된 자원을 가지고 있기 때문이며, 그 중 특히 전력 소모가 가장 중요한 요소이다. 이 논문은 무선 센서 네트워크에서 동작하는 새로운 시각 동기화 방안에 관한 것으로 메시지 통신 부하를 줄여 결과적으로 전력 소모를 줄일 수 있다. 시뮬레이션 시험을 통해서 제안한 시각 동기화 방안이 기존의 방안보다 에너지 소모가 적으며 정확도가 향상되었음을 보인다.

• ETRI Journal
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• 제42권1호
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• pp.78-89
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• 2020

Human activity recognition (HAR) has become effective as a computer vision tool for video surveillance systems. In this paper, a novel biometric system that can detect human activities in 3D space is proposed. In order to implement HAR, joint angles obtained using an RGB-depth sensor are used as features. Because HAR is operated in the time domain, angle information is stored using the sliding kernel method. Haar-wavelet transform (HWT) is applied to preserve the information of the features before reducing the data dimension. Dimension reduction using an averaging algorithm is also applied to decrease the computational cost, which provides faster performance while maintaining high accuracy. Before the classification, a proposed thresholding method with inverse HWT is conducted to extract the final feature set. Finally, the K-nearest neighbor (k-NN) algorithm is used to recognize the activity with respect to the given data. The method compares favorably with the results using other machine learning algorithms.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.584-586
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• 2004

This paper deals with the development of on-line fault and lightning stroke section locating system for branched overhead transmission line. The section locating algorithm of this system i3 by analyzing the distribution pattern of current flowing through the overhead ground wire. It composes of three parts; current sensors, local remote terminal unit(RTU) and analysis program at surveillance tenter. Double Rogowski coil sensor having integrating amplifier was designed as current sensor. In order for current pattern analysis, the transmitted waves from each sensor wert synchronized by GPS tim c clock in RTU. While, lightning stroke location are judged only by polarity information of lightning currents. This design has a benefit in simplicity of signal processing unit of RTU.

• 대한전자공학회논문지TC
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• 제43권1호
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• pp.19-24
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• 2006

무선 센서 네트워크는 사람이 접근할 수 없는 곳에서 감시와 정보 수집과 같은 다양한 응용분야를 가진다. 무선 센서 네트워크의 주된 연구는 에너지 소모의 감소와 데이터의 신뢰성이다. 전방향 오류 정정(FEC)을 이용한 시스템은 FEC를 사용하지 않은 시스템 보다 적은 전송 전력으로 목표하는 데이터의 신뢰성을 제공한다. 본 논문에서는 무선 센서 네트워크를 위한 FEC로 다양한 부호율(0.53, 0.81, 0.91)을 가지는 LDPC부호의 사용을 제안한다. 또한 채널로 AWGN채널에 노드 간의 간섭을 고려한다. 제안한 시스템은 낮은 SNR에서 높은 신뢰도를 가지는 데이터 전송뿐만 아니라 데이터 전송 전력의 감소를 가진다.

• 한국컴퓨터정보학회논문지
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• 제22권7호
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• pp.101-108
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• 2017

A wireless image sensor node collecting image data for environmental monitoring or surveillance requires a large amount of energy to transmit the huge amount of video data. Even though solar energy can be used to overcome the energy constraint, since the collected energy is also limited, an efficient energy management scheme for transmitting a large amount of video data is needed. In this paper, we propose a method to reduce the number of blackout nodes and increase the amount of gathered data by selecting an appropriate video coding method according to the energy condition of the node in a solar-powered wireless video sensor network. This scheme allocates the amount of energy that can be used over time in order to seamlessly collect data regardless of night or day, and selects a high compression coding method when the allocated energy is large and a low compression coding when the quota is low. Thereby, it reduces the blackout of the relay node and increases the amount of data obtained at the sink node by allowing the data to be transmitted continuously. Also, if the energy is lower than operating normaly, the frame rate is adjusted to prevent the energy exhaustion of nodes. Simulation results show that the proposed scheme suppresses the energy exhaustion of the relay node and collects more data than other schemes.

• Smart Structures and Systems
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• 제1권4호
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• pp.325-338
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• 2005

Utilizing robotic based reconfigurable nodal structural health monitoring systems has many advantages over static or human positioned sensor systems. However, creating a robot capable of traversing a variety of civil infrastructures is a difficult task, as these structures each have unique features and characteristics posing a variety of challenges to the robot design. This paper outlines the design and implementation of a novel robotic platform for deployment on ferromagnetic structures as an enabling structural health monitoring technology. The key feature of this design is the utilization of an attachment device which is an advancement of the common magnetic base found in the machine tool industry. By mechanizing this switchable magnetic circuit and redesigning it for light weight and compactness, it becomes an extremely efficient and robust means of attachment for use in various robotic and structural health monitoring applications. The ability to engage and disengage the magnet as needed, the very low power required to do so, the variety of applicable geometric configurations, and the ability to hold indefinitely once engaged make this device ideally suited for numerous robotic and distributed sensor network applications. Presented here are examples of the mechanized variable force magnets, as well as a prototype robot which has been successfully deployed on a large construction site. Also presented are other applications and future directions of this technology.

• 한국군사과학기술학회지
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• 제19권1호
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• pp.66-75
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• 2016

Stereoscopic image generated by depth image-based rendering(DIBR) for surveillance robot and camera is appropriate in a low bandwidth network. The image is very important data for the decision-making of a commander and thus its integrity has to be guaranteed. One of the methods used to detect manipulation is to check if the stereoscopic image is taken from the original camera. Sensor pattern noise(SPN) used widely for camera identification cannot be directly applied to a stereoscopic image due to the stereo warping in DIBR. To solve this problem, we find out a shifted object in the stereoscopic image and relocate the object to its orignal location in the center image. Then the similarity between SPNs extracted from the stereoscopic image and the original camera is measured only for the object area. Thus we can determine the source of the camera that was used.

• 센서학회지
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• 제11권1호
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• pp.28-38
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• 2002

비디오 센서에 의한 감시 및 관측(VSAM)에 있어 사람은 중요하면서도 해석하기 어려운 목표이다. 본 논문에서는 연속 영상에서 자동으로 사람을 추적하거나 행위를 해석하는 작업에 선행하는 절차로서, 그 수를 계측하는 방법에 대해 다룬다. 정적인 비디오 카메라의 영상에서 사람만을 추출해낸 이진 영상을 얻고, 최상위 화소만을 연결한 선에서 지역최소점을 근거로 사람군을 나눈다. 이와 같이 나누어진 각 영역의 특성은 군내에서의 사람들의 상대적 위치에 따라 변화하게 되며, 이를 구분하기 위하여 완전 가림, 부분적 가림, 완전 분리된 개인, 오분리의 4가지 상태를 정의하였다. 연속적인 영상에서 나누어진 영역들의 상태가 변화하여가는 과정을 분석하여 관측 지역내 사람의 수를 추정하였으며, 이의 유용성을 실제 실험을 통하여 확인하였다.