Spectral Reflectance Distribution Research Articles

Evaluating Emerging Spectral Lighting Software: Comparing Measurements of Light Spectrum and Derived Metrics in a One-Room Laboratory Environment with Simulation Results

ABSTRACT The goal of this study was to evaluate the use of new spectral simulation tool, Adaptive Lighting for Alertness (ALFA), by comparing software-predicted values of spectral irradiance, illuminance, and equivalent melanopic lux (EML) to corresponding measurements captured in a laboratory environment with light-emitting diode (LED) luminaires. Four lighting conditions were considered by varying the correlated color temperature (CCT) of the LED luminaires. Meter measurements of space geometry, spectral reflectance distribution (SRDs) of materials, and spectral power distribution of luminaires were used as input to the simulation. Simulated spectral irradiance values between 400 and 700 nm were generally within 10% of measured values, with many spectral bands having less than 5% error. Larger mean absolute percent error (MAPE) was observed for the mixed lighting conditions for bands between 420 and 490 nm, which subsequently influenced calculated EML values. Compared to horizontal measurements, vertical measurements were particularly susceptible to additional error through the measurement procedure and measurement equipment.

Opto-Electrical Properties of Graphene Oxide Liquid Crystal Films

Graphene Oxide Liquid Crystal (GOLC) was prepared using the improved Hummer’s method. A particular purification methodology is used to reduce the disadvantages of the common purification methods. The thin films of GOLC were prepared using a wasteless low-cost drop-casting method. The optical parameters are determined for GOLC films of different thicknesses in the range from 400 nm to 2000 nm. The spectral distribution of transmittance and reflectance of GOLC films was investigated in the wavelength range from 300 nm to 2000 nm. The refractive index of GOLC films was analyzed according to the single oscillator model. The oscillator and dispersion energies are estimated using the Wemple-DiDomenico (WDD) method. The allowed transitions in GOLC films are found to be indirect, with the energy gap decreasing gradually with increasing film thickness in the investigated range. The optical and electrical conductivities as functions of photon energy are explored. Also, the third-order susceptibility and non-linear refractive index are calculated.

Effect of indoor surfaces’ spectral reflectance on the environmental light spectrum modification and on objects perceived color

In indoor lighting, the illuminance and spectral power distribution of the light incident on the contained objects, and hence the color rendering abilities, are not only due to light sources, but also to the indoor architectural surface's geometrical and lighting properties (e.g. spectral reflectance functions). This circumstance, for interior lighting designers, might be as relevant as the appropriate choice of light sources;Main purpose of the study is to highlight how coloured walls can affect indoor environmental light and modify objects perceived color; despite its importance, it is quite a neglected aspect, and has been little investigated, especially in comparison to a wide range of studies about users’ satisfaction with the correlated color temperature of the emitted light and the ability of such artificial light in rendering colors. To take into account spectral reflectance distribution of surfaces, a mathematic calculation model has been developed and implemented in Matlab. This paper evaluates, through numerical simulations, the relative importance of the two factors – light sources and properties of the walls-having influence on indoor lighting.A primary source with CIE D50 spectrum has been considered, and the effect of diffuse Lambertian reflection from the walls with different spectral reflectance functions, to evaluate the spectrum of the light incident on different tasks in the room, and the consequent impact on their color appearance have been studied. Influence of objects’ position has also been investigated. Resultsshow that this impact is remarkable, and are visually presented through a graphic coloured pictorial representation, giving evidence of how perceived colors of objects in an environment with coloured walls appear different from the case of white or grey walls, or of presence of direct light only. This result is highlighted also through the use of a Color rendition index that reaches, in some cases, values far from the optimum.

