• Title/Summary/Keyword: Reflectance

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Shape recovery and extraction the reflection properties of hybrid reflectance surface(II) (혼성 반사면의 반사 특성 추출 및 형상 복구(II))

  • 김태은;최종수
    • Journal of the Korean Institute of Telematics and Electronics S
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    • v.34S no.6
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    • pp.21-29
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    • 1997
  • In this paper, we propose a new approach for recovering 3-D shape and extracting the reflectance properties of surface from intensity images. Photometric stereo method(PSM) is genrally based on the direct illumination. In this paper, the reflectance function is derived by interoduceing the indirect diffuse illumination in PSM and then applied to hybrid reflectance model which consists of two components; the lambertian and the specular reflectance. Under the hybrid reflectance model and the indirect diffuse illumination circumstance, the reflectance properties of sample surface can be extracting by normal sampler and then 3-D shape of an object can be recovered based on extracting reflectance properties. This method is rapid because of using the reference table and simplifies the restriction condition about the reflectance function existing in prior studies. Th erecovery efficiency in our method is better than that in prior studies. Also, this method is applied to various types of surfaces by defining general reflectance function.

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Obtaining 3-dimensional shape of hybrid reflectance surfaces using indirect diffuse illumination (간접 확산 조명을 이용한 혼성반사 표면의 3차원 형상 취득)

  • 김태은;안호근;최종수
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.21 no.2
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    • pp.301-312
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    • 1996
  • A new approach is presented for recovering the 3-D shape from shading image. Photometric Stereo Method (PSM) is generally based on the direct illumination. In this paper, the reflectance function is derived by introduceing the indirect diffuse illumination in PSM and then applied to hybrid reflectance model which consists fo two components; the Lambertian reflectance and the speclar reflectance. Under the hybrid reflectance model and the indirect diffuse illumination circumstances, the 3-D shape of object can be recovered from the suface normal vector extracted from the surface roughness, the surface reflectance ratio, and the intensity value of a pixel. This method is rapid because of using the reference table and simplifies the restriction condition about the reflectance function existing in prior studies. The recovery efficiency in our method is better than that in prior studies. Also, this method is applied to various types of surfaces by defining general reflectance function.

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Reflectance Characteristics of Al-Si based Alloys according to Powder Size and Composition (Al-Si계 합금의 분말 크기 및 조성에 따른 반사율 변화 특성)

  • Choi, Gwang Mook;Chae, Hong Jun
    • Journal of Korean Powder Metallurgy Institute
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    • v.26 no.1
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    • pp.22-27
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    • 2019
  • In this study, the effects of powder size and composition on the reflectance of Al-Si based alloys are presented. First, the reflectance of Al-Si bulk and powder are analyzed to confirm the effect of powder size. Results show that the bulk has a higher reflectance than that of powder because the bulk has lower surface defects. In addition, the larger the particle size, the higher is the reflectance because the interparticle space decreases. Second, the effect of composition on the reflectance by the changing composition of Al-Si-Mg is confirmed. Consequently, the reflectance of the alloy decreases with the addition of Si and Mg because dendrite Si and $Mg_2Si$ are formed, and these have lower reflectance than pure Al. Finally, the reflectance of the alloy is due to the scattering of free electrons, which is closely related to electrical conductivity. Measurements of the electrical conductivity based on the composition of the Al-Si-Mg alloy confirm the same tendency as the reflectance.

A Study of Reflectance Variations of Solar Concentrators (태양열 집광판의 반사율 변화 연구)

  • Lee, Hyun-Jin;Kim, Jong-Kyu;Lee, Sang-Nam;Kang, Yong-Heack;Lee, Seong-Uk;Park, Moon-Hee
    • Journal of the Korean Solar Energy Society
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    • v.30 no.5
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    • pp.107-114
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    • 2010
  • Understanding of reflectance of solar concentrators is important for assessing concentration performance. However inaccurate data about refractive indices of constituent materials and dust accumulation on the surface often prevent figuring out reflectance variations. The current study proposes an approach calculating concentrator reflectance based on the refractive index of glass obtained from reflectance and transmittance measurements. This approach improved accuracy of solar-averaged reflectance from 2.9% to 0.4% compared to the use of existing reference data. Reflectance variations with incidence angles are negligible up to $60^{\circ}C$ at various glass thicknesses. When concentrators are contaminated with dust during 2 months specular reflectance loss of vertically exposed concentrators is less than 7%. However for horizontally exposed concentrators the loss significantly increases up to 40% while dependence of reflectance on incidence angles becomes strong. Measurements of hemispherical reflectance indicate that 80 percentage of the loss comes from scattering rather than absorption by dust. Data of refractive index and reflectance provided in the current study will help estimate or model the concentrated solar flux.

