• Journal of Korean Society for Atmospheric Environment
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• v.14 no.3
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• pp.229-236
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• 1998

Visibility is a good indicator of comprehensive alto quality. The prevailing visibility in Seoul is no better than the past although the average concentration of SO2 and TSP (total suspended particulate) has decreased quite significantly in the past decade, owing to the government efforts to reduce the emission. Then, a question arises why visibility has not been improved. In order to answer this question we have investigated which components of air pollutants are most responsible for the visibility degradation in Seoul. Analysis on the visibility vs the aerosol sixte distribution measured by an optical particle counter shows that the particles of the size interval between 0.5mm and 2.5mm are most responsible for the visibility degradation. Among the criteria air Pollutants, NOB concentration is found to be moot responsible, rather than PM10. ton analysis of the particulate collected by a high volume sampler shows that the nitrate component increases more significantly than other ions when visibility becomes very poor. Therefore, we conclude that the major causes of visibility degradation in Seoul are the increase of NOB, nitrates and the particles of the size range between 0.5mm and 2.5mm.

• Journal of Korean Society for Atmospheric Environment
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• v.18 no.6
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• pp.503-514
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• 2002

During the past two decades, primary pollutants in the ambient air have been substantially reduced in Korea by aggressive government efforts such as the switchover to clean fuels and equipment of automobiles with a three-way catalytic converter. However, visibility impairment in Seoul and major metropolitan areas has been a stubborn problem. It is apparent that both directly emitted fine particles mainly from vehicles and secondary fine particles from photochemical reactions could contribute to this visibility impairment. In addition, Korea is located downwind of the prevailing westerlies from China and is influenced by the emissions of air pollutants in China. In order to assess this complicated problem of visibility impairment, the visibility trends for the past 17 years observed at more than 60 stations throughout the country were analyzed. The results showed that visibilities were generally the lowest in the winter morning in comparison with those in the summer afternoon as well as the annual average values. It was believed that primary pollution was principally responsible for visibility impairment in most areas. The visibility in the summer afternoon was lower in clean coastal areas along with a high level of relative humidity due to the inflow of moist air accompanied by sea breeze. Although contributions of secondary particles from photochemical reactions and long-range transport of fine particles to the visibility impairment were probable, their certain evidences were not found.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.6
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• pp.1-7
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• 2007

In this paper, It evaluated visibility about Metal Halide Lamp(MHL), High Pressure Sodium Lamp(HPS) and PLS(Plasma Lighting System) as Road lighting source in fog conditions. To evaluate visibility, it analyzed valuation of subjects about each light sources in special fog conditions. In result, it obtained that High Pressure Sodium Lamp has best visibility in photopic vision and PLS has best visibility in scotopic vision. This result is expected to help about select of Road lighting source.

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.2
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• pp.167-177
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• 2003

The number size distribution of urban aerosols ranging from 0.02 to 20 ${\mu}{\textrm}{m}$ in diameter was measured by using a scanning mobility particle sizer (SMPS) system and an aerodynamic particle sizer spectrometer (APS) at Seoul from November 30,2001 to January 14, 2002. The gaseous species such as CO, NO, NO$_2$, and $O_3$ were also continuously monitored. The daily average concentration of urban aerosols sorted into three groups (0.02~0.1 ${\mu}{\textrm}{m}$, 0.1~1 ${\mu}{\textrm}{m}$ and 1~10 ${\mu}{\textrm}{m}$) and the typical number, surface, and volume distributions of urban aerosols were discussed in this paper. The weekly variation of aerosol concentration was compared with those of gaseous concentrations. relative humidity, and visibility. The results showed that the particle number concentration seemed to increase in the morning and the number concentration of fine particles less than 1 fm in diameter seemed to increase when the concentrations of CO, NO, and NO$_2$ were high. The number concentration of fine particles was relatively high when the relative humidity was greater than 70％ during the increasing period of relative humidity. The visibility was weakly correlated with the concentration of aerosols ranging 0.1 to 1 ${\mu}{\textrm}{m}$, and the number size distribution for high visibility episode was apparently different from that for low visibility episode.

• Korean Journal of Remote Sensing
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• v.37 no.1
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• pp.97-110
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• 2021

Fog can cause large-scale human and economic damages, including traffic systems and agriculture. So, Korea Meteorological Administration is operating about 290 visibility meters to improve the observation level of fog. However, it is still insufficient to detect very localized fog. In this study, high-resolution grid-type visibility data were retrieved from irregularly distributed visibility data across the country. To this end, three objective analysis techniques (Inverse Distance Weighting (IDW), Ordinary Kriging (OK) and Universal Kriging (UK)) were used. To find the best method and parameters, sensitivity test was performed for the effective radius, power parameter and variogram model that affect the level of objective analysis. Also, the effect of data distribution characteristics (level of normality) on the performance level of objective analysis was evaluated. IDW showed a relatively high level of objective analysis in terms of bias, RMSE and correlation, and the performance is inversely proportional to the effective radius and power parameter. However, the two Krigings showed relatively low level of objective analysis, in particular, greatly weakened the variability of the variables, although the level of output was different depending on the variogram model used. As the level of objective analysis is greatly influenced by the distribution characteristics of data, power, and models used, care should be taken when selecting objective analysis techniques and parameters.

