• Korean Journal of Remote Sensing
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• v.38 no.1
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• pp.83-101
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• 2022

Accurate atmospheric correction is essential for the analysis of land surface and environmental monitoring. Aerosol optical depth (AOD) information is particularly important in atmospheric correction because the radiation attenuation by Mie scattering makes the differences between the radiation calculated at the satellite sensor and the radiation measured at the land surface. Thus, it is necessary to use high-quality AOD data for an appropriate atmospheric correction of high-resolution satellite images. In this study, we examined the Second Simulation of a Satellite Signal in the Solar Spectrum (6S)-based atmospheric correction results for the Sentinel-2 images in South Korea using raster AOD (MODIS) and single-point AOD (AERONET). The 6S result was overall agreed with the Sentinel-2 level 2 data. Moreover, using raster AOD showed better performance than using single-point AOD. The atmospheric correction using the single-point AOD yielded some inappropriate values for forest and water pixels, where as the atmospheric correction using raster AOD produced stable and natural patterns in accordance with the land cover map. Also, the Sentinel-2 normalized difference vegetation index (NDVI) after the 6S correction had similar patterns to the up scaled drone NDVI, although Sentinel-2 NDVI had relatively low values. Also, the spatial distribution of both images seemed very similar for growing and harvest seasons. Future work will be necessary to make efforts for the gap-filling of AOD data and an accurate bi-directional reflectance distribution function (BRDF) model for high-resolution atmospheric correction. These methods can help improve the land surface monitoring using the future Compact Advanced Satellite 500 in South Korea.

• Journal of Astronomy and Space Sciences
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• v.40 no.1
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• pp.1-10
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• 2023

Korea Polar Research Institute (KOPRI) and Korea Astronomy and Space Institute (KASI) have been participating in the European Incoherent Scatter (EISCAT) Scientific Association as an affiliate institution in order to observe the polar ionosphere since 2015. During the period of December 16-21, 2016 and January 3-9, 2018, the observations for the polar ionospheric parameters such as the electron density profiles, ion drift, and electron/ion temperature are carried out in the polar cap/cusp region by the EISCAT Svalbard radar (ESR). The purpose of the observations is to investigate the characteristic of the winter ionosphere in the dayside polar cap/cusp region. In this paper, we briefly report the results of the ESR observations for winter daytime ionosphere and also the simultaneous observations for the ionosphere-thermosphere system together with the balloon-borne instrument High-Altitude Interferometer WIND Experiment (HIWIND) performed by the High Altitude Observatory (HAO), National Center for Atmospheric Research (NCAR). We further introduce our research activities using long-term EISCAT observations for the occurrence of ion upflow and the climatology of the polar ionospheric density profiles in comparison with the mid-latitude ionosphere. Finally, our future research plans will briefly be introduced.

• Korean Journal of Remote Sensing
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• v.39 no.5_3
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• pp.891-907
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• 2023

Compact Advanced Satellite 500-4 (CAS500-4) is scheduled to be launched to collect high spatial resolution data focusing on vegetation applications. To achieve this goal, accurate surface reflectance retrieval through atmospheric correction is crucial. Therefore, a machine learning-based atmospheric correction algorithm was developed to simulate atmospheric correction from a radiative transfer model using Sentinel-2 data that have similarspectral characteristics as CAS500-4. The algorithm was then evaluated mainly for forest areas. Utilizing the atmospheric correction parameters extracted from Sentinel-2 and GEOKOMPSAT-2A (GK-2A), the atmospheric correction algorithm was developed based on Random Forest and Light Gradient Boosting Machine (LGBM). Between the two machine learning techniques, LGBM performed better when considering both accuracy and efficiency. Except for one station, the results had a correlation coefficient of more than 0.91 and well-reflected temporal variations of the Normalized Difference Vegetation Index (i.e., vegetation phenology). GK-2A provides Aerosol Optical Depth (AOD) and water vapor, which are essential parameters for atmospheric correction, but additional processing should be required in the future to mitigate the problem caused by their many missing values. This study provided the basis for the atmospheric correction of CAS500-4 by developing a machine learning-based atmospheric correction simulation algorithm.

• Current Optics and Photonics
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• v.8 no.1
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• pp.38-44
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• 2024

Under the influence of atmospheric turbulence, a star's point image will shake back and forth erratically, and after exposure the originally small star point will spread into a huge spot, which will affect the ground calibration of the star sensor. To analyze the impact of atmospheric turbulence on the positioning accuracy of the star's center of mass, this paper simulates the atmospheric turbulence phase screen using a method based on a sparse spectrum. It is added to the static-star-simulation device to study the transmission characteristics of atmospheric turbulence in star-point simulation, and to analyze the changes in star points under different atmospheric refractive-index structural constants. The simulation results show that the structure function of the atmospheric turbulence phase screen simulated by the sparse spectral method has an average error of 6.8% compared to the theoretical value, while the classical Fourier-transform method can have an error of up to 23% at low frequencies. By including a simulation in which the phase screen would cause errors in the center-of-mass position of the star point, 100 consecutive images are selected and the average drift variance is obtained for each turbulence scenario; The stronger the turbulence, the larger the drift variance. This study can provide a basis for subsequent improvement of the ground-calibration accuracy of a star sensitizer, and for analyzing and evaluating the effect of atmospheric turbulence on the beam.

