• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.6
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• pp.1056-1063
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• 2015

Waves can be expressed in terms of a spectrum; that is, the energy density distribution of a representative wave can be determined using statistical analysis. The JONSWAP, PM and BM spectra have been widely used for the specific target wave data set during storms. In this case, the extracted wave data are usually discontinuous and independent and cover a very short period of the total data-recording period. Previous studies on the continuous wave spectrum have focused on wave deformation in shallow water conditions and cannot be generalized for deep water conditions. In this study, the Generalized Extreme Value (GEV) function is proposed as a more-optimal function for the fitting of the continuous wave spectral shape based on long-term monitored point wave data in deep waters. The GEV function was found to be able to accurately reproduce the wave spectral shape, except for discontinuous waves of greater than 4 m in height.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.709-712
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• 1988

Ultrasonic Doppler Diagnostic System utilizes the Doppler effect for measurement of blood velocity. The sign of the Doppler frequency shift represents blood flow direction. CW(Continuous-Wave) Doppler System uses quadrature detection and phase rotation method to produce simultaneous independent audio and velocity signals for forward and reverse blood flow direction in the time-domain, had been fabricated. But time-domain analyzing such as audio evaluation and zero- crossing detection for instantaneous and mean frequnecy measurement do not provide both an accurate and quantitative result. Therefore, it is necessary to adopt frequency-domain technique to improve system performance. In this paper, we describe a unit which is composed of CW Doppler System and real-time spectrum analyzer (installed TMS 32010 DSP Chip). This unit shows time-dependent spectrum variation and mean velocity of Blood signal.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.9
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• pp.757-763
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• 2013

This study discusses the multiple knife-edge diffraction loss with the receiver and jammer located in the Seoul metropolitan northwestern region. The considered positioning and jamming signals are the GPS L1 C/A signal and several jamming signals such as the wideband Gaussian noise, matched spectrum, and continuous wave signals. To calculate the accurate diffraction effects, the 3-dimensional topography data at the Seoul metropolitan northwestern region was used.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.240-244
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• 1998

Cavity ring-down spectroscopy (CRDS) is a high-sensitive laser spectroscopic technique capable of measuring concentrations of trace gases. We have demonstrated a new design of the CRDS spectrometer with a continuous wave (CW) laser. The ring-dwon signal is produced through blocking the incident CW laser by scanning the cavity length fast toward off-resonance iwth PZT (piezoelectric transducer). We have also measured an absorption spectrum of acetylene overtone transitions near 570 nm at the pressure of 2700 Pa, and the minimum detectable absorption coefficient has been found to be about $3{\times}10^{-9}\cm^{-1}$.

• Current Optics and Photonics
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• v.3 no.5
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• pp.466-472
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• 2019

A system for continuous-wave coherent Doppler lidar (CW lidar), made up of all-fiber structures and a coaxial transmission telescope, was set up for wind measurement in Hefei (31.84 N, 117.27 E), Anhui province of China. The lidar uses a fiber laser as a light source at a wavelength of $1.55{\mu}m$, and focuses the laser beam on a location 80 m away from the telescope. Using the CW lidar, radial wind measurement was carried out. Subsequently, the spectra of the atmospheric backscattered signal were analyzed. We tested the noise and obtained the lower limit of wind velocity as 0.721 m/s, through the Rayleigh criterion. According to the number of Doppler peaks in the radial wind spectrum, a classification retrieval algorithm (CRA) combining a Gaussian fitting algorithm and a spectral centroid algorithm is designed to estimate wind velocity. Compared to calibrated pulsed coherent wind lidar, the correlation coefficient for the wind velocity is 0.979, with a standard deviation of 0.103 m/s. The results show that CW lidar offers satisfactory performance and the potential for application in wind measurement.

• Journal of the Optical Society of Korea
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• v.14 no.1
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• pp.49-54
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• 2010

In this study, the use of a continuous-wave (CW) supercontinuum (SC) seeded by an erbium-doped fiber's amplified spontaneous emission (ASE) for optical-coherence tomography imaging is experimentally demonstrated. It was shown, by taking an in-depth image of a human tooth sample, that due to the smooth, flat spectrum and long-term stability of the proposed CW SC, it can be readily applied to the spectral-domain optical-coherence tomography system. The relative-intensity noise level and spectral bandwidth of the CW SC are also experimentally analyzed as a function of the ASE beam power.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.118-122
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• 2000

In this study, Ringing is investigated by continuous wavelet transform. Ringing is considered to be one of the typical transient phenomena in the field of ocean engineering. The wavelet analysis is adopted to analyze ringing from the point that wavelet analysis is capable of frequency analysis as well as time domain analysis. The use mother wavelet is the Morlet wavelet. The relation between the frequency of the time series and that of wavelet can be clearly defined with Mor1et wavelet. Experimental data obtained by other researchers was used. The wave height time series and acceleration times series of the surface piercing cylinder were analyzed. The results show that the proposed scheme can detect typical frequency region by the time domain analysis which could hardly be detected if one relied on the frequency analysis.

• The Journal of the Acoustical Society of Korea
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• v.23 no.7
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• pp.514-520
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• 2004

There are many techniques for underwater source localization. These are the methods based on TDOA (Time Difference Of Arrival) estimation. beamforming techniques and high resolution techniques, etc. In this Paper we estimate the underwater source position using MCPSP (Modified Cross Power Spectrum Phase) function that is calculated on frequency domain using sensors of small number. However, the performances of the localizing method based on MCPSP function drops greatly in the case of CW (Continuous Wave) signal . In this Paper we proposed the TDOA estimation method for pulsed CW signal. In the Proposed method we composed of new segment including a edge of ping. This segment was computed by short-time energy detection. With theoretical representation the performances of the proposed method were analyzed under various environment.

• Proceedings of the Optical Society of Korea Conference
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• 2009.10a
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• pp.233-234
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• 2009

In this paper, we report the characteristics of the continuous wave laser output of the $lima{\varsigma}on$-shaped InGaAsP microcavity laser pumped by current injection. In order to find the directions of emission far-field patterns are measureed by rotating an optical fiber around the microcavity. We observe high directionality of the $lima{\varsigma}on$-shaped microcavity laser. For the analysis of lasing properties we also investigate its polarization and spectrum using the Glan-Thompson polarizer and spectrum analyzer.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.668-670
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• 2010

It is necessary to estimate the range and Doppler shifted spectrum for the extraction of useful information from the return echoes in the frequency modulated continuous wave radar systems used for the remote sending purpose such as detection of moving targets. However, the spectrum estimation using the FFT method causes the very large sidolobes of clutter masking the essential signal information if the acquisition time of an echo signal is pretty short. Therefore, in this paper, the efficient data windowing method is investigated to suppress the strong sidelobe levels of the clutter and results are analyzed.