• Journal of Astronomy and Space Sciences
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• v.22 no.4
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• pp.537-558
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• 2005

This paper addresses the results of HAUSAT-2 radiation environment and effect analyses, including TID and SEE analyses. Trapped proton and electron, solar proton, galactic cosmic ray models were considered for HAUSAT-2 TID radiation environment analysis. TID was analyzed through total dose-depth curve and the radiation tolerance of TID for HAUSAT-2 components was verified by using DMBP method and sectoring analysis. HAUSAT-2 LET spectrum for heavy ion and proton were also analyzed for SEE investigation. SEE(SEU, SEL) analyses were accomplished for MPC860T2B microprocessor and K6X8008T2B memory. It was estimated that several SEUs may occur without SEL during the HAUSAT-2 mission life(2 years). Software Hamming Code EDAC has been implemented to detect and correct the SEU. In this study, all radiation analyses were conducted by using SPENVIS software.

• Ocean Science Journal
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• v.42 no.2
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• pp.103-116
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• 2007

Seasonal changes of tide signal(s), temperature, salinity and current were studied during the years 2004-2005 in the northernmost Gulf of Aqaba, which is under developmental activities, to obtain scientific bases for best management and sustainability. Spectrum analysis revealed permanent signals of tide measurements during all seasons, which represented semidiurnal and diurnal barotropic tides. The other signal periods of 8.13, 6.10-6.32, 4.16 and 1.02-1.05 h were not detected in all seasons, which were related to shallow water compound and overtides of principle solar and lunar constituent and to seiches generated in the Red Sea and the Gulf of Aqaba. Spatial and temporal distribution of temperature, salinity and density showed significant differences between months in the coastal and offshore region and no significant differences among the coastal sites, between the surface and bottom waters and between coastal and offshore waters. Therefore, the temporal and spatial variation of water properties in the northernmost Gulf of Aqaba behave similarly compared to other parts. The coastal current below 12 m depth was weak $(3-6\;cms^{-1})$ and fluctuated from east-northeastward to west-southwestward (parallel to the shoreline), which may be related to the effect of bottom topography and/or current density due to differential cooling between eastern and western parts in the study area, and wind-induced upwelling and downwelling in the eastern and western side, respectively. The prevailing northerly winds and stratification conditions during summer were the main causes of the southward current at 6 and 12 m depths with average speed of 28 and $12cms^{-1}$ respectively.

• Korean Chemical Engineering Research
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• v.55 no.6
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• pp.731-744
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• 2017

Triplet-triplet annihilation upconversion (TTA-UC) is a special photochemical process that converts low energy photons to higher energy photon via combination of organic chemicals which fulfill specific energetic criteria. TTA-UC has been known as attractive technology that is able to enhance energy conversion efficiency of the photonic devices based on sunlight, which is achieved by conversion of wasted low energy photons in solar spectrum into higher energy photon. In the present paper, we introduced the photochemical mechanism and characteristics of TTA-UC phenomenon, which is yet unfamiliar to the domestic academia, and investigated recent research status, application, and future research directions of TTA-UC technology.

• Transactions of the Korean hydrogen and new energy society
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• v.3 no.2
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• pp.25-33
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• 1992

With the aim to obtain $TiO_2$ films with an increased photorespones and absorbance in the visible region of the solar spectrum, the direct oxidation of titanium alloys were performed. In this study, $Ti-Ga_2O_3$ alloy was prepared by mixing, pressing and arc melting of appropriate amounts of titanium and $Ga_2O_3$ powder. Electrochemical measurements were performed in three electrode cell using electrolyte of 1M NaOH solution. The oxide films on $Ti-Ga_2O_3$ alloy was composed of $Ti_2O$, TiO, $TiO_2$, $Ga_2TiO_5$. The free energy efficiency (${\eta}e$) of $Ti-Ga_2O_3$ oxide films had 0.8~1.3 % and were increased with the increase of $Ga_2O_3$ content up to 10wt %. The onset potential ($V_{on}$) had -0.8V~0.9V ranges and were shifted to anodic direction with the increase of $Ga_2O_3$ content. The spectral response of Ti-$Ga_2O_3$ oxides were similar to the response of the $TiO_2$ and their $E_g$ were observed to 2.90~3.0eV. Variations of onset potential($V_{on}$) associated with electrolyte pH were -59mV/pH. This probably reflects the nature of the bonding of $OH^-$ ion to the $TiO_2$ surface, a common phenomena in the transition-metal oxides.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.122-122
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• 2012

Geosynchronous electron flux dropouts are most likely due to fast drift loss of the particles to the magnetopause (or equivalently, the "magnetopause shadowing effect"). A possible effect related to the drift loss is the radial diffusion of PSD due to gradient of PSD set by the drift loss effect at an outer L region. This possibly implies that the drift loss can affect the flux levels even inside the trapping boundary. We recently investigated the details of such diffusion process by solving the diffusion equation with a set of initial and boundary conditions set by the drift loss. Motivated by the simulation work, we have examined observationally the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropouts. For this work, we have first identified a list of geosynchronous flux dropout events for 2007-2010 from GOES satellite electron measurements and solar wind pressures observed by ACE satellite. We have then used the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements to investigate the particle fluxes. The five THEMIS spacecraft sufficiently cover the inner magnetospheric regions near the equatorial plane and thus provide us with data of much higher spatial resolution. In this paper, we report some case studies showing energy dependence during magnetopause shadowing effect.

