• Journal of the Korean GEO-environmental Society
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• v.24 no.2
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• pp.31-40
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• 2023

We installed temporary strong motion seismometers at the ground surface, 1 m, 2 m, and 9 m at an existing seismic station that houses permanent seismometers installed at 20 m and 100 m, to investigate the influence of installation depth on the recorded ambient and anthropogenic noise level and the characteristics of earthquake signals. Analysis of the ambient noise shows that anthropogenic noise dominates where vibration period T < 1 s at the studied site, whereas wind speed appears to be strongly correlated with the noise level at T > 1 s. Frequency-wavenumber analysis of 2D seismometer array suggests that ambient noise in short periods are predominantly body waves, rather than surface waves. The level of ambient noise was low at 9 m and 20 m, but strong amplification of noise level at T < 0.1 s was observed at the shallow seismometers. Both the active-source test result and the recorded earthquake data demonstrated that the signal level is decreased with the increase of depth. Our result also shows that recorded motions at the ground and 1 m are strongly amplified at 20 Hz (T = 0.05 s), likely due to the resonance of the 3 m thick soil layer. This study demonstrates that analysis of ambient and active-source vibration may help find optimal installation depth of strong motion seismometers. We expect that further research considering various noise environments and geological conditions will be helpful in establishing a guideline for optimal installation of strong motion seismometers.

• Journal of Environmental Science International
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• v.11 no.2
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• pp.111-120
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• 2002

Asian dust(or yellow sand) occurs mainly in spring and occasionally in winter in east Asia, when the weather conditions are under an upper trough/cut-off low and surface high/low pressure system during blocking episode days associated with the stationary patterns of the upper level jet stream. The transport mechanism for Asian dust during the blocking episode days in spring 2001 was analyzed using the TOMS aerosol index and meteorological mesoscale model 5(MM5). Based on the E vector, an extension of an Eliassen-Palm flux, the blocking episode days were found to be associated with the development of an upper cut-off low and surface cyclones. Concurrently, the occurrence of dust storms was also determined by strong cold advection at the rear of a jet streak, which exhibited a maximum wind speed within the upper jet stream. As such, the transport mechanism for Asian dust from China was due to advection of the isentropic potential vorticity(IPV) and isentropic surfaces associated with tropopause folding. The transport heights for Asian dust during the blocking episode days were found to be associated with the distribution of the isentropes below the IPV At the same time, lee waves propagated by topography affected the downward motion and blocking of Asian dust in China. The Asian dust transported from the dust source regions was deposited by fallout and rain-out with a reinforcing frontogenesis within a surface cyclone, as determined from satellite images using TOMS and GMS5. Accordingly, these results emphasize the importance of forecasting jet streaks, the IPV, and isentropes with geopotential heights in east Asia.

• Journal of Wetlands Research
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• v.21 no.4
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• pp.281-289
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• 2019

In this study, the typhoon damage forecasting model was developed for southern inland district. The typhoon damage in the inland district is caused by heavy rain and strong winds, variables are many and varied, but the damage data of the inland district are not enough to develop the model. The hydrological data related to the typhoon damage were hour maximum rainfall amount which is accumulated 3 hour interval, the total rainfall amount, the 1-5 day anticipated rainfall amount, the maximum wind speed and the typhoon center pressure at latitude 33° near the Jeju island. The Multivariate Analysis such as cluster Analysis considering the lack of damage data and principal component analysis removing multi-collinearity of rainfall data are adopted for the damage forecasting model. As a result of applying the developed model, typhoon damage estimated and observed values were up to 2.2 times. this is caused it is difficult to estimate the damage caused by strong winds and it is assumed that the local rainfall characteristics are not considered properly measured by 69 ASOS.

