• Korean Journal of Remote Sensing
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• v.15 no.1
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• pp.61-71
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• 1999

Several physical phenomena on the sea surface are analyzed from SAR images of South Sea areas, Korea. Strong wave patterns propagating in southerly direction are seen in ERS-1 SAR image on October 11, 1994, and a wave directional spectrum is calculated from this image using the SAR modulation transfer function. RADARSAT SAR image of August 15, 1996 reveals internal waves in northern coastal waters of Cheju Island. Analysis indicates that the internal waves may have been generated by the tidal currents traveling over the shallow bottom of the stratified water in the summer during the tidal changeovers fro ebb to flood and shows patterns of trains of solitons. RADARSAT SAR image taken 3 days after the oil spill accident near Goeje Isalnd on April 3, 1997 detects distinct oil slicks from the accident area but also shows slicks near the coast caused by wind sheltering of coastal mountains and chemical-biological activities.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.5
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• pp.1069-1076
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• 2017

C-ITS(Cooperative-Intelligent Transportation System) provides services that require strict real-time such as forward collision warning, road safety service and emergency stop. WAVE(Wireless Access in Vehicular Environments), a core technology of C-ITS, is a technology designed for high-speed driving. However, in order to provide stable communication service by applying to real road environment, various performance tests of real vehicular environment are required. In the real road environment, WAVE communication performance is influenced by the surrounding environment such as moving vehicle, road shape and topography. Especially, when the vehicle is moving at high speed, the traveling position according to the speed of the vehicle, The surrounding environment changes rapidly. Such changes are factors affecting the communication performance, therefore a system and methods for analyzing them are needed. In this paper, we propose the configuration and test method of an effective performance evaluation system under high-speed driving and describe the results of analyzing the communication performance based on the data measured through the actual vehicle test.

• Journal of the Korean Geotechnical Society
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• v.23 no.7
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• pp.5-16
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• 2007

The monitoring and investigation of underwater landslide help to understand its mechanism, increase the usefuless of design and construction and reduce the losses. This paper presents three high resolution geophysical techniques electrical resisitance, ultrasonic wave reflection imaging, and shear wave tomography conducted to determine the lab-scaled submerged landslide. Electrical resistance profiles of a soil mass obtained by an electrical resistance probe provide detailed information to assess the spatial distribution of the soil mass with milimetric resolution. An ultrasonic wave image obtained by recording the reflections from interfaces of different impedance materials permits detecting layers and landslide with submilimetric resolution. The pixel based image of immersed landslides is created by the inversion of the boundary information achieved from the traveling time of shear waves. The experimental results show that the ultrasonic wave imaging and the electrical resistance can provide complementary information; and their association with S-wave tomography image can produce a 3-D view of the underwater landslide. This study suggests that geophysical techniques may be effective tools for the detection of the underwater landslides and spatial distribution offshore.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.98-98
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• 2014

Due to the simple vertical structure of magnetic field, pores can be exploited to study the transport of mechanical energy by waves along the magnetic field to the chromosphere and corona. For a better understanding of physics of pores, we have investigated chromospheric traveling features running across two merged pores from their centers at the speed about 55 km s-1, in the active region AR 11828. The pores were observed on 2013 August 24 by using high time, spatial, and spectral resolution data from the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New Solar Telescope (NST). We infer a LOS velocity by applying the bisector method to the Ca II $8542{\AA}$ band and $H{\alpha}$ band, and investigate intensity and the line-of-sight velocity changes at different wavelengths and different positions at the pores. We find that they have 3 minutes oscillations, and the intensity oscillation from the line center is preceded by that from the core ($-0.3{\AA}$) of the bands. There is no phase difference between the intensity and the LOS velocity oscillations at a given wavelength. The amplitude of LOS velocity from near the core spectra is greater than that from the far core spectra. These results support the interpretation of the observed wave as a slow magnetoacoustic wave propagating along the magnetic field lines in the pores. The apparent horizontal motion and a sudden decrease of its speed beyond the pores can be explained by the projection effect caused by inclination of the magnetic field with a canopy.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.1
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• pp.38-47
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• 2007

The initiation of fatigue cracks in a simulated aircraft structure with a series of rivet holes was detected by acoustic emission(AE), then the crack length was determined by surface acoustic wave(SAW) technique. With the initiation and growth of fatigue cracks, AE events increased intermittently to form a stepwise incremental curve of cumulative AE events whereas the crack length increased more or less monotonically. With the SAW technique employed, the crack sizing for 13 different cracks including some short cracks was performed. With the reference to the measurement by traveling microscope, cracks in the range of $1{\sim}8mm$ long were reliably sized by the SAW technique. Although it was impossible to size the short fatigue cracks in the range shorter than 1 mm, the SAW technique still appeared practically useful for a range of crack lengths often found in aircraft structures.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.1
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• pp.133-138
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• 2008

