• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.25-31
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• 2011

In the underwater communications, transmitted acoustic signal is corrupted by interference from multipath. A parametric array transducer is capable of radiating a narrow beam with very low sidelobe levels. In certain cases, the parametric array transducer can help the multipath problem. To improve the performance of the underwater communications, the statistical signal processing methods will be required. In the paper, the communication system using a parametric array transducer was demonstrated. To detect the received signal of the communication system based on the on-off keying, the maximum likelihood method using averaged signal for a particular window size is used. The communication system has GUI using LebVIEW which allows the user to change the parameter. The GUI can also be easily modified based on the characteristics of a parametric array transducer. The implemented system can effectively evaluate the performance of the parametric array transducer.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.48 no.6
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• pp.97-108
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• 2011

Systems for underwater environment monitoring and natural resources can be considered as a part of digital convergence where real-time data transmission is possible with the help of underwater wireless sensor network (UWSN). One of key technologies required for the deployment of the systems is underwater acoustic micro modem. In this work, we design and implement an acoustic modem equipped with a commercial omnidirectional transducer. We also make experiments at the northern Han river for the verification of the developed modem. According to the experiments, the modem supports the working distance of 250 m and the data rate of 200 bps with a negligible bit error rate. It is expected that the acoustic modem can be used for various applications based on UWSN in a near future.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.39 no.3
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• pp.44-52
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• 2002

In this paper, we present an analytical method for decision boundary feature extraction for neural networks. It has been shown that all the features necessary to achieve the same classification accuracy xxxas in the original space can be obtained from the vectors normal to decision boundaries. However, the vector normal to the decision boundary of a neural network has been calculated numerically using a gradient approximation. This process is time-consuming and the normal vector may be inaccurately estimated. In this paper, we propose a method to improve the performance of the previous decision boundary feature extraction for neural networks by accurately calculating the normal vector When the normal vectors are computed analytically, it is possible to reduce the processing time significantly and improve the performance of the previous implementation that employs numerical approximation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.12
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• pp.54-61
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• 2011

We propose a surveillance-alert system based on optimal placements of PDR(Pulsed Doppler Radar) sensors in USN. By using the detection information of moving target from PDR sensor and by considering the covered detection region and geographical property of the strategic area, three optimal placements of sensors are proposed. The proposed placement are named as the grid type, the linear type and the zigzag type. Also, the surveillance alert system based on three sensor placements are developed. The alert level of the proposed surveillance-alert system are 'Perception', 'Caution', 'Warning' and 'Danger' which are decided by the distance change between the moving targets and the command post. The performace of the developed system is verified via outdoor experiments.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.9
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• pp.156-163
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• 2013

In this paper, we propose an algorithm for estimating media characteristics of sea water and subbottom multi-layers. The proposed algorithm for estimating reflection coefficients, uses a transmitted signal and reflected signal obtained from multiple layers of various shape and structure, and the algorithm is called Schur algorithm. The algorithm is efficient in estimating the reflection coefficients since it finds solution by converting the given inverse scattering problem into matrix factorization. To verify the proposed algorithm, we generate a transmit signal and reflected signal obtained from lattice filter model for sea water and subbottom of multi-level non-homogeneous layers, and then find that the proposed algorithm can estimate reflection coefficients efficiently.

• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.7
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• pp.723-728
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• 2016

This study is analyzed the optical property of red tide pixel by using Landsat-7 ETM+, Landsat-8 OLI and COMS/GOCI image. In order to sample red tide pixel, Landsat-7, 8 true color image were used and obtained coordinate of red tide pixel in the true color image. Normalized water leaving radiance(nLw) and absorption coefficient were obtained from GOCI image in the same coordinate of the true color image. When red tide was not occurred the main absorption range was 412nm and 660nm but when red tide occurred it was 660nm and absorption coefficient in 412nm are drastically reduced. It made no difference of nLw spectrum between red tide pixel and non red tide pixel in nLw, but the absolute value of nLw was low than non red tide pixel, especially 660nm and 680nm wavelength sharply decrease.

• Journal of Satellite, Information and Communications
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• v.8 no.1
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• pp.14-22
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• 2013

GPS radio occultation is a remote sensing technique probing atmospheric properties based on the fact that GPS signal is refracted and delayed by atmosphere. The FORMOSAT-3/COSMIC mission jointly developed by the USA and Taiwan is providing about 2500 occultation soundings a day on the near real-time basis. The Korean KOMPSAT-5/AOPOD system is preparing to launch for monitoring troposphere and ionosphere using a dual frequency GPS receiver and the antenna for occultation data acquisition. In this paper, we examine the methods for signal processing and the geometry analysis for GPS radio occultation, and look into the retrieval techniques for the temperature and humidity of troposphere and the electron density and scintillation of ionosphere. Using these atmospheric properties, we aim to derive the strategies for applying GPS radio occultation to space weather, for example, ionospheric TEC(total electron content) analysis for earthquake monitoring and the Open API(application programming interface) development for more effective data service.

