• Tribology and Lubricants
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• v.35 no.3
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• pp.151-157
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• 2019

Insulated oil degradation produces charged by-products, such as acids and hydro-peroxides, which tend to reduce the insulating properties of the oil. In this study, UV-vis spectroscopy measurement technology is developed and experimentally compared with other measurement methods, such as the titration method and IR spectroscopy, to validate its ability to monitor the degradation of electrical insulating paper. The degradation characteristics of the insulating paper are appropriately represented through various types of measurement methods, such as the Tan (delta) method, $CO_2$ gas production measurement, the titration method, and IR spectroscopy. The results are demonstrated to be well comparable to a change in the fluorescence emission ratio (FER), which is defined as the shift in fluorescence intensity in the measured wavelength range, and also to the chromatic ratio, which is defined as a color shift to longer wavelength ranges. The results also show that, by using UV-vis spectroscopy, it is possible to detect the degradation of the insulating paper. This study suggests that UV-vis spectroscopy can be applied as an alternative to high-performance liquid chromatography, which is the internationally recognized measurement technology for cellulose paper degradation. The FER detector is also verified to be useful as an effective condition-monitoring device for power transformers.

• Journal of Ocean Engineering and Technology
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• v.35 no.4
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• pp.266-272
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• 2021

Mooring systems are among the most important elements employed to control the motion of floating offshore structures on the sea. Considering the use of polymer material, a new method is proposed to address the creep characteristics rather than the method of using a tension load cell for measuring the tension of the mooring line. This study uses a synthetic mooring rope made from a polymer material, which usually consists of three parts: center, eye, and splice, and which makes a joint for two successive ropes. We integrate the optical sensor into the synthetic mooring ropes to measure the rope tension. The different structure of the mooring line in the longitudinal direction can be used to measure the loads with the entire mooring configuration in series, which can be defined as SMART (Smart Mooring and Riser Truncation) mooring. To determine the characteristics of the basic SMART mooring, a SMART mooring with a diameter of 3 mm made of three different polymer materials is observed to change the wavelength that responds as the length changes. By performing the longitudinal tension experiment using three different SMART moorings, it was confirmed that there were linear wavelength changes in the response characteristics of the 3-mm-diameter SMART moorings. A 54-mm-diameter SMART mooring is produced to measure the response of longitudinal tension on the center, eye, and splice of the mooring, and a longitudinal tension of 100 t in step-by-step applied for the Maintained Test and Fatigue Cycle Test is conducted. By performing a longitudinal tension experiment, wavelength changes were detected in the center, eye, and splice position of the SMART moorings. The results obtained from each part of the installed sensors indicated a different strain measurement depending on the position of the SMART moorings. The variation of the strain measurement with the position was more than twice the result of the difference measurement, while the applied external load increased step-by-step. It appears that there is a correlation with an externally generated longitudinal tensional force depending on the cross-sectional area of each part of the SMART mooring.

• Korean Journal of Optics and Photonics
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• v.22 no.2
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• pp.67-71
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• 2011

In the paper, we have demonstrated an azobenzene-coated fiber Bragg grating (FBG) for monitoring ultraviolet light (UV) intensity in remote measurement. The elasticity of the coated azobenzene polymer is changed by the UV light, which induces a center wavelength change corresponding to the change of the FBG's grating period. The wavelength shift resulting from both UV light and other light with the wavelength out of the UV range was about 0.18 nm. In order to improve the accuracy of the measurement, the center wavelength shift caused by radiant heat of the light source was sufficiently removed by using a thermal filter. The amount of the center wavelength shift was consequently reduced to 0.06 nm, compared to the result without the thermal filter. Also, the FBGs coated by using azobenzene polymer were produced by two different methods; thermal casting and UV curing. Considering temperature dependence, UV curing is more suitable than thermal casting in UV sensor application of the azobenzene-coated FBG. In addition, we have confirmed the wavelength dependence of the optical sensor by means of four different band pass filters. Thus, we found out that the center wavelength shift per unit intensity is 0.029 [arb. unit] as a maximum value at 370 nm wavelength region and that the absorption spectrum of the azobenzene polymer was very consistent with the wavelength dependence of the azobenzene-coated FBG.

• Korean Journal of Remote Sensing
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• v.40 no.3
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• pp.275-284
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• 2024

Monitoring crop growth changes and water content is crucial in the agricultural sector. This study utilized drones equipped with Short Wavelength Infrared (SWIR) sensors, sensitive to moisture changes, to observe soybeans' growth and water content variations. We confirmed that as soybeans grow more vigorously, their water content increases and differences in irrigation levels lead to decreases in vegetation and moisture indices. This suggests that waterlogging slows down soybean growth and reduces water content, highlighting the importance of detailed monitoring of vegetation and moisture indices at different growth stages to enhance crop productivity and minimize damage from waterlogging. Such monitoring could also preemptively detect and prevent the adverse effects of moisture changes, such as droughts, on crop growth. By demonstrating the potential for early diagnosis of moisture stress using drone-based SWIR sensors, this research suggests improvements in the efficiency of large-scale crop management and increases in yield, contributing to agricultural production.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.8
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• pp.62-67
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• 1999

