• 한국태양에너지학회 논문집
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• 제29권2호
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• pp.39-46
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• 2009

Heliostat, as a mirror system tracking the sun's movement, is the most important subsystem determining the efficiency of solar thermal power plant. Thus the accurate sun tracking performance under the various hazardous operating condition, is required. This study presents a methodology of development of the solar ray tracing technique and the application of it in the analysis of sun tracking error due to the heliostat geometrical errors. The geometrical errors considered here are the azimuth axis tilting error and the elevation axis tilting error. We first analyze the geometry of solar ray reflected from the heliostat. Then the point on the receiver, where the solar ray reflected from the heliostat is landed, is computed and compared with the original intended point, which represents the sun tracking error. The result obtained shows that the effect of geometrical error on the sun tracking performance is varying with time(season) and the heliostat location. It also shows that the heliostat located near the solar tower has larger sun tracking error than that of the heliostat located farther.

• Journal of Astronomy and Space Sciences
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• 제24권1호
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• pp.69-78
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• 2007

Earth-Sun-Heliosphere Interactions Experiments(EARTHSHINE) 미션의 주 탑재체인 Albedo Monitor and Radiometer(Amon-Ra) 광학계는 최초로 제1 라그랑제 지점(Lagrange point 1) 주위의 혜일로(Halo) 궤도에 위치하여 태양 복사 활동 및 지구 반사율 변화를 1% 정확도 이내로 측정함으로서 현존하는 지구 반사율 추이의 모순을 해결할 수 있는 과학적 측정 자료를 제시하는데 그 목적을 가지고 있다. 이에 이미 개발된 광학 성능 검증용 Amon-Ra 광학계의 가시광채널 시험 모델 및 광선 추적 기법을 이용한 통합적 광선 추적 end-to-end 과학 임무 성능 평가 수치 모사 기법을 확립하였으며, 개발된 기법을 이용하여 실제 제작된 Amon-Ra 광학계를 제1라그랑제 지점에 위치시키고 태양과 지구 밝기를 다양하게 변화시킨 후 광학계에 입사되는 에너지 복사량을 수치 모사로 측정하였다. 관측된 지구 및 태양 밝기로부터 지구 반사율 변환을 위하여 각 분포 모델(GLobal Angular Distribution Model, ADM)을 이용하였으며 수치 모사에 의한 지구 반사율 측정 결과를 Amon-Ra 광학계의 측정 오차 범위인 ${\pm}0.28%$와 비교함으로서 개발된 end-to-end 성능 검증 기법의 계산 정밀도를 확인하였다. 이는 기존의 광학계 성능 검증법의 한계를 뛰어넘어 광학계 성능 평가를 실시간으로 검증할 수 있다는 점에서 큰 의의를 지닌다.

• 한국태양에너지학회 논문집
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• 제31권2호
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• pp.53-62
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• 2011

Heliostat in the tower type solar thermal power plant is a sun tracking mirror system to reflect the solar energy to the receiver and the optical performance of it affects to the efficiency of whole power plant most significantly. Thus a proper design of structure of the heliostat reflective surface could be the most important step in the construction of such power plant. The work presented here is a design of structure of optical surface of heliostat, which will be used in 200kW solar thermal power plant. The receiver located at 43(m) high from ground in tower has $2{\times}2$(m) rectangular shape. We first developed the software tool to simulate the energy concentration characteristics of heliostat using the ray tracing technique. Then, the shape of heliostat reflective surface is designed with the consideration of heliostat's energy concentration characteristics, production cost and productivity. The designed heliostat's reflective surface has a structure formed by canting four of $1{\times}1$(m) rectangular flat plate mirror facet and the center of each mirror facet is located on the spherical surface, where the spherical surface is formulated by the mirror facet mounting frame.

