• Journal of the Institute of Convergence Signal Processing
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• v.8 no.3
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• pp.185-191
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• 2007

Remote sensing images are multispectral image data collected from several band divided by wavelength ranges. The classification of remote sensing images is the method of classifying what has similar spectral characteristics together among each pixel composing an image as the important algorithm in this field. This paper presents a pattern classification method of remote sensing images by applying a possibilistic fuzzy c-means (PFCM) algorithm. The PFCM algorithm is a hybridization of a FCM algorithm, which adopts membership degree depending on the distance between data and the center of a certain cluster, combined with a PCM algorithm, which considers class typicality of the pattern sets. In this proposed method, we select the training data for each class and perform supervised classification using the PFCM algorithm with spectral signatures of the training data. The application of the PFCM algorithm is tested and verified by using Landsat TM and IKONOS remote sensing satellite images. As a result, the overall accuracy showed a better results than the FCM, PCM algorithm or conventional maximum likelihood classification(MLC) algorithm.

• Journal of Korean Society for Geospatial Information Science
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• v.20 no.4
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• pp.135-143
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• 2012

Remote sensing which observes repeatedly the whole Earth and GIS-based decision-making technology have been utilized widely in disaster management such as early warning monitoring, damage investigation, emergent rescue and response, rapid recovery etc. In addition, various countermeasures of national level to collect timely satellite imagery in emergency have been considered through the operation of a satellite with onboard multiple sensors as well as the practical joint use of satellite imagery by collaboration with space agencies of the world. In order to respond heavy snowfall disaster occurred on the east coast of the Korean Peninsula in February 2011, snow-covered regions were analyzed and detected in this study through NDSI(Normalized Difference Snow Index) considering reflectance of wavelength for MODIS sensor and change detection algorithm using satellite imagery collected from International Charter. We present the application case of National Disaster Management Institute(NDMI) which supported timely decision-making through GIS spatial analysis with various spatial data and snow cover map.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.8B
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• pp.514-524
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• 2005

In optical burst switching(OBS) networks, the ingress edge router assembles packets in the same class queue into the appropriate size of burst. A burst control packet(BCP) is generated for channel reservation of corresponding data burst and sent earlier than the corresponding data burst with an offset time. Offset time is determined considering the number of hops from source to destination and the required quality of service(QoS). After offset time, the burst data is passed through tile pre-configured optical switches without any O/E/O conversion. But a failure in OBS networks may lead to the loss of bursts until the ingress nodes receive the failure indication signal. This results in a significant degradation in QoS. Therefore, in this paper, we propose a fault-tolerant node architecture based on sub-carrier multiplexing to reduce the effects of failure in OBS networks. The Performance of the proposed fault-tolerant node architecture exhibits considerable improvement as compared with the previous ones.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.3
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• pp.664-674
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• 1996

In high speed multi-wavelength networks, retransmission overhead due to desination conflict or control packet collision is one factor of performance degration because signal prpagation delay is much larger than the transmission time of data packet. In this paper, an efficient WDMA protocol with a collision avoidance mechanism is proposed for high speed WDM single-hop network with a passive star topology. In proposed protocol, each node has cource queues and routing table to store souting informatio. This architecture makes is possible to avoid any kind of collision when a node reserves the channel to transmit a data packet. High system thoughput and channel utilization can be achieved by proposed protocol since there are no discarded packets caused by any collision at transmission time. The performance of proposed protocol is evaluated in term of throughput and delay with variations in offered load. Simulation results show that the proposed protocol has superior performance to convertional protocols under nonuniform traffic as well as uniform traffic.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12B
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• pp.1433-1441
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• 2011

Design rules of optical transmission links with dispersion management (DM) and optical phase conjugation (OPC) for compensating optical signal distortion due to chromatic dispersion and self phase modulation (SPM) of single mode fiber (SMF) are investigated in this paper. Design rules consist of optimal net residual dispersion (NRD) and optimal range of launching power of wavelength division multiplexed (WDM) channels as a function of total transmission length and span length. In all considered total transmission length and span length, optimal NRD are obtained to +10 ps/nm and -10 ps/mn for transmission links, which is controlled by precompensation and postcompensation, respectively. It is confirmed that system performances are more improved and effective NRD for wide launching power have wider range as total transmission length and span length are more decreased.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.25-30
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• 2017