• Tunnel and Underground Space
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• v.17 no.1 s.66
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• pp.66-74
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• 2007

The analysis of ground subsidence stability was conducted for the residential area located on the limestone corrosion zone. For the investigation of the cavity distribution in limestone region, various geophysical investigations such as electroresistivity tomography, electromagnetic prospecting are carried out. Geotechnical field tests with drilling are also carried out for the evaluation of the ground characteristics. Based upon their results, numerical modeling is performed for the simulation and prediction of the ground subsidence with the conditions of cavity geometry and groundwater level. The main factor to cause the ground subsidence is estimated as the draw down of the groundwater level below soil overburden, which disturbs the mechanical equilibrium of ground and drives washing away the overburden soil through the cavity and solace subsidence. It seemed that it is essential to maintain the groundwater level continuously above the shallow cavity for the prevention of the ground subsidence on the limestone corrosion zone.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.130.1-130.1
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• 2011

인류의 우주공간에 대한 영향력이 확대됨에 따라, 우주공간에서의 인위적인 활동에 영향을 미칠 수 있는 모든 종류의 상황들에 대한 이해가 최근 전 세계적으로 매우 중요한 이슈로 부상하고 있다. 이를 Space Situational Awareness (SSA)라고 하는데, 특히 근지구공간에서의 인위적, 자연적 우주물체는, 우주발사체의 지속적인 증가와 이리듐-코스모스 위성의 상호 충돌 및 중국 폐기위성 파괴 등과 같은 사건으로 기하급수적으로 증가된 우주물체의 개체수로 인해 대한민국 국적의 모든 위성에도 실제적인 위협 요인으로 대두되고 있다. 이에 기초 기술연구회와 한국천문연구원은 이러한 위협을 국가적으로 해결해야할 과제(National Agenda Project) 중의 하나로 정의하고, 이를 해결하기 위해 우주물체 전자광학 감시체계 기술개발(OWL; Optical Wide-field patroL) 사업을 시작하였다. 이 사업의 목표는 자국위성에 대한 궤도력을 독자적으로 유지할 수 있는 시스템을 개발하는 것이며, 이를 위하여 2011년부터 6년 동안 총 5개소의 해외 관측소에 50cm급 광시야 망원경을 각각 설치하여 자국위성을 자동으로 상시관측하고, 관측된 자료를 이용한 궤도계산을 통하여 독자적으로 궤도력을 유지할 계획이다. 또한, 우주잔해물 감시는 하나의 국가에서 단독으로 할 수 없기 때문에 2m급 우주물체 감시망원경을 개발하여 국제공동으로 진행할 계획이다. 사업 첫해인 2011년 4월 시스템 요구사항 분석을 완료하였고 10월말 시스템 기본설계를 완료할 예정이다. 최종 완성될 소구경 광시야 망원경과 우주물체 감시망원경의 주요 임무는 우주물체 관측이지만, 향후 광시야를 이용한 다양한 탐사천문학에도 기여할 수 있을 것으로 기대한다. 한편, 자국위성에 대한 충돌 위험도 분석 및 회피기동에 관한 연구는 한국항공우주연구원이 이 사업의 협동연구로 참여하고 있다.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.3
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• pp.47-54
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• 2001

This study is to analyze the impedance response in human body by acoustic stimulation on acupoints and contrast parte; for objectification of the meridian substance. It is to verify meridian pathway and channel theory or bio-energy in body. This paper proposes to make an hypothesis about the underground water theory. The meridian has not tube or pipe line type channel but bio-energy flow along the channel similar to flowing pattern of underground water in body. It was analyzed the current characteristic or impedance response after acoustic stimulation by sound wave of 5 specific tones. The response characteristics of current stimulation are measured by the average current magnitude and variation ratio or meridian. The current variation ratio or Live Meridian(gung) 33.2%, Heart Meridian(sang) 30.7% Kidney Meridian (gak) 33.1%, Spleen Meridian(chi) 33.9%, Lung Meridian (wo) 30.7% are to be compared to contrast parts (non-acupoint and meridian). In experimental results, meridian is discrimination to non-meridian, and 5 vital meridians have a reciprocal relationship with sound wave of 5 specific tones.