• Journal of The Korean Astronomical Society
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• v.39 no.2
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• pp.51-56
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• 2006

We report the development of a semi-VLBI observation system operating at 21 cm and present the measurement of visibility function toward the sun using this system. The system consists of two 2.3 meter antennas with a maximum separation of 35 meter, a conventional high speed data acquisition system, and a set of programs for software correlation. Since two local oscillators of receiver modules are independent, data had to be fringe-fitted to yield the visibility amplitude. It is found that the visibility amplitude decreases and then bounces back as baseline increases. We confirm that solar disk with brighter limb best explains the measured visibility amplitude.

• Current Optics and Photonics
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• v.1 no.3
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• pp.186-195
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• 2017

Obtaining accurate visibility measurements is a common atmospheric optical problem, and of vital significance to civil aviation. To effectively evaluate and improve the accuracy of visibility measurements, an outdoor atmospheric simulation chamber with dimensions of $1.8{\times}1.6{\times}55.7m^3$ was constructed. The simulation chamber could provide a relatively homogeneous haze environment, in which the visibility varied from 10 km to 0.2 km over 5 hours. A baseline-changing visibility measurement system was constructed in the chamber. A mobile platform (receiver) was moved from 5 m to 45 m, stopping every 5 m, to measure and record the transmittance. The total least-squares method was used to fit the extinction coefficient. During the experiment conducted in the chamber, the unit weight variance was as low as $1.33{\times}10^{-4}$ under high-visibility conditions, and the coefficient of determination ($R^2$) was as high as 0.99 under low-visibility conditions, indicating high stability and accuracy of the system used to measure the extinction coefficients and strong consistency between repeated measurements. A Grimm portable aerosol spectrometer (PAS) was used to record the aerosol distribution, and then Mie theory was used to calculate the extinction coefficients. The theoretical results were found to be consistent with the measurements and exhibited a positive correlation, although they were higher than the measured values.

• Journal of the Optical Society of Korea
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• v.14 no.2
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• pp.121-126
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• 2010

We analyze image visibility of a projection-type integral imaging system without diffuser, in terms of the fill factor, which is determined by the relationship between the exit pupil of the projection system and the size and the focal length of the elemental lens. High fill factor is a requirement for good visibility. Moreover, for psychological reasons, for the same fill factor, better visibility is accomplished using a relatively small elemental lens. In this paper, we study image visibility through basic experiments and results.

• Journal of Astronomy and Space Sciences
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• v.27 no.3
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• pp.195-204
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• 2010

The optimal Earth-Moon transfer trajectory considering spacecraft's visibility from the Daejeon ground station visibility at both the trans lunar injection (TLI) and lunar orbit insertion (LOI) maneuvers is designed. Both the TLI and LOI maneuvers are assumed to be impulsive thrust. As the successful execution of the TLI and LOI maneuvers are crucial factors among the various lunar mission parameters, it is necessary to design an optimal lunar transfer trajectory which guarantees the visibility from a specified ground station while executing these maneuvers. The optimal Earth-Moon transfer trajectory is simulated by modifying the Korean Lunar Mission Design Software using Impulsive high Thrust Engine (KLMDS-ITE) which is developed in previous studies. Four different mission scenarios are established and simulated to analyze the effects of the spacecraft's visibility considerations at the TLI and LOI maneuvers. As a result, it is found that the optimal Earth-Moon transfer trajectory, guaranteeing the spacecraft's visibility from Daejeon ground station at both the TLI and LOI maneuvers, can be designed with slight changes in total amount of delta-Vs. About 1% difference is observed with the optimal trajectory when none of the visibility condition is guaranteed, and about 0.04% with the visibility condition is only guaranteed at the time of TLI maneuver. The spacecraft's mass which can delivered to the Moon, when both visibility conditions are secured is shown to be about 534 kg with assumptions of KSLV-2's on-orbit mass about 2.6 tons. To minimize total mission delta-Vs, it is strongly recommended that visibility conditions at both the TLI and LOI maneuvers should be simultaneously implemented to the trajectory optimization algorithm.

• Journal of the Semiconductor & Display Technology
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• v.16 no.4
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• pp.36-40
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• 2017

With an attempt to enhance the visibility of laser beam, we have investigated a black matrix with scattering particles by ray tracing simulations. As the scattering particle density is increased, the detected power by the receiver is increased, thereby enhancing the visibility. In reality, the visibility is reduced with increasing incident angle (away from the normal incidence) of laser beam, a phenomenon also observed by ray tracing simulations. It is due to the fact that the mean path is increased within a highly absorptive BM layer or a smaller number of rays hit the BM area when the incident angle is high. Embedding a number of scattering particles into BM may bring in crosstalk among pixels. However, it is negligible because scattered rays inside highly absorptive BM are re-scattered due to the high scattering particle density, decreasing the power of scattered rays into the active areas.