Preliminary Selection and Characterization of Pseudo-Invariant Calibration Sites in Northwest China

Pseudo-invariant calibration sites (PICS) have been used for the radiometric calibration and stability monitoring of satellite optical sensors. Several stable PICS, such as those in the Sahara Desert in North Africa, were selected for the vicarious calibration of earth remote sensing satellites. However, the selection procedure of PICSs in the whole of Northwest China has not been fully explored before. This paper presents a novel technique for selecting PICS in Northwest China by combined using the coefficient of variation (CV) and the iteratively reweighted multivariate alteration detection (IR-MAD) technique. IR-MAD, which calculates the differences between two multispectral N-band images from the same scene acquired at different times, is used to identify no-change pixels (NCPs) of the scene through one image pair. The NCPs from IR-MAD using the long-term data of FY-3 visible infrared radiometer (VIRR) and aqua Moderate Resolution Imaging Spectroradiometer (MODIS) were aggregated into the contiguously stable sites. The traditional spatial uniformity and temporal stability from MODIS surface products were used to select the potential PICS. By combining the results of both methods, over thirty PICSs with a wider brightness range of the scene types were selected. To confirm and characterize these PICSs over Northwest China, Landsat operational land imager (OLI) high-spatial-resolution images were used to check the spatial uniformity of the selected site to determine the specific location and the size of these sites. Additionally, the surface spectral reflectance and bidirectional reflectance distribution function (BRDF) were obtained from the field campaign at Chaidamu Basin, 2018. To demonstrate the practical utilization and usability of these PICSs, they were employed in the multi-site top of atmosphere (TOA) reflectance simulation to validate the operational calibration performance of Aqua/MODIS and FY-3D/MERSI-II (Medium Resolution Spectral Imager II). The simulation results showed good consistency compared with the observations from both MODIS and MERSI-II, with a relative bias and root mean square error (RMSE) of <5% and <0.05%, respectively. These sites provide prospects for multi-site vicarious calibrations of solar reflective bands, which may help to evaluate or characterize instrumental nonlinear responses using a wider signal dynamic from the sites in different seasons.

Facile deposition of nanostructured Rhodamine-6G/FTO optical system thin films for optical limiting

Thin films of Rhodamine-6G were fabricated with different thicknesses by utilizing the spin-coating technique. The used substrate was the Fluorine-doped tin oxide (FTO) for deposition the studied films on it. The technique of X-ray diffraction (XRD) was applied to detect the structural properties of the investigating Rhodamine-6G/FTO thin films. The analysis of Rhodamine 6G/FTO film surface morphology was achieved by the aid of the atomic force microscopy (AFM) technique. Spectral distribution of transmittance, reflectance, and absorbance in the wavelength range (300–2500 nm) was used to explore both of linear properties in addition to the nonlinear optical characteristics of Rhodamine-6G/FTO. All the investigated samples appeared to have an indirect allowed transition. The parts of the complex dielectric constants, real and imaginary parts, were specified. Further, the third-order nonlinear susceptibility (χ(3)) and the nonlinear refractive index (n2) were estimated. The optical limiting was examined using laser; He–Ne of 632.8 nm and solid-state green of 533 nm. It was found that the normalized power increased with decreasing the thickness of the Rhodamine 6G/FTO thin films. Rhodamine 6G/FTO is a promising optical system for optoelectronic applications.

Morphology induced spectral reflectance lineshapes in VO2 thin films

In this work, we study the spectral reflectance of VO2 thin films and identify the specific contributions of the morphology and phase transition to optical spectra. The formation of highly [011] textured VO2 thin films on Si was achieved by an oxidation process starting with a metallic V thin film grown on an [001] Si substrate by an evaporation technique. Structural (XRD and Raman) and spectroscopic (XPS) characterization results indicate high purity VO2 formation with different sizes at various annealing temperatures without any change in the composition. Temperature dependent spectral reflectance distributions reveal that the insulator-to-metal transition (IMT) phase transition temperature of the VO2 nanostructures shows a slight size-dependence (∼3 °C), but this feature can be overshadowed by morphology that can lead to the misinterpretation of transition characteristics. The spectral line shape of the reflectance curves in the visible and near-infrared regions show substantially different characteristics for the samples annealed at different temperatures. Using numerical scattering calculations, we conclude that the changes in the optical response can be explained by morphological effects instead of changes in the intrinsic material properties such as a shift in the IMT temperature. Furthermore, the main mechanism leading to different spectral line shapes is the morphological differences leading to diffuse and specular reflectance.

Soil directioal (biconical) reflectance in the principal plane with varied illumination angle under dry and saturated conditions.