In this letter, a scheme for increasing the input power dynamic range of wavelength converters based on cross-gain modulation (XGM) in semiconductor optical amplifiers (SOA/s) is proposed. We investigate the effect of input pump and probe powers on the power penalty, the measure of performance for the wavelength converters. As a result, we show that the optimal bit error rate (BER) performance can be obtained when the probe power is kept 3 dB weaker than the pump power. Using this characteristic, we propose the wavelength converter scheme that controls the probe power level by monitoring the input pump power and adjusting the bias current of probe source accordingly. Consequently, the wavelength converter for wide input power dynamic range can be implemented. We show that an input power dynamic range of more than 20 dB at 2.5 Gb/s is achievable.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.1
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• pp.97-109
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• 2007

Vertical distribution and optical properties of atmospheric aerosols above the Korean peninsula are quite important to estimate effects of aerosol on atmospheric environment and regional radiative forcing. For the first time in Korea, vertical microphysical properties of atmospheric aerosol obtained by inversion algorithm were analyzed based on optical data of multi-wavelength Raman lidar system developed by the Advanced Environmental Monitoring Research Center (ADEMRC), Gwangju Institute Science and Technology (GIST). Data collected on 14 June 2004 at Gwangju ($35.10^{\circ}N,\;126.53^{\circ}E$) and 27 May 2005 at Anmyeon island ($36.32^{\circ}N,\;126.19^{\circ}E$) were used as raw optical data for inversion algorithm. Siberian forest fire smoke and local originated haze were observed above and within the height of PBL, respectively on 14 June 2004 according to NOAA/Hysplit backstrajectory analysis. The inversion of lidar optical data resulted in particle effective radii around $0.31{\sim}0.33{\mu}m$, single scattering albedo between $0.964{\sim}0.977$ at 532 nm in PBL and effective radii of $0.27{\mu}m$ and single scattering albedo between $0.923{\sim}0.924$ above PBL. In the case on 27 May 2005, biomass burning from east China was a main source of aerosol plume. The inversion results of the data on 27 May 2005 were found to be particle effective radii between $0.23{\sim}0.24{\mu}m$, single scattering albedo around $0.924{\sim}0.929$ at 532 nm. Additionally, the inversion values were well matched with those of Sun/sky radiometer in measurement period.

• Korean Journal of Remote Sensing
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• v.36 no.5_4
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• pp.1231-1244
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• 2020

Landsat satellites are representative optical satellites that have observed the Earth's surface for a long-term, and are suitable for long-term changes such as disaster preparedness/recovery monitoring, land use change, change detection, and time series monitoring. In this paper, clouds and cloud shadows were detected using QA bands to detect and remove clouds simply and efficiently. Then, the missing area of the experimantal image is restorated through the SSG algorithm, which does not directly refer to the pixel value of the reference image, but performs restoration to the pixel value in the Experimental image. Through this study, we presented the possibility of utilizing the modified SSG algorithm by quantitatively and qualitatively evaluating information on variousl and cover conditions in the thermal wavelength band as well as the visible wavelength band observing the surface.

• Membrane Journal
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• v.21 no.2
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• pp.171-176
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• 2011

Membrane fouling is formed due to pore blocking and cake formation by suspended material or contaminant in the membrane boundary layer. Membrane fouling is main obstacle for the wider application of industrial water treatment. The objective of this paper is to study the direct monitoring technique for the measuring the membrane fouling in real time. We investigated the extracted image of R, G, and B by visible light irradiation of 360 nm wavelength to measure the membrane fouling in real time by transparent foulant. The intensity of B of 400~499 nm wavelength range was stronger than that of R and G. The fluorescence image extraction analysis appeared to be a very attractive technique for monitoring the membrane fouling in real time.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.7
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• pp.54-60
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• 2007

We constructed a fiber-optic temperature sensor system using a sensor array with 15 fiber Bragg gratings for distributed temperature monitoring in electrical power systems. A polynomial fitting algorithm was used to compensate the nonlinear action of the MEMS tuneable wavelength filter used for Bragg wavelength demodulation Fixed passband wavelengths from a Fabry-Perot ITU filter were used as reference wavelengths for the fitting algorithm which obtained constant accuracy regardless of the wavelength scanning range and frequency. About 0.18[%] of linearity error compared to reference thermocouple thermometer has been obtained in the preliminary experimental results.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.7
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• pp.507-514
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• 2003

Inspection and shape measurement of three-dimensional objects are widely needed in industries for quality monitoring and control. Recently the shape measurement using interferometric principle is found to be a successful methodology among other visual or optical technologies. Especially, the measuring method using wavelength scanning interferometer(WSI) has a great advantage in comparison with other conventional jnterferometric methods in that the absolute distance from the reference surface can be directly obtained from the amount of jnterferometric phase change. However, the measurement methods using WSI proposed by other researchers have low measurement resolution so far because they can't measure fractional phase change. To avoid this shortcoming we propose a new algorithm in this paper, which can obtain a small amount of even fractional phase change by sinusoidal function fitting. To evaluate the effectiveness of the proposed sinusoidal function fitting algorithm, a series of measuring experiments are conducted for discontinuously shaped specimens which have various height. The proposed algorithm shows much more enhanced measurement resolution than other existing conventional algorithms such as zero crossing algorithm and Fourier transform algorithm.