Bidirectional Reflectance Distribution Research Articles

Optical measurement standards for reflective e‐paper to predict colors displayed in ambient illumination environments

AbstractColor displays are viewed in ambient conditions ranging from indoor lighting to bright sunlight. For emissive displays such as phones or tablets, color and readability are disturbed by ambient light reflected from the screen. However, ambient light is required to view e‐paper, so color measurements must be reflection‐based. This article describes how a bidirectional reflectance distribution function‐based methodology for measuring the disturbing reflection on emissive displays has been applied to measure the useful reflection from e‐paper displays. These measurements have been embedded in recently developed optical measurement standards for e‐paper that contain color measurement specifications for spectral reflection and—if a front light is present—spectral radiance of each displayed color. Then the measurements are combined with ambient illumination models to predict how display colors would appear in realistic lighting conditions. Although developed for e‐paper, this concept can be applied to any type of color display. Examples illustrate the standard measurement methodology, and how to predict displayed colors on both handheld e‐paper and emissive displays in both indoor and daylight viewing conditions.

Retrieval of background surface reflectance with pre-running BRD components

Importance of remote sensing for surface is increased than past. So many countries try to many ways to retrieve surface reflectance. In this study, we study a Bidirectional Reflectance Distribution Function (BRDF) to retrieve surface reflectance. We apply BRDF using observed surface reflectance of SPOT/VEGETATION (VGT-S1) and angular data to get Bidirectional Reflectance Distribution (BRD) coefficients for calculating scattering. And then we apply BRDF in the opposite direction with BRD coefficients and angular data to retrieve Background Surface Reflectance (BSR). The range of BSR is not over (blue), (red), (NIR). And for validation we compare BSR with VGT-S1, there are bias is from 0.0116 to 0.0158 and RMSE is from 0.0459 to 0.0545. As a result, we confirm that BSR is similar to VGT-S1.

Bidirectional reflectance of sandy land surface with different particle sizes

The area of sandy land is extending in China because the natural environment suffers the destruction by the human activity. The estimation of the properties and area of sandy land is an important indicative information for improving the environment. Remote sensing technique can provide scientific and effective data sources using its unique advantage. In this study, we measure the bidirectional reflectance information from sandy land surfaces with different particle sizes and analyze the effect of particle size on the reflection characteristics. Then, a comparison is performed between the measured reflectance and the reflectance of sandy land surface with different particle sizes which is computed based on existing model. The results show that the effect of particle size on the bidirectional reflectance distribution is apparent We also find that the bidirectional reflectance of sandy land surface with different particle sizes can be computed using the bidirectional reflectance model when the difference between measured reflection information and modeled reflection information is small. This study not only defines the effect of particle size on the reflectance from sandy land surface, but also provides valuable reference for estimating the particle size from sandy land surface using remote sensing technique and studying the intrinsic optical property of land surface.

Comparison of Two Semi-Empirical BRDF algorithms using SPOT/VGT

The Bidirectional Reflectance Distribution (BRD) effect is critical to interpret the surface information using remotely sensed data. This effect was caused by geometric relationship between sensor, target and solar that is inevitable effect for data of optical sensor. To remove the BRD effect, semi-empirical BRDF models are widely used. It is faster to calculate than physical models and demanded less observation than empirical models. In this study, Ross-Li kernel and Roujean kernel were used respectively in National Aeronautics and Space Administration (NASA) and European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) that are used to compare each other. The semi-empirical model consists of three parts which are isotropic, geometric and volumetric scattering. Each part contained physical kernel and empirical coefficients that were calculated by statistical method. Red and NIR channel of SPOT/VEGETATION product were used to compute Nadir BRDF Adjusted Reflectance (NBAR) over East Asia area from January 2009 to December 2009. S1 product was provided by VITO that was conducted atmospheric correction using Simplified Method of Atmospheric Correction (SMAC). NBAR was calculated using corrected reflectance of red and NIR. Previous study has revealed that Roujean geometric kernel had unphysical values in large zenith angles. We extracted empirical coefficients in three parts and normalized reflectance to compare both BRDF models. Two points located forest in Korea peninsular and bare land in Gobi desert were selected for comparison. As results of time series analysis, both models showed similar reflectance change pattern and reasonable values. Whereas in case of empirical coefficients comparison, different changes pattern of values were showed in isotropic coefficients.

Mapping Savanna Tree Species at Ecosystem Scales Using Support Vector Machine Classification and BRDF Correction on Airborne Hyperspectral and LiDAR Data

Mapping the spatial distribution of plant species in savannas provides insight into the roles of competition, fire, herbivory, soils and climate in maintaining the biodiversity of these ecosystems. This study focuses on the challenges facing large-scale species mapping using a fusion of Light Detection and Ranging (LiDAR) and hyperspectral imagery. Here we build upon previous work on airborne species detection by using a two-stage support vector machine (SVM) classifier to first predict species from hyperspectral data at the pixel scale. Tree crowns are segmented from the lidar imagery such that crown-level information, such as maximum tree height, can then be combined with the pixel-level species probabilities to predict the species of each tree. An overall prediction accuracy of 76% was achieved for 15 species. We also show that bidirectional reflectance distribution (BRDF) effects caused by anisotropic scattering properties of savanna vegetation can result in flight line artifacts evident in species probability maps, yet these can be largely mitigated by applying a semi-empirical BRDF model to the hyperspectral data. We find that confronting these three challenges—reflectance anisotropy, integration of pixel- and crown-level data, and crown delineation over large areas—enables species mapping at ecosystem scales for monitoring biodiversity and ecosystem function.