Change in directional (biconical) spectral reflectance was monitored for three soil samples under air dry and saturated conditions in the laboratory. The illumination angle was set consecutively at θi = -10°, -40°, and -70° (left side of the sample on the principal plane), while the observation angle ranged from θo = -60° to + 60° (both sides of the sample in the principal plane) in 5° increments. The soil samples were chosen to represent a variety of soil properties. Emphasis is on observations that illustrate the changes in the directional and spectral distribution of soil reflectance when the soil is dry or saturated.

Reflectance reference target at Järvselja, Estonia for the calibration of optical remote sensing sensors and lessons learned

A calibration target for the support of airborne and satellite measurements was built at the Järvselja site for ecological and remote sensing studies located in southeastern Estonia. The calibration target is a 10 × 10 m concrete panel which is protected by a removable roof. Optical properties of the panel are carefully studied in order to serve as a reference in spectroscopic remote sensing measurements. In this study we report the spectral distribution of reflectance in the wavelength range of 350–2500 nm, the angular distribution of directional reflectance and the linear polarization of the reflected radiation. The reflectance spectrum of the panel is smooth in the visible and NIR wavelengths but with steep decrease at wavelengths less than 400 nm. Variations of reflectance over the panel surface are less than 1%. The radiation is partly polarized in forward scattering direction. No temporal changes of optical properties have been observed. The calibration target improves the metrological quality of airborne spectral measurements at the Järvselja test site and neighboring areas. It can also be used for ground truth to aid the validation of adjacency correction algorithms for data from high spatial resolution satellite images, as well as a reference for the registration of airborne and satellite images. It can also serve as an elevation reference for both lidar and radar altimeter measurements.

Object discrimination in poultry housing using spectral reflectivity

To handle surrounding objects, autonomous poultry house robots need to discriminate between various types of object present in the poultry house. A simple and robust method for image pixel classification based on spectral reflectance properties is presented. The four object categories most relevant for the autonomous robot PoultryBot are eggs, hens, housing elements and litter. Spectral reflectance distributions were measured between 400 and 1000 nm and based on these spectral responses the wavelength band with lowest overlap between all object categories was identified. This wavelength band was found around 467 nm with an overlap of 16% for hens vs. eggs, 12% for housing vs. litter, and less for other combinations. Subsequently, images were captured in a commercial poultry house, using a standard monochrome camera and a band pass filter centred around 470 nm. In 87 images, intensity thresholds were applied to classify each pixel into one of four categories. For eggs, the required 80% correctly classified pixels was almost reached with 79.9% of the pixels classified correctly. For hens and litter, 40–50% of the pixels were classified correctly, while housing elements had lower performance (15.6%). Although the imaging setup was designed to function without artificial light, its optical properties influenced image quality and the resulting classification performance. To reduce these undesired effects on the images, and to improve classification performance, artificial lighting and additional processing steps are proposed. The presented results indicate both the simplicity and elegance of applying this method and are a suitable starting point for implementing egg detection with the robot.

Evaluating visibility of age spot and freckle based on simulated spectral reflectance distribution and facial color image

In this research, we evaluate the visibility of age spot and freckle with changing the blood volume based on simulated spectral reflectance distribution and the actual facial color images, and compare these results. First, we generate three types of spatial distribution of age spot and freckle in patch-like images based on the simulated spectral reflectance. The spectral reflectance is simulated using Monte Carlo simulation of light transport in multi-layered tissue. Next, we reconstruct the facial color image with changing the blood volume. We acquire the concentration distribution of melanin, hemoglobin and shading components by applying the independent component analysis on a facial color image. We reproduce images using the obtained melanin and shading concentration and the changed hemoglobin concentration. Finally, we evaluate the visibility of pigmentations using simulated spectral reflectance distribution and facial color images. In the result of simulated spectral reflectance distribution, we found that the visibility became lower as the blood volume increases. However, we can see that a specific blood volume reduces the visibility of the actual pigmentations from the result of the facial color images.