Spectral Reflectance of Mongsanpo Tidal Flat, Korea, by using Spectroradiometer Experiments and Landsat Data

  • Kim, Bum-Jun;Lee, Sungsoon;Lee, Hoonyol
    • Korean Journal of Remote Sensing
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    • v.33 no.4
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    • pp.411-422
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    • 2017
  • This research aims to analyze spectral reflectance of intertidal zone and its changes under various environmental conditions. We sampled sand of Mongsanpo tidal flat, Korea, and measured its spectral reflectance by using a spectroradiometer under various water contents, compositions and granularity. We also simulated the reflectance of Landsat 7 ETM+ and compared it with an actual satellite data. Five locations were selected for sampling from the coastline towards the ocean. Grain size diminished stepwise from the coastline to ocean direction, while spectral reflectance differed with wavelength. Water contents lowered the overall reflectance especially at the water absorption bands. Spectral reflectance data were then converted into the simulated one by using Landsat 7 ETM+ spectral reflectance function to be compared with the actual Landsat 7 ETM+ images. It showed the decrease of the spectral reflectance due to the increase of moisture contents from seashore towards the ocean. It is shown that Landsat 7 ETM+ imagery can be efficient to extract moisture contents in the tidal flat while compositional analysis needs satellite sensors with much higher spectral resolution.

Apple Quality Measurement Using Hyperspectral Reflectance and Fluorescence Scattering (하이퍼 스펙트랄 반사광 및 형광 산란을 이용한 사과 품질 측정)

  • Noh, Hyun-Kwon;Lu, Renfu
    • Journal of Biosystems Engineering
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    • v.34 no.1
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    • pp.37-43
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    • 2009
  • Hyperspectral reflectance and fluorescence scattering have been researched recently for measuring fruit post-harvest quality and condition. And they are promising for nondestructive detection of fruit quality. The objective of this research was to develop a model, which measure the quality of apple by using hyperspectral reflectance and fluorescence. A violet laser (408 nm) and a quartz tungsten halogen light were used as light sources for generating laser induced fluorescence and reflectance scattering in apples, respectively. The laser induced fluorescence and reflectance of 'Golden Delicious' apples were measured by using a hyperspectral imaging system. Fruit firmness, soluble solids and acid content were measured using standard destructive methods. Principal component analyses were performed to extract critical information from both hyperspectral reflectance and fluorescence data and this information was then related to fruit quality indexes. The fluorescence models had poorer predictions of the three quality indexes than the reflectance models. However, the prediction models of integrating fluorescence and reflectance performed consistently better than the individual models of either reflectance or fluorescence. The correlation coefficient for fruit firmness, soluble solid content, and tillable acidity from the integrated model was 0.86, 0.75, and 0.66 respectively. Also the standard errors were 6.97 N, 1.05%, and 0.07% respectively.

Efficient Method for Recovering Spectral Reflectance Using Spectrum Characteristic Matrix (스펙트럼 특성행렬을 이용한 효율적인 반사 스펙트럼 복원 방법)

  • Sim, Kyudong;Park, Jong-Il
    • Journal of Korea Multimedia Society
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    • v.18 no.12
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    • pp.1439-1444
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    • 2015
  • Measuring spectral reflectance can be regarded as obtaining inherent color parameters, and spectral reflectance has been used in image processing. Model-based spectrum recovering, one of the method for obtaining spectral reflectance, uses ordinary camera with multiple illuminations. Conventional model-based methods allow to recover spectral reflectance efficiently by using only a few parameters, however it requires some parameters such as power spectrum of illuminations and spectrum sensitivity of camera. In this paper, we propose an enhanced model-based spectrum recovering method without pre-measured parameters: power spectrum of illuminations and spectrum sensitivity of camera. Instead of measuring each parameters, spectral reflectance can be efficiently recovered by estimating and using the spectrum characteristic matrix which contains spectrum parameters: basis function, power spectrum of illumination, and spectrum sensitivity of camera. The spectrum characteristic matrix can be easily estimated using captured images from scenes with color checker under multiple illuminations. Additionally, we suggest fast recovering method preserving positive constraint of spectrum by nonnegative basis function of spectral reflectance. Results of our method showed accurately reconstructed spectral reflectance and fast constrained estimation with unmeasured camera and illumination. As our method could be conducted conveniently, measuring spectral reflectance is expected to be widely used.

