• Journal of the Korean earth science society
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• v.30 no.7
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• pp.824-833
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• 2009

We analyzed a total of six months of geomagnetic data obtained at Cheonyang observatory, which is operated by Korean Meteorological Administration, to monitor earthquake precursors. Geomagnetic transfer functions (GTFs) and polarization values, which reflect the time-variations of the resistivity of subsurface, were estimated from 3-component geomagnetic data. The time-variant fluctuations were compared with the earthquake events occurred in the same period. Now that the daily GTFs show fairly irregular variations, we can not identify any correlation with the already occurred earthquakes and Kp index. On the other hand, we detect clear increases of the Ultra-Low-Frequency (ULF) band polarization values before the earthquakes, but the similar features are also observed even though the earthquake did not occur. This result may indicate that these time-variations are not just due to the earthquake precursor. For further understanding about these results, we need to investigate the relationship between the previous earthquake events and the geomagnetic data of other observatories.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.7
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• pp.552-558
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• 2014

In this paper, we propose a side-peak cancellation technique of composite binary offset carrier (CBOC) signals for e-navigation. First, we divide a CBOC sub-carrier into several sub-carrier pulses, and then, observe that CBOC autocorrelation is the sum of multiple sub-correlation functions. Finally, we propose a novel correlation function with no side-peak and a sharp main-peak by combining the sub-correlation functions to improve the positioning accuracy. From numerical results, we confirm that the proposed correlation function with a sharp main-peak provides a better positioning performance than the conventional correlation functions in terms of the tracking error standard deviation.

• Proceedings of the KSEEG Conference
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• 2001.04a
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• pp.407-409
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• 2001

• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.4
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• pp.80-88
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• 2003

Radar signal simulation is increasingly gaining in importance according as modem radar systems are more complex. Although computer performance has been advanced, it is difficult to implement the real-time simulation because the detailed model for the radar is necessary to get the desired accuracy. In order to achieve real time operation, we propose radar signal generation technique using ambiguity function, Instead of wellknown correlation method. The ambiguity function is the mathematical modeling of the signal processing procedure which is a simulation section to require the most computations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5A
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• pp.367-374
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• 2012

In this paper, we propose a novel cancellation scheme of correlation side-peaks for binary offset carrier (BOC) signals. The proposed scheme is based on a combination of the sub-correlation functions composing the BOC autocorrelation and applicable to both sine- and cosine-phased BOC signals without requiring any auxiliary signal in the receiver. From numerical results, it is confirmed that the proposed scheme provides a better tracking accuracy than the conventional schemes.

• Economic and Environmental Geology
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• v.38 no.2 s.171
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• pp.155-163
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• 2005

For an unbiased TF (Tansfer Function) estimations we investigate geomagnetic TF derived from ICHEON and YONGIN sites, employing RR (Remote Reference) and SNS (Signal Noise Separation) techniques. The Rh technique, which requires synchronized field variations recorded at a clean remote site, is a reliable method to minimize the bias of TF by uncorrelated noises in magnetic channels. Meanwhile, SNS technique based on the assumption of noise-free remote data can improve the signal-noise level by separating signal TF and noise TF, which is successfully applied to the environments with strong correlated noises. In this study, TF at YONGIN is analyzed using geomagnetic data from ICHEON site as a remote reference, which seem to have somewhat better data quality. The application of Rh technique reduces the bias of TF, which appears in single site robust estimation, and makes curves in the amplitude and phase of TF more smooth as frequency. Futhermore, in order to investigate noise source quantitatively, SNS technique is applied. The results of SNS suggest that dominant noise source seems to be located at western region of YONGIN. This noise source is considered to originate from railway system such as KTX and national subway. which passes through the west regions of YONGIN.

• Journal of the Korean Data and Information Science Society
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• v.27 no.5
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• pp.1155-1168
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• 2016

This paper considers a probability density estimation problem of climate values. In particular, we focus on estimating probability densities of summer extreme temperature over South Korea. It is known that the probability density of climate values at one location is similar to those at near by locations and one doesn't follow well known parametric distributions. To accommodate these properties, we use a mixture of conditional autoregressive species sampling model, which is a nonparametric Bayesian model with a spatial dependency. We apply the model to a dataset consisting of summer maximum temperature and minimum temperature over South Korea. The dataset is obtained from University of East Anglia.

• Journal of Soil and Groundwater Environment
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• v.7 no.1
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• pp.3-14
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• 2002

We analyzed hydrologic time-series data obtained from a fractured aquifer in Wonju and a porous shallow aquifer in Uiwang area. Auto-correlation, spectral density, and cross-correlation functions were used for the analyses. Water level at a shallow well in Wonju was weakly auto-correlated and it was sensitive to direct infiltration from rainfall through soil zone while that at a well screened in the fractured zone showed a relative stability to an outer stress (rainfall), which was derived from a delayed transmission of recharge stress through a fracture network from a remote area. Characteristics of time-series data in Uiwang area were similar to those in the fractured zone in Wonju. This was caused by a regional recharge from a distant area rather than a direct infiltration. This study demonstrated a usefulness of time series analyses for identification of recharge mechanism.

• New Physics: Sae Mulli
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• v.68 no.11
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• pp.1183-1191
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• 2018

The plasmon behaviors in a superlattice of $GaAs/Al_xGa_{1-x}As$ multiple quantum wells with a half-parabolic confining potential due to different dielectric interfaces are studied under magnetic and electric fields perpendicular and parallel to the superlattice axis by using a previously published theoretical framework. From the density-density correlation functions by considering the intrasubband and the inter-subband transitions under the random phase approximation, we calculate the dispersion energies of the surface and the bulk states as functions of the composition of the multiple quantum well structure and of the magnetic field strength and the average electric field strength over the quantum well. The Raman intensities for various magnetic field strengths and average electric field strengths over the quantum well are also obtained as a function of the energy of the incoming light for these states.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.7
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• pp.1085-1094
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• 1999

In the global system for the mobile communication (GSM) system, the class of training sequences used in a TDMA frame is a preamble sequence with a period of 16 bits for the channel impulse response measurement and the start up equalization during the training period. If the transmitted preamble sequence and the binary sequence in the receiver properly satisfy a condition, this training sequences used for fastly adjusting the tap coefficients and impulse response can be measured by calculating the crosscorrelation function. In this paper, it is used that training sequences have zero values of the autocorrelation at all delays except zero and middle shifts. A comparison of convergence rate, a mathematical approach for fast start-up equalization and correctly channel impulse response measurement are proposed.