Optical dispersion parameters and stability of poly (9, 9′-di-n-octylfluorenyl-2.7-diyl)/ZnO nanohybrid films: towards organic photovoltaic applications

Conjugated polymer nanohybrid films were prepared from poly (9,9′-di-n-octylfluorenyl-2.7-diyl) (PFO) and zinc oxide (ZnO) nanoparticles. ZnO nanopowder was prepared by the solgel method, different ratios of PFO/ZnO nanohybrids have been prepared using solution blending method. Then, the blends were spin-coated onto glass substrates at 2000 rpm for 1 min. and subsequently dried at room temperature. XRD and TEM were used to determine the structural properties, while UV–Vis and photoluminescence spectrophotometers were employed to investigate the optical properties of the films. The spectral distribution of specular reflectance were used to calculate the refractive index n (λ) and the optical dispersion parameters were determined according to Wemple and Didomenico (WD) model. The effect of ZnO NPs on the direct and indirect band gap energies, photo- and thermal stability was also discussed. A significant enhancement in the light emitting properties has been observed by increasing the concentration of ZnO NPs.

Electromagnetic resonance modes on a two-dimensional tandem grating and its application for broadband absorption in the visible spectrum.

In this work, we numerically investigate the electromagnetic resonances on two-dimensional tandem grating structures. The base of a tandem grating consists of an opaque Au substrate, a SiO(2) spacer, and a Au grating (concave type); that is, a well-known fishnet structure forming Au/SiO(2)/Au stack. A convex-type Au grating (i.e., topmost grating) is then attached on top of the base fishnet structure with or without additional SiO(2) spacer, resulting in two types of tandem grating structures. In order to calculate the spectral reflectance and local magnetic field distribution, the finite-difference time-domain method is employed. When the topmost Au grating is directly added onto the base fishnet structure, the surface plasmon and magnetic polariton in the base structure are branched out due to the geometric asymmetry with respect to the SiO(2) spacer. If additional SiO(2) spacer is added between the topmost Au grating and the base fishnet structure, new magnetic resonance modes appear due to coupling between two vertically aligned Au/SiO(2)/Au stacks. With the understanding of multiple electromagnetic resonance modes on the proposed tandem grating structures, we successfully design a broadband absorber made of Au and SiO(2) in the visible spectrum.

Investigation of the spectral reflectance and bidirectional reflectance distribution function of sea foam layer by the Monte Carlo method.

Spectral properties of sea foam greatly affect ocean color remote sensing and aerosol optical thickness retrieval from satellite observation. This paper presents a combined Mie theory and Monte Carlo method to investigate visible and near-infrared spectral reflectance and bidirectional reflectance distribution function (BRDF) of sea foam layers. A three-layer model of the sea foam is developed in which each layer is composed of large air bubbles coated with pure water. A pseudo-continuous model and Mie theory for coated spheres is used to determine the effective radiative properties of sea foam. The one-dimensional Cox-Munk surface roughness model is used to calculate the slope density functions of the wind-blown ocean surface. A Monte Carlo method is used to solve the radiative transfer equation. Effects of foam layer thickness, bubble size, wind speed, solar zenith angle, and wavelength on the spectral reflectance and BRDF are investigated. Comparisons between previous theoretical results and experimental data demonstrate the feasibility of our proposed method. Sea foam can significantly increase the spectral reflectance and BRDF of the sea surface. The absorption coefficient of seawater near the surface is not the only parameter that influences the spectral reflectance. Meanwhile, the effects of bubble size, foam layer thickness, and solar zenith angle also cannot be obviously neglected.

An imaging spectrophotometer for measuring the two-dimensional distribution of spectral reflectance

We present a novel instrumentation scheme for measuring the two-dimensional distribution of spectral reflectance based on the spectral imaging technique. It takes digital spectral images of a test sample using a LED-based monochromatic integrating sphere source and a monochrome CCD camera. We developed a calibration algorithm to assign the digital counts of the images to the reflectance values at each wavelength. The measurement uncertainty is evaluated to be less than 1.5% (k = 2) for high-reflectance samples (with reflectance ⩾0.4) and less than 3% (k = 2) for low-reflectance samples (with reflectance <0.4). For a validity test, we demonstrate an agreement with the results of a reference spectrophotometer within 1% for high-reflectance samples or within 2% for low-reflectance samples. This scheme of ‘imaging spectrophotometer’ is promising to measure the spatially resolved spectral reflectance of complex samples only by a single wavelength scan.

