• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.178-181
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• 2005

The positioning accuracy of the Global Positioning System (GPS) has been improved considerably during the past two decades. The main error sources such as ionospheric refraction, orbital uncertainty, antenna phase center variation, signal multipath, and tropospheric delay have been reduced substantially, if not eliminated. In this study, the GPS data collected by the GPS receivers that were established as continuously operating reference stations by International GNSS Service (IGS), Ministry of the Interior (MOl), Central Weather Bureau (CWB), and Industrial Technology Research Institute (ITRI) Of Taiwan are utilized to investigate the impact of atmospheric water vapor on GPS positioning determination. The surface meteorological measurements that were concurrently acquired by instruments co-located with the GPS receivers include temperature, pressure and humidity data. To obtain the influence of the GPS height on the proposed impact study. A hydrodynamic ocean tide model (GOTOO.2 model) and solid earth tide were used to improve the GPS height. The surface meteorological data (pressure, temperature and humidity) were introduced to the data processing with 24 troposphere parameters. The results from the studies associated with different GPS height were compared for the cases with and without a priori knowledge of surface meteorological measurements. The finding based on the measurements in 2003 is that the surface meteorological measurements have an impact on the GPS height. The associated daily maximum of the differences is 1.07 cm for the KDNM station. The impact is reduced due to smoothing when the average of the GPS height for the whole year is considered.

• Journal of Astronomy and Space Sciences
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• v.10 no.2
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• pp.189-196
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• 1993

Satellite laser ranging observation of LAGEOS II has been performed using the SLR System at Sheshan Laser Ranging Station, Shanghai Observatory. And we obtained 1,838 observational points. The observed range data is corrected by means of system delay correction using ground target observation, atmospheric refraction delay correction, offset correction, general relativistic correction and tide correction including solid tide, polar tide and ocean tide. As a result, the determined range delay mean value is 19.12m and the mean internal accuracy by means of polynomial fitting and least square method is $\pm$7cm. Corrected observational points are 1,340 and noise ratio to total observational points is 27.1%.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.76.2-76.2
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• 2012

The understanding spectral characterization of possible earth-like extra solar planets has generated wide interested in astronomy and space science. The technical central issue in observation of exoplanet is deconvolution of the temporally and disk-averaged spectra of the exoplanets. The earth model based on atmospheric radiative transfer method has been studied in recent years for solutions of characterization of earthlike exoplanet. In this study, we report on the current progress of the new method of 3D earth model as a habitable exoplanet. The computational model has 3 components 1) the sun model, 2) an integrated earth BRDF (Bi-directional Reflectance Distribution Function) model (Atmosphere, Land and Ocean) and 3) instrument model combined in ray tracing computation. The ray characteristics such as radiative power and direction are altered as they experience reflection, refraction, transmission, absorption and scattering from encountering with each all of optical surfaces. The Land BRDF characteristics are defined by the semi-empirical "parametric-kernel-method" from POLDER missions from CNES. The ocean BRDF is defined for sea-ice cap structure and for the sea water optical model, considering sun-glint scattering. The input cloud-free atmosphere model consists of 1 layers with vertical profiles of absorption and aerosol scattering combined Rayleigh scattering and its input characteristics using the NEWS product in NASA data and spectral SMARTS from NREL and 6SV from Vermote E. The trial simulation runs result in phase dependent disk-averaged spectra and light-curves of a virtual exoplanet using 3D earth model.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.407-410
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• 2002

Thermal oxidations of 3C-SiC thin-films grown on Si(100) by APCVD(atmospheric pressure chemical vapor deposition) were carried out. The oxidations of 3C-SiC were performed at $1100^{\circ}C$ for 1~6 hr in wet and dry $O_2$ ambient, respectively. Ellipsometry was used to determine the thickness and index of refraction of oxide films. The oxide thickness vs. the oxidation time follows the general relationship used for the thermal oxidation of Si. The surface roughness was analyzed by using AFM(atomic force microscopy). The surface roughness of oxidized 3C-SiC was rougher than before oxidation. The thermal oxide was found to be $SiO_2$ by XPS(X-ray photoelectron spectroscopy) analysis. Auger analysis showed them to be homogeneous with near stoichiometric composition.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.1
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• pp.123-129
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• 2014