• 한국태양에너지학회 논문집
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• 제29권3호
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• pp.1-11
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• 2009

Heliostat sun tracking accuracy could be the most important requirement in solar thermal power plant, since it determines the overall efficiency of power plant. This study presents the effect of geometrical errors on the heliostat sun tracking performance. The geometrical errors considered here are the mirror canting error, encoder reference error, heliostat position error. pivot offset and tilt error, gear backlash and mass unbalanced effect error. We first investigate the effect of each individual geometrical error on the sun tracking accuracy. Then, the sun tracking error caused by the combination of individual geometrical error is computed and analyzed. The results obtained using the solar ray tracing technique shows that the sun tracking error due to the geometrical error is varying almost randomly. It also shows that the mirror canting error is the most significant error source, while the encoder reference error and gear backlash are second and the third dominant source of errors.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.28.4-29
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• 2009

The 'Amon-Ra' instrument of the proposed 'EARTHSHINE' satellite is a dual (i.e. imaging and energy) channel instrument for monitoring the total solar irradiance (TSI) and the Earth's irradiance at around the L1 halo orbit. Earlier studies for this instrument include, but not limited to, design and construction of breadboard Amon-Ra imaging channel, stray light suppression and system performance computation using Integrated Ray Tracing (IRT) technique. The Amon-Ra instrument is required to produce 0.3% in uncertainty for both Sunlight and Earthlight measurement. In this study, we report accurate estimation of the output electric signal derived from the orbital variation of radiant exitance from the Sun and the Earth arriving at the aperture and detector plane of the Amon-Ra. For this, orbital irradiance are computed analytically first and then confirmed by simulation using Integrated Ray Tracing (IRT) model. Specially, the results show the arriving power at the bolometer detector surface is $1.24{\mu}W$ for the Sunlight and $1.28{\mu}W$ for the Earthlight, producing the output signal pulses of 34.31 mV and 35.47 mV respectively. These results demonstrate successfully that the arriving radiative power is well within the bolometer detector dynamic range and, therefore, the proposed detector can be used for the in-orbit measurement sequence. We discuss the computational details and implications as well as the simulation results.

• 천문학회보
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• 제37권2호
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• pp.211.1-211.1
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• 2012

The on-orbit test simulation for predicting the instrument directional responsivity was conducted by the Monte Carlo based integrated ray tracing (IRT) computation technique and analytic flux-to-signal conversion algorithms. For the on-orbit test simulation, the Sun model consists of the Lambertian scattering sphere and emitting spheroid rays, the Amon-Ra instrument is a two-channel including a broadband scanning radiometer (energy channel) and an imager with ${\pm}2^{\circ}$ FOV (visible channel). The solar radiation produced by the Sun model is directed to the instrument viewing port and traced through the dual channel optical train. The instrument model is rotated on its rotation axis and this gives a slow scan of the Sun model over the full field of view. The direction of the incident lights are fed with scanned images obtained from the visible channel instrument. The instrument responsivity was computed by the ratio of the incident radiation input to the instrument output. In the radiometric simulation, especially, measured BRDF of the 3D CPC was used for scattering effects on radiometry. With diamond turned 3D CPC inner surface, the anisotropic surface scattering model from the measured data was applied to ray tracing computation. The technical details of the on-orbit test simulation are presented together with field-of-view calibration plan.

• 설비공학논문집
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• 제15권6호
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• pp.533-542
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• 2003

This study aims to propose a simplified mathematical model for calculating vertical air temperature distribution in a four-sided atrium. In the first stage of the mathematical modeling, the computer model combined zonal model and solar radiation model using Monte Carlo method and Ray tracing technique went through a computer simulation with architectural variables applied to a four-sided atrium in summer. In the next stage, Curve Expert, a computer program that gets the most suitable solution ac-cording to the least squares method, is used to analyze the results of the computer simulation and to derive the mathematical model. The accuracy of the mathematical model was evaluated through a comparison of calculation results from a mathematical model and computer simulation. In this validation step using the least square method, the R2 value of the Zones 1, 2 and 3 showed higher than 0.945. Zone 4 has an R2 value of 0.911, lower than the previous three zones. However the relative error was below 0.5%, which is considered very small.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.49.3-49.3
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• 2009

Geostationary Ocean Colour Imager (GOCI) is the first ocean color instrument that will be operating in a geostationary orbit from 2010. GOCI will provide the crucial information of ocean environment around the Korean peninsula in high spatial and temporal resolutions at eight visible bands. We report an on-going development of imaging and radiometric performance prediction model for GOCI with realistic data for reflectance, transmittance, absorption, wave-front error and scattering properties for its optical elements. For performance simulation, Monte Carlo based ray tracing technique was used along the optical path starting from the Sun to the final detector plane for a fixed solar zenith angle. This was then followed by simulation of red-tide evolution detection and their radiance estimation, following the in-orbit operational sequence. The simulation results proves the GOCI flight model is capable of detecting both image and radiance originated from the key ocean phenomena including red tide. The model details and computational process are discussed with implications to other earth observation instruments.