• Korean Journal of Remote Sensing
• /
• v.27 no.3
• /
• pp.303-314
• /
• 2011

Surface albedo is an important parameter of the surface energy budget, and its accurate quantification is of major interest to the global climate modeling community. Therefore, in this paper, we consider the direct solution of kernel based bidirectional reflectance distribution function (BRDF) models for retrieval of normalized reflectance of high resolution satellite. The BRD effects can be seen in satellite data having a wide swath such as SPOT/VGT (VEGETATION) have sufficient angular sampling, but high resolution satellites are impossible to obtain sufficient angular sampling over a pixel during short period because of their narrow swath scanning when applying semi-empirical model. This gives a difficulty to run BRDF model inferring the reflectance normalization of high resolution satellites. The principal purpose of the study is to estimate normalized reflectance of high resolution satellite (RapidEye) through BRDF components from SPOT/VGT. We use semi-empirical BRDF model to estimated BRDF components from SPOT/VGT and reflectance normalization of RapidEye. This study used SPOT/VGT satellite data acquired in the S1 (daily) data, and within this study is the multispectral sensor RapidEye. Isotropic value such as the normalized reflectance was closely related to the BRDF parameters and the kernels. Also, we show scatter plot of the SPOT/VGT and RapidEye isotropic value relationship. The linear relationship between the two linear regression analysis is performed by using the parameters of SPOTNGT like as isotropic value, geometric value and volumetric scattering value, and the kernel values of RapidEye like as geometric and volumetric scattering kernel Because BRDF parameters are difficult to directly calculate from high resolution satellites, we use to BRDF parameter of SPOT/VGT. Also, we make a decision of weighting for geometric value, volumetric scattering value and error through regression models. As a result, the weighting through linear regression analysis produced good agreement. For all sites, the SPOT/VGT isotropic and RapidEye isotropic values had the high correlation (RMSE, bias), and generally are very consistent.

• Korean Journal of Computational Design and Engineering
• /
• v.14 no.5
• /
• pp.346-354
• /
• 2009

BRDF (bidirectional reflectance distribution function) is critical in realistic simulation of material appearances since it models the directional characteristics of reflection of light. Although many BRDF models have been proposed so far, it is still not easy to find one specific model that could represent all the reflection properties of real materials such as generalized diffusion, off-specular reflection, Fresnel effect, and back scattering. In this paper, we compare three BRDF models including B-spline volume BRDF (BVB), Cook-Torrance, and Lafortune in their ability to represent the measured BRDF data for physically-based rendering. We show that B-spline volume BRDF surpass the others in quality of data fitting and rendering, especially for materials without specular reflections.

• Korean Journal of Remote Sensing
• /
• v.26 no.6
• /
• pp.653-664
• /
• 2010

The land surface reflectance is a key parameter influencing the climate near the surface. Therefore, it must be determined with sufficient accuracy for climate change research. In particular, the characteristics of the bidirectional reflectance distribution function (BRDF) when using earth observation system (EOS) are important for normalizing the reflected solar radiation from the earth's surface. Also, wide swath satellites like SPOT/VGT (VEGETATION) permit sufficient angular sampling, but high resolution satellites are impossible to obtain sufficient angular sampling over a pixel during short period because of their narrow swath scanning. This gives a difficulty to BRDF model based reflectance normalization of high resolution satellites. The principal objective of the study is to add BRDF modeling of high resolution satellites and to supply insufficient angular sampling through identifying BRDF components from SPOT/VGT. This study is performed as the preliminary data for apply to high-resolution satellite. The study provides surface parameters by eliminating BRD effect when calculated biophysical index of plant by BRDF model. We use semi-empirical BRDF model to identify the BRD components. This study uses SPOT/VGT satellite data acquired in the S1 (daily) data. Modeled reflectance values show a good agreement with measured reflectance values from SPOT satellite. This study analyzes BRD effect components by using the NDVI(Normalized Difference Vegetation Index) and the angle components such as solar zenith angle, satellite zenith angle and relative azimuth angle. Geometric scattering kernel mainly depends on the azimuth angle variation and volumetric scattering kernel is less dependent on the azimuth angle variation. Also, forest from land cover shows the wider distribution of value than cropland, overall tendency is similar. Forest shows relatively larger value of geometric term ($K_1{\cdot}f_1$) than cropland, When performed comparison between cropland and forest. Angle and NDVI value are closely related.

• Journal of Computational Design and Engineering
• /
• v.2 no.1
• /
• pp.1-15
• /
• 2015

Measured bidirectional reflectance distribution function (BRDF) data have been used to represent complex interaction between lights and surface materials for photorealistic rendering. However, their massive size makes it hard to adopt them in practical rendering applications. In this paper, we propose an adaptive method for B-spline volume representation of measured BRDF data. It basically performs approximate B-spline volume lofting, which decomposes the problem into three sub-problems of multiple B-spline curve fitting along u-, v-, and w-parametric directions. Especially, it makes the efficient use of knots in the multiple B-spline curve fitting and thereby accomplishes adaptive knot placement along each parametric direction of a resulting B-spline volume. The proposed method is quite useful to realize efficient data reduction while smoothing out the noises and keeping the overall features of BRDF data well. By applying the B-spline volume models of real materials for rendering, we show that the B-spline volume models are effective in preserving the features of material appearance and are suitable for representing BRDF data.