• Current Optics and Photonics
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• v.7 no.3
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• pp.237-247
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• 2023

In middle- and long-distance imaging systems, due to the atmospheric turbulence caused by temperature, wind speed, humidity, and so on, light waves propagating in the air are distorted, resulting in image-quality degradation such as geometric deformation and fuzziness. In remote sensing, astronomical observation, and traffic monitoring, image information loss due to degradation causes huge losses, so effective restoration of degraded images is very important. To restore images degraded by atmospheric turbulence, an image-restoration method based on improved compound multibranch feature fusion (CMFNetPro) was proposed. Based on the CMFNet network, an efficient channel-attention mechanism was used to replace the channel-attention mechanism to improve image quality and network efficiency. In the experiment, two-dimensional random distortion vector fields were used to construct two turbulent datasets with different degrees of distortion, based on the Google Landmarks Dataset v2 dataset. The experimental results showed that compared to the CMFNet, DeblurGAN-v2, and MIMO-UNet models, the proposed CMFNetPro network achieves better performance in both quality and training cost of turbulent-image restoration. In the mixed training, CMFNetPro was 1.2391 dB (weak turbulence), 0.8602 dB (strong turbulence) respectively higher in terms of peak signal-to-noise ratio and 0.0015 (weak turbulence), 0.0136 (strong turbulence) respectively higher in terms of structure similarity compared to CMFNet. CMFNetPro was 14.4 hours faster compared to the CMFNet. This provides a feasible scheme for turbulent-image restoration based on deep learning.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.11a
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• pp.81-87
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• 2004

It includes the considerable concentration and dangerousness as the peculiar work of a pilot and dock-master to berthing/deberthing the big object as for the ship within the port or the ship yard. A tug utilization is getting increased in this berthing/deberthing work and the own ship is affected a lot by external force due to moving with low advance speed. In this study, we constructed the 2 dimension virtual system which can conduct the berthing/deberthing manoeuvring work by using mainly tugs in a external force, particularly strong wind. Also, propose objective standard that could estimate the degree of manoeuvring difficulty, and conducted simulation experiment for this. we analyzed correlations between the subjective estimation which is described numerically the decreased dangerousness and the objective index which is related to the main parameter regarding manoeuvring by using this simulator from the result of conducting simulation experiment. And then we discussed the estimation technique of manoeuvring difficulty.

• Journal of Navigation and Port Research
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• v.29 no.3 s.99
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• pp.189-194
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• 2005

The berthing/deberthing manoeuvring operation is the peculiar work owned to the marine pilot and the dock master. So, in the port or the shipyard, the berthing/deberthing manoeuvring operation requires considerable concentration and bears dangerousness. In that situation, a tug utilization is getting increased and the external forces have an effect on the own ship because of moving with low advance speed. In this study, we constructed the 2-dimensional virtual ship manoeuvring simulator system with which we can carry out the berthing/deberthing manoeuvring operation by using tugs in the external forces such as strong wind. And then, we propose the objective indexes by which the degree of manoeuvring difficulty evaluated. Using the present system, we carry out manoeuvring simulation experiment in order to grasp correlation between the objective indexes proposed here and the def{ree of manoeuvring difficulty felt by operator. Lastly, we discuss the evaluation technique of manoeuvring difficulty.

• Atmosphere
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• v.26 no.2
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• pp.257-275
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• 2016

Asian dust is a seasonal meteorological phenomenon influencing most East Asia, irregularly occurring during spring. Unusual heavy Asian dust event in winter was observed in Seoul, Korea, with up to $1,044{\mu}g\;m^{-3}$ of hourly mean $PM_{10}$, in 22~23 February 2015. Causes of such infrequent event has been studied using both ground based and spaceborne observations, as well as numerical simulations including ECMWF ERA Interim reanalysis, NOAA HYSPLIT backward trajectory analysis, and ADAM2-Haze simulation. Analysis showed that southern Mongolia and northern China, one of the areas for dust origins, had been warm and dry condition, i.e. no snow depth, soil temperature of ${\sim}0^{\circ}C$, and cumulative rainfall of 1 mm in February, along with strong surface winds higher than critical wind speed of $6{\sim}7.5m\;s^{-1}$ during 20~21 February. While Jurihe, China, ($42^{\circ}23^{\prime}56^{{\prime}{\prime}}N$, $112^{\circ}53^{\prime}58^{{\prime}{\prime}}E$) experienced $9,308{\mu}g\;m^{-3}$ of hourly mean surface $PM_{10}$ during the period, the Asian dust had affected the Korean Peninsula within 24 hours traveling through strong north-westerly wind at ~2 km altitude. KMA issued Asian dust alert from 1100 KST on 22nd to 2200 KST on 23rd since above $400{\mu}g\;m^{-3}$ of hourly mean surface $PM_{10}$. It is also important to note that, previously to arrival of the Asian dust, the Korean Peninsula was affected by anthropogenic air pollutants ($NO_3^-$, $SO_4^{2-}$, and $NH_4^+$) originated from the megacities and large industrial areas in northeast China. In addition, this study suggests using various data sets from modeling and observations as well as improving predictability of the ADAM2-Haze model itself, in order to more accurately predict the occurrence and impacts of the Asian dust over the Korean peninsula.