ESTIMATION OF PHOTOSYNTHETIC LIGHT USE EFFICIENCY IN A SINGLE LEAF BY ANALYZING NARROW-BAND SPECTRAL REFLECTANCE

  • Suh, Kyehong
    • Journal of Photoscience
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    • v.7 no.4
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    • pp.139-142
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    • 2000
  • To examine applicability of some optical indices from reflectance to estimate photosynthetic light use efficiency, photosynthesis, and narrow band spectral reflectance were simultaneously measured at various intensities of light with mongolian oak leaves. Narrow band of the broad-band NDVI was better than photochemical reflectance index and simple ratio to estimate photosynthetic light use efficiency in this study. Changes in spectral reflectance were detected at several wavelengths (540nm, 690nm, 740nm, and 800nm) associated with physiological status of plant leaves that could be components for new optical indices.

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Operational Atmospheric Correction Method over Land Surfaces for GOCI Images

  • Lee, Hwa-Seon;Lee, Kyu-Sung
    • Korean Journal of Remote Sensing
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    • v.34 no.1
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    • pp.127-139
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    • 2018
  • The GOCI atmospheric correction overland surfaces is essential for the time-series analysis of terrestrial environments with the very high temporal resolution. We develop an operational GOCI atmospheric correction method over land surfaces, which is rather different from the one developed for ocean surface. The GOCI atmospheric correction method basically reduces gases absorption and Rayleigh and aerosol scatterings and to derive surface reflectance from at-sensor radiance. We use the 6S radiative transfer model that requires several input parameters to calculate surface reflectance. In the sensitivity analysis, aerosol optical thickness was the most influential element among other input parameters including atmospheric model, terrain elevation, and aerosol type. To account for the highly variable nature of aerosol within the GOCI target area in northeast Asia, we generate the spatio-temporal aerosol maps using AERONET data for the aerosol correction. For a fast processing, the GOCI atmospheric correction method uses the pre-calculated look up table that directly converts at-sensor radiance to surface reflectance. The atmospheric correction method was validated by comparing with in-situ spectral measurements and MODIS reflectance products. The GOCI surface reflectance showed very similar magnitude and temporal patterns with the in-situ measurements and the MODIS reflectance. The GOCI surface reflectance was slightly higher than the in-situ measurement and MODIS reflectance by 0.01 to 0.06, which might be due to the different viewing angles. Anisotropic effect in the GOCI hourly reflectance needs to be further normalized during the following cloud-free compositing.

Surface Morphology and Reflectance of Calcite Filler in Glass Composites (Calcite 필러를 함유한 유리 복합체의 표면형상과 반사율)

  • Jeon, Jae-Seung;Hwang, Seong-Jin;Ahn, Ji-Hwan;Kim, Hyung-Sun
    • Korean Journal of Materials Research
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    • v.19 no.8
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    • pp.407-411
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    • 2009
  • Reflection properties, such as specular reflection and diffuse reflection, are very important optical properties for the reflector, which has high reflectance in the display and architecture industry. Calcite is lowcost, nontoxic, and stable over a wide temperature range. Therefore, it is one of the most widely using fillers in many industries and has some advantages over titania as a filler to improve reflectance. However, optical properties, especially those of ceramic-filled composites, have not been analyzed. We studied the reflectance of calcite composites with their surface roughness. The reflectance of the composites was determined using a UV-visible spectrometer. The surface morphology and the micro-structure of the composites were investigated by atomic force microscope. The reflectance of the composites was improved by increasing the content of calcite in the calcite-frit composite. The reflectance is related with the surface roughness in the composites. However, the reflectance depends on the calcite contents in materials with similar surface roughness.