• Journal of the Korean institute of surface engineering
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• v.53 no.1
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• pp.9-14
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• 2020

CuS (copper sulfide) thin films having the same thickness of 100nm were deposited on the glass substrates using by radio frequency (RF) magnetron sputtering method. RF powers were applied as a process variable for the growth of CuS thin films. The structural and optical properties of CuS thin films deposited under different power conditions (40-100W) were studied. XRD analysis revealed that all CuS thin films had hexagonal crystal structure with the preferential growth of (110) planes. As the sputtering power increased, the relative intensity of the peak with respect to the (110) planes decreased. The peaks of the two bands (264cm^-1 and 474cm^-1) indicated in the Raman spectrum exactly matched the typical spectral values of the covellite (CuS). The size and shape of the grains constituting the surface of the CuS thin films deposited under the power condition ranging from 40W to 80W hardly changed. However, the spacing between crystal grains tended to increase in proportion to the increase in sputtering power. The maximum transmittance of CuS thin films grown at 40W to 80W ranged from 50 % to 51 % based on 580nm wavelength, and showed a relatively small decrease of 48% at 100W. The band gap energy of the CuS thin films decreased from 2.62eV (at 40W) to 2.56eV (at 100W) as the sputtering power increased.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.1555-1562
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• 2015

Metal oxide semiconductors have been applied in several areas, such as solar cells, sensor, optical elements and displays, due to the high surface area, unique electrical and optical characteristics. Zinc oxide among the metal oxide has excellent physicochemical properties. Zinc oxide is a n-type semiconductor with a wide direct transition band gap of 3.37 eV at room temperature and large exciton binding energy of 60 meV. Cation-doped zinc oxide studies were conducted to complement the electrical and optical characteristics. In this paper, Al-doped ZnO was synthesized by hydrothermal synthesis using microwaves. ZnO was synthesized by adjusting the precursor ratio and using different dopants. The optimal ZnO synthesis conditions for crystal shape and optical properties were determined. The optical properties of aluminum doped zinc oxide were then examined by SEM, XRD, PL, UV-vis absorbance spectrum, and EDS.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.2
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• pp.233-240
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• 2021

For the production of neodymium-doped zinc sulfide thin films in various amounts, zinc sulfide and neodymium were simultaneously deposited using an RF magnetron sputtering equipment to form a thin films, and rapid thermal annealing was performed at 400℃ for 30 minutes as a post-treatment process. The structure, shape, and optical properties of ZnS thin films having various neodymium doping contents (0.35at.%, 1.31at.%, 1.82at.% and 1.90at.%) were studied. The X-ray diffraction pattern was grown to a (111) cubic structure in all thin films. The surface and structural morphology of the thin films due to the neodymium doping content was explained through SEM and AFM images. Only elements of Zn, S, and Nd that do not contain other impurities were identified through EDAX. The transmittance and band gap of the prepared thin films were confirmed using the UV-vis spectrum.

• Korean Journal of Remote Sensing
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• v.37 no.1
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• pp.161-167
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• 2021

This paper presents the method to quantitatively evaluate the uncertainty of the semi-empirical Bidirectional Reflectance Distribution Function (BRDF) model for Himawari-8/AHI. The uncertainty of BRDF modeling was affected by various issues such as assumption of model and number of observations, thus, it is difficult that evaluating the performance of BRDF modeling using simple uncertainty equations. Therefore, in this paper, Monte-Carlo method, which is most dependable method to analyze dynamic complex systems through iterative simulation, was used. The 1,000 input datasets for analyzing the uncertainty of BRDF modeling were generated using the Second Simulation of a Satellite Signal in the Solar Spectrum (6S) Radiative Transfer Model (RTM) simulation with MODerate Resolution Imaging Spectroradiometer (MODIS) BRDF product. Then, we randomly selected data according to the number of observations from 4 to 35 in the input dataset and performed BRDF modeling using them. Finally, the uncertainty was calculated by comparing reproduced surface reflectance through the BRDF model and simulated surface reflectance using 6S RTM and expressed as bias and root-mean-square-error (RMSE). The bias was negative for all observations and channels, but was very small within 0.01. RMSE showed a tendency to decrease as the number of observations increased, and showed a stable value within 0.05 in all channels. In addition, our results show that when the viewing zenith angle is 40° or more, the RMSE tends to increase slightly. This information can be utilized in the uncertainty analysis of subsequently retrieved geophysical variables.

• 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.