Radiometric and spectral characterization and comparison of the Antarctic Dome C and Sonoran Desert sites for the calibration and validation of visible and near-infrared radiometers

Global climate change studies require long-term, radiometrically accurate, and stable observations from a number of satellites. Spatially uniform and radiometrically/spectrally stable vicarious calibration sites can be used to quantify the sensor gain change over time, monitor the instrument performance, and compare measurements from multiple instruments to maintain consistent radiometric calibration. This study uses AQUA moderate resolution imaging spectroradiometer (MODIS), MetOp-A advanced very high resolution radiometer (AVHRR), and Earth Observing-1 Hyperion to analyze the radiometric and spectral characteristics of the Dome C and Sonoran Desert sites and perform intercomparisons. The radiometric stability of both sites over a period of eight years as evaluated using AQUA MODIS is found to be better than 2% in the visible (0.64 μm) and near-infrared regions (0.86 μm), assuming the MODIS calibration is stable. The bidirectional reflectance distribution (BRDF) effect over Dome C is large, with greater than 5% seasonal variation, compared to the Sonoran Desert with less than 2% variation. However, the BRDF impact can be reduced to less than 2% for Dome C after normalization by an appropriate BRDF model. For water vapor absorption channels, such as AVHRR channel 2 (0.86 μm), this study suggests that the Sonoran Desert is largely affected with greater than 6% absorption variability compared to that of Dome C with less than 2%. The study also reveals that the operationally calibrated AVHRR top-of-atmosphere reflectance is lower than that of MODIS by about 8%.

Angle‐resolved light scattering from textured injection‐molded plastics

AbstractWith regard to surface appearance, the angle‐resolved light scattering from textured polymeric surfaces was evaluated to link the reflectance properties to measured gloss as well as visually perceived gloss. Bidirectional reflectance distributions were determined by means of a scatterometer and the specimens involved were textured injection‐molded plaques manufactured from three different polymers; an acrylonitrile‐butadiene‐styrene (ABS) copolymer, a polypropylene (PP), and a polycarbonate and ABS copolymer blend (PC/ABS). The influence of color, surface roughness, and angle of incidence on the scattering characteristics was evaluated. An off‐specular reflectance peak was observed for the textured specimens the magnitude of which was clearly determined by the surface roughness and the angle of incidence. The color of the specimens mainly influenced the diffuse reflectance. The results provide a measure of perceived gloss and supported previously reported findings regarding the relevance of the concept of contrast gloss for the gloss characterization of textured polymeric surfaces. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Acquisition and analysis of bispectral bidirectional reflectance and reradiation distribution functions

In fluorescent materials, light from a certain band of incident wavelengths is reradiated at longer wavelengths, i.e., with a reduced per-photon energy. While fluorescent materials are common in ev...

Retrieval of Pinatubo aerosol optical depth and surface bidirectional reflectance from six years of AVHRR global vegetation index data over boreal forests

Six years (1989–1994) of weekly composite satellite data are analyzed with the objective of retrieving the aerosol optical depth over boreal forests. The average surface bidirectional reflectance distribution (BRD) was estimated from a sample of the original data, yielding similar results in different regions around the world. Four analytical models are compared in their ability to reproduce the surface BRD. In channel 1 (0.58–0.68 μm) the surface reflectance averages 0.05 and exceeds 0.10 in the backscattering region. Thus the non‐Lambertian ground contribution could not be neglected in the aerosol retrievals. A relevant radiative transfer code was run in iterative mode to retrieve the aerosol optical depth which best accounts for the difference between modeled surface BRD and measured satellite reflectance in all conditions. From comparisons with Sun photometer data we conclude that a large‐scale, persistent aerosol enhancement such as that resulting from Mount Pinatubo's eruption in 1991 is clearly discernible from weekly composite AVHRR data over boreal forests.

A four-scale bidirectional reflectance model based on canopy architecture

Open boreal forests present a challenge in understanding remote sensing signals acquired with various solar and view geometries. Much research is needed to improve our ability to model the bidirectional reflectance distribution (BRD) for retrieving the surface information using measurements at a few angles. The geometric-optical bidirectional reflectance model presented in this paper considers four scales of canopy architecture: tree groups, tree crowns, branches and shoots. It differs from the Li-Strahler's model in the following respects: 1) the assumption of random spatial distribution of trees is replated by the Neyman distribution which is able to model the patchiness or clumpiness of a forest stand; 2) the multiple mutual shadowing effect between tree crowns is considered using a negative binomial and the Neyman distribution theory; 3) the effect of the sunlit background is modeled using a canopy gap size distribution function that affects the magnitude and width of the hotspot; 4) the branch architecture affecting the directional reflectance is simulated using a simple angular radiation penetration function; and 5) the tree crown surface is treated as a complex surface with microscale structures which themselves generate mutual shadows and a hotspot. All these scales of canopy architecture are shown to have effects on the directional distribution of the reflected radiance from conifer forests. The model results compare well with a data set from a boreal spruce forest.

