• Geophysics and Geophysical Exploration
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• v.6 no.2
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• pp.71-76
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• 2003

Accurate estimation of the first arrival travel time is an essential task to obtain a high resolution velocity tomogram. Accuracy of the travel time estimation may be influenced by two factors; geological and mechanical. A serious mechanical factor is the source firing control problems. We found the control problems in the records generated by tome impulsive borehole sources. The problems are; irregular firing control and uncertainty in estimation of the absolute firing-times shown in records. Definitely, the time difference will introduce an error to the first arrival times, and accordingly; it will cause some distortion in the resulting velocity tomogram. A method to determine the firing time is suggested here. The method determines the optimum onset time by comparing the horizontal and the NMO velocity with various amount of delay time adjustment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.10
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• pp.907-911
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• 2007

This paper dealt with the frequency spectrum analysis of acoustic signal produced by partial discharge (PD) in insulation oil and the positioning of PD occurrence to apply in diagnosis of oil insulated transformers. Three types of electrode system ; the needle-plane, the plane-plane, and the wire-wire structure were assembled to simulate partial discharges in oil insulated transformers. A low-noise amplifier and a decoupling circuit were designed to detect acoustic signal with high sensitivity The frequency spectrum of the acoustic signal were 50 kHz ${\sim}$ 260 kHz in the needle-plane, 50 kHz ${\sim}$ 250 kHz in the plane-plane, and 45 kHz${\sim}$195 kHz in the wire-wire electrode system. Their peak frequencies were 145 kHz, 130 kHz and 114 kHz, respectively The position of PD occurrence was calculated by the time difference of arrival (TOA) using three acoustic emission (AE) sensors, and we could find the position within the error of 1 % in the experimental apparatus.

• The Korean Journal of Emergency Medical Services
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• v.22 no.3
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• pp.47-54
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• 2018

Purpose: The purpose of this study was to present evidence for quality management based on analysis of patient transportation and response intervals among emergency medical squads. Methods: The chi-square test was used to determine whether mental status and patient assessment affected direct medical control and hospital destination. One way analysis of variance was used to compare response intervals depending on mental status and patient assessment using data drawn from 1172 prehospital care reports. Results: There was a statistically significant relationship between mental status and direct medical control (p<.001); there was a statistically significant relationship between patient assessment and hospital destination (p=.011). However, there was no statistically significant relationship between mental status and hospital destination. The interval from arrival at the patient's side to departure from the scene showed a statistically significant difference (p<.001, p<.001), however, it took the longest time (16.8 minutes) in unresponsive patients. It showed a statistically significant difference (p<.001) in the interval from arrival at patient's side to departure from the scene depending on patient assessment; however, it took the longest time (9.6 minutes) in emergency patients. Conclusion: There was call for direct medical control based on patient assessment; however, patient transportation and response intervals were not appropriate.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.7
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• pp.76-84
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• 2013

In the passive emitter localization using instantaneous TDOA (time difference of arrival) and FDOA (frequency difference of arrival) measurements, the estimation accuracy can be improved by collecting additional measurements. To achieve this goal, it is required to increase the number of the sensors. However, in electronic warfare environment, a large number of sensors cause the loss of military strength due to high probability of intercept. Also, the additional processes should be considered such as the data link and the clock synchronization between the sensors. Hence, in this paper, the passive localization of a stationary emitter is presented by using the successive TDOA and FDOA measurements from two moving sensors. In this case, since an independent pair of sensors is added in the data set at every instant of measurement, each pair of sensors does not share the common reference sensor. Therefore, the QCLS (quadratic correction least squares) methods cannot be applied, in which all pairs of sensor should include the common reference sensor. For this reason, a Gauss-Newton algorithm is adopted to solve the non-linear least square problem. In addition, to show the performance of the proposed method, we compare the RMSE (root mean square error) of the estimates with CRLB (Cramer-Rao lower bound) and derived the CEP (circular error probable) planes to analyze the expected estimation performance on the 2-dimensional space.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.12
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• pp.1100-1107
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• 2015

In this paper, we propose an algorithm to identify Wobble PRI and Sinusoidal PRI among Radar pulses. We applied not only the DTOA(Difference Time Of Arrival) concept of radar pulse signals incoming to antennas but also a rising and falling cub characteristic of those PRIs. After making a program by such algorithm, we input each 40 data to Wobble PRI's and Sinusoidal PRI's identification programs and in result, those programs fully processed the data the according to expectations. In the future, those programs can be applied to the ESM, ELINT system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.8
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• pp.1392-1399
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• 2016

Blackout effect occurs when a driver misadapts to the changed lighting conditions upon entering a tunnel. This could lead to a decrease in visibility especially in the daylight, depending on the difference in the degree of brightness between inside and outside the tunnel. To alleviate such a problem, we decrease windshield transparency before the driver arrives at the tunnel entrance. Controlled amount of light inside the car can allow the drivers to adjust to the dark prior to entering. The windshield transparency coefficient is to be determined by the arrival time at the tunnel and difference in the level of brightness between inside and outside the tunnel. Navigation, road sign detection, and tunnel entrance detection provide the arrival time. We also designed an opto-electronic conversion function to estimate the level of brightness. The black-hole phenomenon alleviation method is verified by field experiments using an automobile camera and a navigation. The result shows that the adjusted windshield transparency is able to provide an environment with a comfortable level of brightness with which the drivers can enter tunnels without the visibility problem.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.2
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• pp.121-127
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• 2011

As considerable interests in noise emission from a ship have been increased, the need for localization of noise sources of the marine propeller generating cavitation and singing noise is looming large. In many practical cases, cavitation and singing noise occur on a particular position of the certain blade of the propeller. It is so important to know the position of noise source correctly in order to eliminate or suppress unwanted noise. In this study, we develop "noise source localization technology" using TDOA method. Experimental measurements carried out at the circulating water channel and towing tank show that noise source can be clearly identified and localized using TDOA method.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.147-148
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• 2008

In this paper two kinds of techniques were compared for localization of PD(partial discharge) in power transformer and more useful method was suggested. Both of them, the time of arrival and the energy content method, were tested in 154kV single phase experimental transformer using UHF signal measurement. The former was using the difference of arrival time of recorded signals from four UHF sensors, the latter was based on the energy content in frequency spectra of signals detected at all sensors.

• Journal of Advanced Navigation Technology
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• v.15 no.2
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• pp.234-240
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• 2011

In this paper, the performances of Cram$\acute{e}$r-Rao Lower Bound (CRLB) with Frequency Difference of Arrival (FDOA) measurements for Unmanned Aerial Vehicle (UAV) tracking are investigated. We focus on two cases: the influence on CRLB with FDOA measurements collected by time, and random distribution of Ground Stations (GSs). We derived the performance by gauging the size of CRLB through Complementary Cumulative Distribution Function (CCDF). From the simulation results, broader distribution of GSs and FDOA measurements by longer time bring about better performance.

• Journal of Satellite, Information and Communications
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• v.4 no.1
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• pp.21-27
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• 2009

In this paper, we introduce a simulation result of cross ambiguity function (CAF) using time difference of arrival and frequency difference of arrival. This method is generally used to find a geographical location of the unknown radio transmitter. If multiple signals with the same source information are arrived at a receiver via different paths, then they will have different time delays and Doppler shifts. We can estimate the CAF by using these characteristics, and estimate the location of the unknown transmitter. This paper introduces a technique to improve the estimation performance of CAF.