To analyze incident waves traveling from the deep ocean is very important in that it is based on resolving problems occurred in coastal areas. In general, numerical models and analytical solutions are used to analyze wave transformation. Although a numerical model can be applied to various bottoms and wave conditions, it may have some cumbersome numerical errors. On the other hand, an analytical solution has an advantage of obtaining the solution quickly and accurately without numerical errors. The analytical solution can, however, be utilized only for specific conditions. In this study, the analytical solution of the mild-slope equation has been developed. It can be applied to various conditions combing a numerical technique and an analytical approach while minimizing the numerical errors. As a result of comparing the obtained solutions in this study with those of the previously developed numerical model, A good agreement was observed.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.5 no.3
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• pp.101-109
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• 2012

Because the installation problem of parabola antenna that is tilted to 45 degree when this antenna is installed at the area of middle latitude, the study on planar antenna in place of parabola antenna is made rapid progess. Especially, The development of the planar antenna for VSAT is needed depending on the increased Ka-band satellite communications. In this paper, in order to meet with these performances, an array antenna consisting of the vertical polarized waveguide longitudinal slots based on the leaky-wave mode of traveling wave antenna is proposed. Especially, for the lower sidelobe level, the design method of the radiation power distribution control using the different slot widths is proposed. An array antenna consisting of 32 leakywave waveguide antennas is showing 35.16 dBi of gain, 2.5 degree of beamwidth at azimuth, below than -30 dB of sidelobe level, 45.8 degree of beam tilt angle in center frequency 30.2 GHz.

• Current Optics and Photonics
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• v.2 no.5
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• pp.474-481
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• 2018

We propose a polarization phase-shifting technique to investigate the thickness of $Ta_2O_5$ thin films deposited on BK7 substrates, using a modified Sagnac interferometer. Incident light is split by a polarizing beam splitter into two orthogonal linearly polarized beams traveling in opposite directions, and a quarter-wave plate is inserted into the common path to create an unbalanced phase condition. The linearly polarized light beams are transformed into two circularly polarized beams by transmission through a quarter-wave plate placed at the output of the interferometer. The proposed setup, therefore, yields rotating polarized light that can be used to extract a relative phase via the self-reference system. A thin-film sample inserted into the cyclic path modifies the output signal, in terms of the phase retardation. This technique utilizes three phase-shifted intensities to evaluate the phase retardation via simple signal processing, without manual adjustment of the output polarizer, which subsequently allows the thin film's thickness to be determined. Experimental results show that the thicknesses obtained from the proposed setup are in good agreement with those acquired by a field-emission scanning electron microscope and a spectroscopic ellipsometer. Thus, the proposed interferometric arrangement can be utilized reliably for non-contact thickness measurements of transparent thin films and characterization of optical devices.

• ETRI Journal
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• v.26 no.6
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• pp.589-596
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• 2004

Packaging technologies for a broadband and narrowband modulator with a traveling wave electro-absorption modulator (TWEAM) device were developed. In developing a broadband modulator, the effects of the device and packaging designs on the broadband performance were investigated. The optimized designs were obtained through a simulation with the result that we developed a broadband modulator with a 3 dB bandwidth of 38 GHz in the electrical-to-optical (E/O) response, an electrical return loss of less than -10 dB at up to 26 GHz, an rms jitter of 1.832 ps, and an extinction ratio of 5.38 dB in a 40 Gbps non-return to zero (NRZ) eye diagram. For analog application, the effect of the RF termination scheme on the fractional bandwidth was studied. The microstrip line with a double stub as a matching circuit and a laser trimming process were used to obtain an $S_{11}$ of -34.58 dB at 40 GHz and 2.9 GHz bandwidth of less than -15 dB.

• Journal of Magnetics
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• v.21 no.3
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• pp.450-459
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• 2016

Experimental results and data of numerical simulations are presented, concerning generation of wideband radio frequency (RF) oscillations in a nonlinear transmission line (NLTL) which contains a pre-magnetized core of ferrite material. Emphasis is made on the means for extracting the RF signal from the line, in order to radiate it into free space. Antennas of two types that can be used for the purpose are considered, both featuring a coaxial design. This permits availing of the principal advantages of coaxial systems, such as operation in the mode of a traveling TEM wave; wide range of the transmitted frequencies, and a reasonably simple design. The antennas studied, specifically a disc-cone dipole (DCD) and an impulse reflector antenna ('Half-IRA', or HIRA type) differ significantly in effective width of the radiated spectrum and in spatial characteristics of the radiated field in far region.