• Journal of Korea Water Resources Association
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• v.42 no.2
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• pp.117-129
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• 2009

Evaporation over the world is expected to increase owing to increase in temperature by global warming. However, pan evaporation around the world has decreased in the past few decades. This study, which has been conducted in 18 meteorological gauging stations in Korean peninsula, investigates the changes in pan evaporation and climate variables such as precipitation, temperature, relative humidity, wind speed, sunshine hours, and percentage of sunshine, which can affect evaporation processes; the changes in these variables have been recorded between 1960 and 2007. At most gauging stations, pan evaporation shows statistically significant downward trends. The relative humidity, wind speed, sunshine hours, and percentage of sunshine also show downward trends. On the other hand, precipitation and temperature show upward trends. The spatial distribution of the downward trend in sunshine hours and percentage of sunshine correspond to that of the downward trend in pan evaporation. Scatter plots imply that pan evaporation has a strong positive correlation with the sunshine hours and percentage of sunshine, while it has a negative correlation with precipitation. At the Gangneung gauging station, the open water evaporation estimated using the Penman equation does not show the significant downward trend shown by pan evaporation. This result implies that pan evaporation is not a good indicator of potential or open water evaporations during the investigation of their long-term variability. Finally, this study explains the complementary relationship between pan and actual evaporations. Decreases in the pan evaporation can act as an evidence for the ever-increasing actual evaporation.

• Journal of Korea Water Resources Association
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• v.50 no.11
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• pp.781-793
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• 2017

In this study, applicabilities of aerodynamic approaches for the estimation of pan evaporation were evaluated on 56 study stations in South Korea. To accomplish this study purpose, previous researchers' evaporation estimation equations based on aerodynamic approaches were grouped into seven generalized evaporation models. Furthermore, four multiple linear regression (MLR) models were developed and tested. The independent variables of MLR models are meteorological variables such as wind speed, vapor pressure deficit, air temperature, and atmospheric pressure. These meteorological variables are required for the application of aerodynamic approaches. In order to consider the effect of autocorrelation, MLR models were developed after differencing variables. The applicability of MLR models with differenced variables was compared with that of MLR models with undifferenced variables and the comparison results showed no significant difference between the two methods. The study results have indicated that there is strong correlation between estimated pan evaporation (using aerodynamic models and MLR models) and measured pan evaporation. However, pan evaporation are overestimated during August, September, October, November, and December. Most of meteorological variables that are used for MLR models show statistical significance in the estimation of pan evaporation. Vapor pressure deficit was turned out to be the most significant meteorological variable. The second most significant variable was air temperature; wind speed was the third most significant variable, followed by atmospheric pressure.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.2
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• pp.43-50
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• 2002

This study focused on variability of the sea water temperatures observed off the Dangjin Power Plant in the central west coast of Korea for the period of 1998-1999. Spatial averaged temperature shows the annual range of $20.3^{\circ}C$, with minimum of $3.3^{\circ}C$ in February and maximum of $23.6^{\circ}C$ in August. Horizontal distribution patterns are seasonally reversing: The temperatures are increasing toward inshore of the period of April to October, while they are increasing toward of offshore for the rest of year. Spectral analyses of temperature records show significant peaks at M2 and S2 tidal periods, since the water movement in the study area is influenced by strong tide. The responses of temperature variations to tidal phase show different seasonal characteristics: The temperatures are increasing at flood phases in winter and ebb phases in summer. Amplitudes of the components at M2 and S2 periods are $0.8^{\circ}C\;and\;0.5^{\circ}C$, accounting for 70-80% of daily variation. Coherency analyses between non-tidal components of temperature and wind speed show that in summer, northerly wind components significantly coherent with temperature at 2.8 days period, while in winter, southerly wind component is coherent with 2.4 days period, with 0.6 and 0.7 day phase-lags, respectively.