• Corrosion Science and Technology
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• v.17 no.5
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• pp.231-241
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• 2018

Atmospheric corrosion is generally an electrochemical degradation process of metal. It can be caused by various corrosion factors of atmospheric component, weather, and air pollutants. Moisture, particles of sea salts, and sulfur dioxide are major factors in atmospheric corrosion. Galvanizing coating is one of the most efficient ways to protect iron from corrosion by zinc plating on the surface of the iron. Galvanized steels are being widely used in automobiles, building structures, roofing, and other industrial structures due to their high corrosion resistance compared to bare iron. Atmospheric corrosion of galvanized steel has shown complex corrosion behavior depending on coating process, coating thickness, atmospheric environment, and air pollutants. In addition, different types and kinds of corrosion products can be produced depending on the environment. Lifespan of galvanized steels is also affected by the environment. Therefore, the objective of this study was to determine the corrosion behavior of galvanized steel under atmospheric corrosion at six locations in Korea. When the exposure time was increased, content of zinc from GA surface decreased while contents of iron and oxygen tended to increase. On the other hand, content of iron was constant even after 36 months of exposure of GI.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.2
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• pp.78-84
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• 2016

This paper is focused on the measurement and analysis of an atmospheric electric field which is caused by thunderclouds. The electric field due to thunderclouds changes very slowly. For this reason, the extremely low frequency E-field sensor needs to be used for measuring the atmospheric electric field strength. The balloon-carried E-field sensor system with the time constant of 1sec was designed and fabricated. The electric field sensor consists of $100mm{\times}100mm$ copper plate, active integrator, high pass and low pass filters and batteries. The measurements of atmospheric electric fields were made by the balloon-carried E-field sensor and radiosonde, which sends the data back to ground in real time. From the calibration experiments, the response sensitivity of the E-field sensor was 0.154mV/kV/m in the frequency range of less than 1kHz. As a result from the actual experiment of the atmospheric electric field, the electric field signals were observed from the altitude of about 2.5km. Also, as the altitude was increased, the detected electric field wave oscillated with the fluctuation of sensing plate. The proposed method seems suitable for measurements of atmospheric electric fields, because it is inexpensive, simple to use and launch.

• Journal of Environmental Science International
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• v.14 no.9
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• pp.851-860
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• 2005

In order to how well predict ISCST3(lndustrial Source Complex Short Term version 3) model dispersion of air pollutant at point source, sensitivity was analysed necessary parameters change. ISCST3 model is Gaussian plume model. Model calculation was performed with change of the wind speed, atmospheric stability and mixing height while the wind direction and ambient temperature are fixed. Fixed factors are wind direction as the south wind(l80") and temperature as 298 K(25 "C). Model's sensitivity is analyzed as wind speed, atmospheric stability and mixing height change. Data of stack are input by inner diameter of 2m, stack height of 30m, emission temperature of 40 "C, outlet velocity of 10m/s. On the whole, main factor which affects in atmospheric dispersion is wind speed and atmospheric stability at ISCST3 model. However it is effect of atmospheric stability rather than effect of distance downwind. Factor that exert big influence in determining point of maximum concentration is wind speed. Meanwhile, influence of mixing height is a little or almost not.

• Journal of Environmental Science International
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• v.18 no.8
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• pp.857-865
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• 2009

The physical properties of an atmospheric boundary layer in Wolryong, a west coastal region of Jeju, South Korea, in terms of the atmospheric stability and roughness length, is important and relevant to both engineers and scientists. The study is aiming to understand the atmospheric stability around this region and its effect on the roughness length. We calculate the Monin-Obukhov length(L) against 3 typical regions of the atmospheric condition - unstable regime (-5$-0.2{\leq}H/L{\leq}0.2$) and stable regime (0.2

• Journal of Environmental Science International
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• v.18 no.8
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• pp.899-910
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• 2009

We classified wind sectors according to the wind features in South Korea. In order to get the information of wind speed and wind direction, we used and improved on the atmospheric numerical model. We made use of detailed topographical data such as terrain height data of an interval of 3 seconds and landuse data produced at ministry of environment, Republic of Korea. The result of simulated wind field was improved. We carried out the cluster analysis to classify the wind sectors using the K-means clustering. South Korea was classified as 8 wind sectors to the annual wind field.

• Journal of Korean Society for Atmospheric Environment
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• v.30 no.6
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• pp.600-618
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• 2014

The metadata for urban meteorological observation is standardized through comparison with those established at the World Meteorological Organization and the Korea Meteorological Administration to understand the surrounding environment around the sites exactly and maintain the networks and sites efficiently. It categorizes into metadata for an observational network and observational sites. The latter is again divided into the metadata for station general information, local scale information, micro scale information, and visual information in order to explain urban environment in detail. The metadata also contains the static information such as urban structure, surface cover, metabolism, communication, building density, roof type, moisture/heat sources, and traffic as well as the update information on the environment change, maintenance, replacement, and/or calibration of sensors. The standardized metadata for urban meteorological observation is applied to the Weather Information Service Engine (WISE) integrated meteorological sensor network and sites installed at Incheon area. It will be very useful for site manager as well as researchers in fields of urban meteorology, radiation, surface energy balance, anthropogenic heat, turbulence, heat storage, and boundary layer processes.