• Korean Journal of Remote Sensing
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• v.31 no.2
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• pp.101-110
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• 2015

Synthetic Aperture Radar Interferometry (InSAR) is affected by various noise source such as atmospheric artifact, orbital error, processing noise etc.. Especially, one of the dominant noise source for long-wave SAR system, such as ALOS PALSAR (L-band SAR satellite) is the ionosphere effect because phase delays on radar pulse through the ionosphere are proportional to the radar wavelength. To avoid misinterpret of phase signal in the interferogram, it is necessary to detect and correct ionospheric errors. Recently, a MAI (Multipler Aperture SAR Interferometry) based ionospheric correction method has been proposed and considered one of the effective method to reduce phase errors by ionospheric effect. In this paper, we introduce the MAI-based method for ionospheric correction. Moreover we propose an efficient method that apply the method over non-coherent area using directional filter. Finally, we apply the proposed method to the ALOS PALSAR pairs, which include the west sea coast region in Korea. A polynomial fitting method, which is frequently adopted in InSAR processing, has been applied for the mitigation of phase distortion by the orbital error. However, the interferogram still has low frequency of Sin pattern along the azimuth direction. In contrast, after we applied the proposed method for ionospheric correction, the low frequency pattern is mitigated and the profile results has stable phase variation values within ${\pm}1rad$. Our results show that this method provides a promising way to correct orbital and ionospheric artifact and would be important technique to improve the accuracy and the availability for L-band or P-band systems.

• Korean Journal of Remote Sensing
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• v.34 no.2_2
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• pp.313-326
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• 2018

This paper introduces core techniques on ship detection and tracking based on a compact HF radar platform which is necessary to establish a wide-area surveillance network. Currently, most HF radar sites are primarily optimized for observing sea surface radial velocities and bearings. Therefore, many ship detection systems are vulnerable to error sources such as environmental noise and clutter when they are applied to these practical surface current observation purpose systems. In addition, due to Korea's geographical features, only compact HF radars which generates non-uniform antenna response and has no information on target information are applicable. The ship detection and tracking techniques discussed in this paper considers these practical conditions and were evaluated by real data collected from the Yellow Sea, Korea. The proposed method is composed of two parts. In the first part, ship detection, a constant false alarm rate based detector was applied and was enhanced by a PCA subspace decomposition method which reduces noise. To merge multiple detections originated from a single target due to the Doppler effect during long CPIs, a clustering method was applied. Finally, data association framework eliminates false detections by considering ship maneuvering over time. According to evaluation results, it is claimed that the proposed method produces satisfactory results within certain ranges.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.4
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• pp.491-498
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• 2012

Recently, many papers have been proposed in order to improve the OFDM system performance in T-DMB DOCR (Digital On Channel Repeater), by using removing the feedback signal so that the transmitter power can be increased or by using the equalizer to remove ICI. Despite these efforts, however, signal quality at the receiving terminal has not been improved because of constellation smearing in T-DMB DOCR. In this paper, in order to suppress constellation smearing, we propose an effective equalizer algorithm that can improve system performance. We perform adaptive channel estimation and non-coherent decision directed noise cancellation method that can estimate the channel subsequently during data symbols period in the frequency domain. So we can obtain better quality of the signal at the receiving terminal. In order to secure QoS(Quality of Service) required in T-DMB handsets, we evaluate SNR and BER in T-DMB DOCR(Digital On Channel Repeater) and verified by simulation. In this simulation results, this system is satisfied the performance of BER=$10^{-5}$ at less than SNR=14 dB at the receiver after compensation of phase noise -18 dBc.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.8
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• pp.1-10
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• 2000

Performance analyses of hybrid DS-SFH spread-spectrum systems using coherent MSK and QPSK modulation techniques are considered over Rayleigh fading channel in the presence of multi-tone jamming. The BER equations for MSK and QPSK systems with non-diversity reception in the receiver are derived as the concept of average signal-to-noise power ratio E$\_$b//N$\_$0/ and jamming-to-signal power ratio JSR, and the performances is evaluated for various system parameters. The evaluation of performance is done between fading and nonfading system, and between MSK and QPSK system. Results show that the performances of two systems are similar in low JSR. However, MSK system outperforms QPSK system as JSR increases. Overall performances of two systems are a little improved as the DS spreading gain increases for the total spread-spectrum bandwidth fixed. The performance difference between fading system and nonfading system is similar in low E$\_$b//N$\_$0/, however, it becomes very largewith increase of E$\_$b//N$\_$0/..

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2386-2396
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• 1996

A numerical simulation has been performed for isothermal and reacting flows in an exisymmetric, bluff-body research combustor. The present formulation is based on the density-weighted averaged Navier-Stokes equations together with a k-epsilon. turbulence model and a modified eddy-breakup combustion model. The PISO algorithm is employed for solution of thel Navier-Stokes system. Comparison between measurements and predictions are made for a centerline axial velocities, location of stagnation points, strength of recirculation zone, and temperature profile. Even though the numerical simulation gives acceptable agreement with experimental data in many respects, the present model is defictient in predicting the recoveryt rate of a central near-wake region, the non-isotropic turbulence effects, and variation of turbulent Schmidt number. Several possible explanations for these discrepancies have been discussed.

• Applied Microscopy
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• v.38 no.4
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• pp.279-284
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• 2008

The phase change materials have been extensively used as an optical rewritable data storage media utilizing their phase change properties. Recently, the phase change materials have been spotlighted for the application of non-volatile memory device, such as the phase change random access memory. In this work, we have investigated the crystallization behavior and microstructure analysis of In-Sb-Te (IST) thin films deposited by RF magnetron sputtering. Transmission electron microscopy measurement was carried out after the annealing at $300^{\circ}C$, $350^{\circ}C$, $400^{\circ}C$ and $450^{\circ}C$ for 5 min. It was observed that InSb phases change into $In_3SbTe_2$ phases and InTe phases as the temperature increases. It was found that the thickness of thin films was decreased and the grain size was increased by the bright field transmission electron microscopy (BF TEM) images and the selected area electron diffraction (SAED) patterns. In a high resolution transmission electron microscopy (HRTEM) study, it shows that $350^{\circ}C$-annealed InSb phases have {111} facet because the surface energy of a {111} close-packed plane is the lowest in FCC crystals. When the film was heated up to $400^{\circ}C$, $In_3SbTe_2$ grains have coherent micro-twins with {111} mirror plane, and they are healed annealing at $450^{\circ}C$. From the HRTEM, InTe phase separation was occurred in this stage. It can be found that $In_3SbTe_2$ forms in the crystallization process as composition of the film near stoichiometric composition, while InTe phase separation may take place as the composition deviates from $In_3SbTe_2$.