• 지구물리와물리탐사
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• 제13권1호
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• pp.51-60
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• 2010

남극 킹조지섬 포케이드 빙하의 저면 지형과 내부 모습을 규명하기 위해서 2006년 11월에 4개 조사측선을 따라 헬리콥터 및 지상 레이다(GPR) 탐사를 실시하였다. 혼합위상인 단채널 지상 GPR 자료에 적용한 신호 역대합, f-k 구조보정 속도분석, 유한차분 깊이구조보정 등의 처리과정을 통하여 수직 분해능 향상, 속도함수 추출, 선명한 깊이영상 작성 등을 효과적으로 수행하였다. 헬리콥터 GPR 자료의 경우, 구조보정속도는 공기와 얼음의 2층모델을 가정한 평균제곱근속도로 구하였다. GPR 단연은 울퉁불퉁한 빙저면, 빙하 내부의 미끄러짐면, 운집된 산란잡음 등의 특징적 모습을 보여준다. 기반암까지의 최대 깊이는 포케이드 빙하와 목지들로우스키 빙하 사이의 경계능선 남동사면에 인접한 빙하 골짜기에서 79 m가 넘는다. 빙하 기저수 위에 복잡한 형태의 굴과 수 m의 폭을 갖는 독립된 빈 공간들의 존재를 지상 GPR 자료로부터 해석하였다. 빙하 중단 부근의 GPR 영상은 포토소만의 빙산 형성기작과 관련된 미끄러짐면, 단열, 단층 등의 구조를 보여준다.

• Current Optics and Photonics
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• 제7권5호
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• pp.545-556
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• 2023

This paper introduces volume-sharing multi-aperture imaging (VMAI), a potential approach proposed for volume reduction in space-borne imagers, with the aim of achieving high-resolution ground spatial imagery using deep learning methods, with reduced volume compared to conventional approaches. As an intermediate step in the VMAI payload development, we present a phase-1 design targeting a 1-meter ground sampling distance (GSD) at 500 km altitude. Although its optical imaging capability does not surpass conventional approaches, it remains attractive for specific applications on small satellite platforms, particularly surveillance missions. The design integrates one wide-field and three narrow-field cameras with volume sharing and no optical interference. Capturing independent images from the four cameras, the payload emulates a large circular aperture to address diffraction and synthesizes high-resolution images using deep learning. Computational simulations validated the VMAI approach, while addressing challenges like lower signal-to-noise (SNR) values resulting from aperture segmentation. Future work will focus on further reducing the volume and refining SNR management.

• 항공우주기술
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• 제12권2호
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• pp.30-39
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• 2013

본 논문에서는 정지궤도복합위성 기상탑재체의 보정 과정 및 영상 복사성능 품질 측정 방법에 대한 사항들을 기술하였다. MTF(Modulation Transfer Function), SNR(Signal-To-Noise Ratio), NEdT(Noise Equivalent Delta Temperature) 및 Dynamic Range 등 위성용 가시광선 및 적외선 센서의 복사성능과 관련된 품질 측정을 위한 주요 파라미터들에 초점을 맞추었다. 지상시험과정에서 측정한 이들 파라미터들의 기준 값들을 발사 후 궤도상 시험기간에 측정한 값들을 비교 검토하는 작업이 영상품질 측정의 핵심적인 과정이다. 천리안위성의 궤도상 시험기간 동안 이루어진 기상탑재체의 영상 품질 분석 과정의 사례들을 바탕으로 마련된 정지궤도 복합위성의 기상탑재체 영상의 복사성능 검정 방법에 대한 논의도 기술하였다.

• 한국전자파학회논문지
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• 제15권3호
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• pp.311-318
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• 2004

PCM/FM과 같은 디지털 변조 방식의 텔레메트리 시스템에 있어서 비트 에러율(BER)을 최소화하여 수신된 신호의 품질을 향상시키기 위해서는 충분히 안정된 신호마진을 갖도록 회선설계가 이루어져야 한다. 특히 고속으로 이동하는 비행체의 경우에는 비행체 자세에 따른 송수신 안테나 사이의 안테나 이득패턴의 변화와 비행거리에 따른 손실이 동반되어지며 이로 인해서 회선상의 요동이 발생된다. 본 논문에서는 2002년 11월에 한국항공 우주연구원에서 시험 발사되었던 국내 최초 액체로켓 KSR-III의 비행시험 중에 S-대역 지상국에서 측정된 텔레메트리 신호의 신호대잡음비(SNR) 변화와 로켓의 비행 궤적 및 롤, 피치, 요 등의 자세변화를 고려하여 시뮬레이션으로 계산된 결과를 비교 분석하였으며 이를 통해 회선마진의 변화가 잘 일치함을 확인할 수 있었다. 또한, 탑재 안테나 개수가 1개인 경우와 롤 변화가 없는 가상의 비행 상황에 대해서 시뮬레이션을 수행하여 회선 변화를 예측할 수 있었다.

• Structural Monitoring and Maintenance
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• 제1권1호
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• pp.131-157
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• 2014

Special track systems used to divert a train to other directions or other tracks are generally called 'railway turnout'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, 'fibre-reinforced foamed urethane (FFU)' bearers, has been carried out at a complex turnout junction under heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle 'AK Car'), track settlement (based on survey data), track dynamics, and acoustic characteristics have been measured. Operational train pass-by measurements have been analysed to evaluate the effectiveness of the replacement methodology. Comparative studies show that the use of FFU bearers generates higher rail and sleeper accelerations but the damping capacity of the FFU help suppress vibration transferring onto other track components. The survey data analysis suggests a small vertical settlement and negligible lateral movement of the turnout system. The static and dynamic behaviours of FFU bearers appear to equate that of natural timber but its service life is superior.

• Smart Structures and Systems
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• 제19권1호
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• pp.1-10
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• 2017

The operation of subway trains induces secondary structure-borne vibrations in the nearby underground spaces. The vibration, along with the associated noise, can cause annoyance and adverse physical, physiological, and psychological effects on humans in dense urban environments. Traditional tethered instruments restrict the rapid measurement and assessment on such vibration effect. This paper presents a novel approach for Wireless Smart Sensor (WSS)-based autonomous evaluation system for the subway train-induced vibrations. The system was implemented on a MEMSIC's Imote2 platform, using a SHM-H high-sensitivity accelerometer board stacked on top. A new embedded application VibrationLevelCalculation, which determines the International Organization for Standardization defined weighted acceleration level, was added into the Illinois Structural Health Monitoring Project Service Toolsuite. The system was verified in a large underground space, where a nearby subway station is a good source of ground excitation caused by the running subway trains. Using an on-board processor, each sensor calculated the distribution of vibration levels within the testing zone, and sent the distribution of vibration level by radio to display it on the central server. Also, the raw time-histories and frequency spectrum were retrieved from the WSS leaf nodes. Subsequently, spectral vibration levels in the one-third octave band, characterizing the vibrating influence of different frequency components on human bodies, was also calculated from each sensor node. Experimental validation demonstrates that the proposed system is efficient for autonomously evaluating the subway train-induced ambient vibration of underground spaces, and the system holds the potential of greatly reducing the laboring of dynamic field testing.