• 한국HCI학회:학술대회논문집
• /
• 2007.02a
• /
• pp.1019-1024
• /
• 2007

그래픽스 분야에서 다양한 재질을 사실감 있게 표현하려는 연구가 활발히 진행되고 있는 가운데, 다양한 재질의 반사특성을 측정하는 방법들이 시도되고 있다. 본 연구에서는 디지털 카메라를 이용하여 영상 기반 양방향 반사 분포함수(BRDF: Bidirectional Reflectance Distribution Function)를 획득할 수 있는 측정 시스템을 구축하였다, 이를 통한 BRDF 모델은 경험적(empirical)혹은 물리(physical)기반의 모델에 비해 보다 사실성 높은 표현이 가능하다. 영상 기반으로 양방향 반사 분포함수를 생성하는 과정에서 노출시간을 달리한 여러 장의 영상을 가지고 HDR(High Dynamic Range) 영상을 생성하였다. 또한 원색재현을 위해 표준광원을 사용하고 컬러차트와 회귀분석을 통해 컬러 보정을 수행하였다. 본 연구에서는 플라스틱이나 금속재질같이 불투명한 등방성(isotropic) 재질을 사용하였고, 이러한 재질의 BRDF데이터를 통해 산업제품에서 많이 사용되는 재질의 모델을 보다 실감나게 렌더링(rendering)할 수 있다.

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

• 한국HCI학회:학술대회논문집
• /
• 2007.02a
• /
• pp.1037-1044
• /
• 2007

Metallic paint is one of the most widely used coating in automotive, cosmetic and other applications because of its well-known ability to give a product realistic look which creates widespread consumer appeal. But, this coating has complicated subsurface structure which includes pigments, flakes, and transparent clearcoat. Though various analytic reflection models are available to simulate appearance of various surfaces, it is difficult to select an appropriate reflection model with faithful parameters for simulating this coating due to the complex subsurface structure of metallic paints. This paper presents a framework for accurate modeling of metallic coating by determining an appropriate reflection model among various existing BRDF (Bidirectional Reflectance Distribution Function) models. The selection of the appropriate model is achieved by measuring BRDF of various metallic paint samples using a BRDF measuring device i.e. gonioreflectometer and fitting an existing model to the measured data. Then, this model is effectively realized by rendering metallic painted surfaces. We believe that this framework can serve as a guide for those who wants to render metallic painted surfaces accurately with analytic BRDF model without expending time on extracting BRDF data using gonioreflectometer from real metallic paint sample.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.6
• /
• pp.577-585
• /
• 2010

This paper is a part of developing a software that predicts the infrared signal emitted from a ground object by considering solar irradiation. The radiance emitted from a surface can be calculated by using the temperature and optical characteristics of the surface object. The bidirectional reflectance distribution function (BRDF) is defined as the ratio of reflected radiance to incident irradiance. It is a very important surface reflection property that decides the reflected radiance from the object. In this paper, the spectral radiance received by a remote sensor over the mid-wave infrared(MWIR), and the long-wave infrared(LWIR) regions are computed and compared each other for several different materials. The results show that the optical surface properties such as the BRDF and the emissivity of the object surface can play a major role in generating the infrared signatures of various objects, and the largest infrared signal may reach up to 10 times the smallest one when the infrared signals obtained from a flat plate with different surface conditions under the sun light.

• Journal of Welding and Joining
• /
• v.13 no.1
• /
• pp.115-126
• /
• 1995

Vision sensors using the optical triangulation have been widely used for automatic welding systems in various ways, but their reliability is seriously affected by presence of the arc noise. The reliability of vision sensors was analyzed with variation of the arc noise by considering the reflectance of the base metal. first, the properties of the base metal's reflection were modelled by using the Bidirectional Reflectance-Distribution Function(BRDF), and then the variation of the reflected arc intensity was formulated for various configurations of the torch, base metal, and sensor. The experimental data of the gray level of the reflected arc light were obtained for two materials, mild steel and stainless steel. It was found that the results calculated from the proposed model were in good agreement with the experimental data.

• Korean Journal of Remote Sensing
• /
• v.36 no.6_2
• /
• pp.1523-1535
• /
• 2020

In order to produce crop information using remote sensing, we use classification and growth monitoring based on crop phenology. Therefore, time-series satellite images with a short period are required. However, there are limitations to acquiring time-series satellite data, so it is necessary to use fusion with other earth observation satellites. Before fusion of various satellite image data, it is necessary to overcome the inherent difference in radiometric characteristics of satellites. This study performed Korea Multi-Purpose Satellite-3 (KOMPSAT-3) cross calibration with Landsat-8 as the first step for fusion. Top of Atmosphere (TOA) Reflectance was compared by applying Spectral Band Adjustment Factor (SBAF) to each satellite using hyperspectral sensor band aggregation. As a result of cross calibration, KOMPSAT-3 and Landsat-8 satellites showed a difference in reflectance of less than 4% in Blue, Green, and Red bands, and 6% in NIR bands. KOMPSAT-3, without on-board calibrator, idicate lower radiometric stability compared to ladnsat-8. In the future, efforts are needed to produce normalized reflectance data through BRDF (Bidirectional reflectance distribution function) correction and SBAF application for spectral characteristics of agricultural land.