Millimeter wave (mmWave) bands are expected to improve date rate of 5G systems due to the wide available bandwidth. While severe path loss in those bands has impeded the utilization, short wavelength enables a large number of antennas packed in a compact form, which can mitigate the path loss. However, estimating the channel with a conventional scheme requires a huge training overhead, hence an efficient estimation scheme operating with a small overhead needs to be developed. The sparsity of mmWave channels caused by the limited scatterers can be exploited to reduce the overhead by utilizing compressed sensing. In this paper, we introduce compressed sensing techniques for mmWave channel estimation. First, we formulate wideband channel estimation into a sparse recovery problem. We also analyze the characteristics of random measurement matrix constructed using quantized phase shifters in terms of mutual incoherence.

• Aerospace Engineering and Technology
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• v.10 no.2
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• pp.154-162
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• 2011

The KOrea Multi-Purpose Satellite-3 (KOMPSAT-3) provides 0.7 m Ground Sample Distance (GSD) panchromatic image and 2.8 m GSD multi-spectral image data for various applications. The KOMPSAT-3 system data will be applied in the field of earth observations, covering land, sea, coastal zones, and Geographic Information Systems (GIS). In order to keep the swath width of 15km at nadir view of KOMPSAT-3, CCD consist of approximately 24,020 pixels excluding 20 dark pixels at both sides and has overlap region. Because there are no CCD-line sensors with a pixel size of $7{\mu}m$, the field of view is separated into 2 parts and imaged on 2 detectors, each with 12,080 pixels. Therefore, 2 detectors have different geometric characteristic. This paper provides image simulation for geometric characteristics analysis of overlapping area of KOMPSAT-3 using KOMPSAT-2 image data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.3
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• pp.32-38
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• 2005

FBG sensors have been studied more actively than any other fiber optic sensor because of good multiplexing capabilities among many fiber optic sensors. The demodulation method of FBG sensors is based on the detection of wavelength shift of their sensor peaks and properties such as strain and temperature can be measured by detecting them. However, the signal stability of FBG sensors can be influenced by the strain gradient induced by structural geometry or cracks on the surface when FBG sensors are embedded into or attached on the structure. In this study, the signal characteristics of reflected spectra of FBG sensors under strain gradient were verified and the relations between the grating length of FBG sensors and the amount of strain gradient were investigated. From the experimental results, the recommended working range of FBG sensors under strain gradients was shown quantitatively with respect to grating lengths of them.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.1
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• pp.1-7
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• 2004

The angular dependence (or profile) of backscattered ultrasound was measured for steel specimens with a range of surface roughness, $1{\sim}71{\mu}m$. Backscattering profiles at or near the Rayleigh angle still showed roughness dependence while the assessment of surface roughness via normal profile became impossible due to the paint layer masking the roughness. The peak amplitude directly radiated at the Rayleigh angle was proportional to the surface roughness, while the averaged peak amplitude radiated from the backward propagating Rayleigh wave, produced by reflection at a corner, was inversely proportional. In the painted specimens, the linearity of direct backward radiation with the roughness was observed even at the roughness of less than three hundredths of a wavelength, and the abnormal multiple bark reflection caused by periodic roughness disappeared.

• Korean Journal of Remote Sensing
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• v.24 no.6
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• pp.631-639
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• 2008

This study presents an approach to synthesize hyperspectral images of lower resolution at a higher resolution using the high resolution images acquired from a sensor of commercial satellites. The proposed method was applied to the reconstruction of EO-1 Hyperion images using the images acquired from IKONOS sensor. Based on the FitPAN-Mod pansharpening technique (Lee, 2008b), the hyperspectral images of 30m resolution were reconstructed at 1m resolution of IKONOS panchromatic image. In this study, the synthesized hyperspectral images of 50 bands, whose wavelengths range in the wavelength of panchromatic sensor, were generated from the three stages of high resolution reconstruction using FitPAN-Mod. The experimental results show that the proposed method effectively integrates the spatial detail of the panchromatic modality as well as the spectral detail of the hyperspectral one into the synthesized image. It indicates the proposed method has a potential as a technique to produce alternative images for the images that would have been observed from a hyperspectral sensor at the high resolution of commercial satellite images.