This paper presents an altitude detection accuracy for long range and multifunction radar. The accuracy is difficult to estimate because it is affected by an time varying atmosphere refractivity. We analyze altitude accuracy with a raytracing simulator with atmosphere refractivity. An altitude error is simulated with measured and modeled refractivity, and the modeled refractivity is used for compensate an altitude accuracy. As a result, the error is modeled with normal distribution function, and analyzed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.12
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• pp.164-175
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• 2008

Atmospheric effects on laser beam propagation can be broken down into two categories: attenuation of the laser power and fluctuation of laser power due to laser beam deformation. Attenuation consists of scattering of the laser light photons by the fog. Laser beam deformation occurs because of small-scale dynamic changes in the index of refraction of the atmosphere. This causes pointing error. In order to analyse these effect on optical wireless communication system, in this paper uses cassegrain optics as a transmitting and receiving telescope, AID as a detecting device and ill as a light source. The signal modulating and demodulating method is a IM/DD. I show the effects of fog and pointing error and calculate the possible communication distance for BER is $10^{-9}$.

• Publications of The Korean Astronomical Society
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• v.23 no.2
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• pp.53-63
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• 2008

Korea Astronomy and Space Science Institute (KASI), direct decendant of Korea National Astronomy Observatory, has been publishing Korean Astronomical Almanac since in 1976. The almanac contains essential data in our daily lives such as the times of sunrise, sunset, moonrise, and moonset, conversion tables between luni-solar and solar calendars, and so forth. So, we are planning to register Korean astronomical almanac data for national Standard Reference Data(SRD), which is a scientific/technical data whose the reliablity and the accuracy are authorized by scientific analysis and evalution. To be certificated as national SRD, reference data has to satisfy several criteria such as traceability, consistency, uncertainty, and so on. Based on similarity among calculation processes, we classified astronomical almanac data into three groups: Class I, II, and III. We are planning to register them for national SRD in consecutive order. In this study, we analyzed Class I data which is aimed to register in 2009, and presented the results. Firstly, we found that the traceability and the consistency can be ensured by the usage of NASA/JPL DE405 ephemeris and by the comparsion with international data, respectively. To evaluate uncertainty in Class I data, we solved the mathematical model and determined the factors influencing the calculations. As a result, we found that the atmospheric refraction is the main factor and leads to a variation of ${\pm}16$ seconds in the times of sunrise and sunset. We also briefly review the histories of astronomical almanac data and of standard reference data in Korea.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.2
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• pp.188-197
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• 2016

In this paper, we propose a method that represents a mathematical form of wave propagation by using the fact the refractive index determining wave propagation characteristic is a function of altitude. Proposed method uses Snell's law that expresses relationship between incident angle and refraction angle when incident wave passes medium having a different refractive index. We present the simulation results about wave propagation by setting the square of refractive index in the form of the polynomial for altitude and show that it is possible to estimate the coefficients of the polynomial through the angle information from vertical axis of multiple radar systems.

• Korean Journal of Remote Sensing
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• v.37 no.3
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• pp.603-614
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• 2021

Recently, the surface temperature in the seas around Korea has been continuously rising. This temperature rise causes changes in fishery resources and affects leisure activities such as fishing. In particular, high temperatures lead to the occurrence of red tides, causing severe damage to ocean industries such as aquaculture. Meanwhile, changes in sea temperature are closely related to military operation to detect submarines. This is because the degree of diffraction, refraction, or reflection of sound waves used to detect submarines varies depending on the ocean mixed layer. Currently, research on the prediction of changes in sea water temperature is being actively conducted. However, existing research is focused on predicting only the surface temperature of the ocean, so it is difficult to identify fishery resources according to depth and apply them to military operations such as submarine detection. Therefore, in this study, we predicted the temperature of the ocean mixed layer at a depth of 38m by using temperature data for each water depth in the upper mixed layer and meteorological data such as temperature, atmospheric pressure, and sunlight that are related to the surface temperature. The data used are meteorological data and sea temperature data by water depth observed from 2016 to 2020 at the IEODO Ocean Research Station. In order to increase the accuracy and efficiency of prediction, LSTM (Long Short-Term Memory), which is known to be suitable for time series data among deep learning techniques, was used. As a result of the experiment, in the daily prediction, the RMSE (Root Mean Square Error) of the model using temperature, atmospheric pressure, and sunlight data together was 0.473. On the other hand, the RMSE of the model using only the surface temperature was 0.631. These results confirm that the model using meteorological data together shows better performance in predicting the temperature of the upper ocean mixed layer.