Changes in Perceived Object Shape with Changes in Lighting Model and Surface Properties

We examined the influence of lighting and bidirectional surface reflectance distribution function (BRDF) on the perceived shape of real objects viewed monocularly and binocularly. We asked observers to adjust a ‘circle-stick’ gradient probe optically superimposed on a smooth, asymmetric, pear-shaped wooden object placed directly in front of the observer at a distance of 60 cm. By using real objects, we avoid problems with unrealistic rendering algorithms and CRT presentation of stimuli. The lighting models used were simple (a single near-punctate source and a flat black background), the viewing conditions (in the binocular case) realistic, and the BDRFs selected not implausible. We did not assume that the viewer's perception of shape is veridical under any of the conditions considered, nor did we assume that surface shape estimated from gradient probe settings is an unbiased estimate of perceived shape. We sought to establish whether changes in lighting model and BRDF affect observer performance and, by implication, perceived shape. Observers viewed the object under all eight of the possible combinations of the binary factors: (a) monocular and binocular viewing of the object, (b) near-punctate illumination from above-left or above-right, and (c) matte wooden BRDF (the natural surface of the object) and gloss white BRDF (the same object painted). For each condition there was a total of ten gradient settings at each of over one hundred surface locations. The same locations were used for each of the eight conditions. We report results of analyses and discuss their implications.

Effects of land cover type and greenness on advanced very high resolution radiometer bidirectional reflectances: Analysis and removal

The objectives of the study are (1) to examine the effects of land cover type, green biomass, and solar zenith angle (SZA) on the bidirectional reflectance distributions (BRDs) of the visible and near‐infrared advanced very high resolution radiometer (AVHRR) data from NOAA 11 over terrestrial surfaces; and (2) to correct for these effects by developing BRD functions (BRDF). Four land cover types are examined: barren, grassland, forest, and cropland. The data used consist of 1‐km daily AVHRR measurements for three growing seasons collected over 19 homogeneous land sites (20×20 km2 for each site) in the conterminous United States and parts of Canada. BRD is found to be strongly land cover dependent. For the same cover type, BRD is altered significantly by the green biomass present (represented by the normalized difference vegetation index (NDVI)). The effects of SZA on BRDs are also observed over all surface types under investigation. Semiempirical BRDFs were developed to account for these effects that are the functions of the SZA, satellite viewing zenith angle, relative azimuth angle, and NDVI. Good agreements were found between the observed and the modeled bidirectional dependencies for wide ranges of NDVI and SZA. A single BRDF appears to be sufficient for bidirectional correction of the clear‐sky AVHRR measurements made over a specific land cover type throughout a season. Finally, the developed BRDFs were used to normalize AVHRR reflectance data to a common geometry and to infer the hemispherical albedos for monitoring the seasonal variations of land surfaces.

AVHRR bidirectional reflectance effects and compositing

The purpose of this study was to assess the magnitude of bidirectional reflectance distribution (BRD) effects in AVHRR Channels 1 and 2 over land, their dependence on land cover, and the possibility of correcting for these effects as part of the AVHRR compositing process. The study was carried out in central Canada using cloud free full (1 km) resolution AVHRR images over 20 days near the peak green period in 1988. All images were coregistered and resampled. Uniform sample sites representing cropland, deciduous and coniferous forest, and wetlands were chosen using Landsat images. The effect of atmospheric corrections and the performance of three vegetation indices were also assessed. The results showed that BRD effects in the AVHRR data depend on land cover type, spectral band, the viewing geometry, and the degree of atmospheric correction. Atmospheric corrections increased the value of NDVI but reduced its variation with satellite zenith angle. BRD dependence in AVHRR Channels 1 and 2 could be modeled quite accurately, but spectral band- and land cover-specific model parameters were required for a good fit with the measurements. It is concluded that in AVHRR compositing based on the maximum NDVI value, the most-cloud-free pixel selection should precede atmospheric corrections and the correction for BRD effects. BRD correction models should be derived using data with similar spectral and spatial characteristics, preferably from the same sensor.

Computer controlled facility for measurement of the bidirectional scattering distribution function

A computer controlled facility for measurement of the bidirectional scattering distribution function is described, with application to the evaluation of spacecraft surface contamination in optical and thermal control systems. An automatic detector/sampleholder allows a 360-deg detector scan around the sample for a complete bidirectional reflectance and transmittance distribution function characterization. The system demonstrates reduced data acquisition and reduction cycle time, and improved accuracy.