Parallel phase-shifting digital holography using spectral estimation technique.

We propose a parallel phase-shifting digital holography using a spectral estimation technique, which enables the instantaneous acquisition of spectral information and three-dimensional (3D) information of a moving object. In this technique, an interference fringe image that contains six holograms with two phase shifts for three laser lines, such as red, green, and blue, is recorded by a space-division multiplexing method with single-shot exposure. The 3D monochrome images of these three laser lines are numerically reconstructed by a computer and used to estimate the spectral reflectance distribution of object using a spectral estimation technique. Preliminary experiments demonstrate the validity of the proposed technique.

Changes in Vertical Distribution of Spectral Reflectance within Spring Barley Canopy as an Indicator of Nitrogen Nutrition, Canopy Structure and Yield Parameters

Abstract The main objective of this study was to evaluate the spectral reflectance in the vertical profile of spring barley canopy at the booting growth stage and to determine how the reflectance gradient changes in relation to crop density and nitrogen (N) nutrition. Vertical gradients of spectral reflectance were studied in field trials with three sowing densities (2, 4 and 6 million of germinating seeds/ha) and two levels of N nutrition (0 and 90 kg/ha). It was found that differences in vegetation indices caused by N nutrition are most pronounced in the second and third leaf from the top, and these increase with increasing sowing density. The vertical gradient of reflectance, specifically the ratio between the leaves F-3/F-1 for vegetation indices based on red-edge reflectance, represents a reliable indicator of number of ears per area unit (R = –0.87 for Normalised Red Edge-Red Index (NRERI) and –0.93 for Zarco-Teja-da and Miller Simple Ratio Index (ZM)). A close relationship to ear productivity was found almost for all observed vegetation indices and any leaf in vertical profile (R = 0.79–0.97). In contrast, the prediction of protein content in barley grain was the most reliable when the red-edge reflectance indices (ZM and NRERI) particularly from upper three leaves were used (R = 0.81–0.88). The results show that the knowledge of reflectance heterogeneity in the vertical profile of canopy can significantly contribute to the interpretation of the measured data, to the differentiation of the N nutrition effect from the response to canopy density, and finally to a more accurate estimation of yield parameters and protein content in grain.

Digital Holography Using Spectral Estimation Technique

We propose a technique capable of obtaining spectral information and three-dimensional information of objects. This technique is based on digital holography and spectral estimation technique. In this technique, multiple lasers operating at different wavelengths, such as red, green, and blue, are used to record the complex amplitude of the object in digital holography, and multiple reconstructed monochrome images can be obtained by each wavelength. Spectral estimation technique is used to estimate the spectral reflectance distribution of the object from the multiple reconstructed monochrome images. Through the spectral estimation technique, the spectral reflectance distribution of object can be obtained. The effectiveness of the proposed method was confirmed by a numerical simulation and an experiment.

Functional Data Analysis of Multi-Angular Hyperspectral Data on Vegetation

Abstract - The surface reflectance anisotropy can be estimated by directional reflectance analysis through the collection of multi-angular spectral data. Proper characterization of the surface anisotropy is an important element in the successful interpretation of remotely sensed signals. A signal received by a sensor from a vegetation canopy is affected by several factors. One of them is the sensor zenith angle. Functional data analysis can be used to assess the distribution and variation of spectral reflectance due to sensor zenith angle. This paper examines the effect of sensor zenith angles on the spectral reflectance of vegetation, example on cotton leaves. The spectra were acquired in a green house trial in order to address the question ‘how much information can be obtained from multi-angular hyperspectral remote sensing on vegetation?’ The goals of the functional data analysis applied in this paper is to examine the Functional Data Analysis approach was applied to analysis multi-angular hyperspectral data on cotton, highlighting various characteristics of cotton spectra due to sensor view angles, and to infer directional variation in an outcome or dependent variable with different zenith angles.

Analysis of Hyperspectral Images Based on PCA

Recent computational models of color vision demonstrate that it is possible to achieve exact color constancy over a limited range of lights and surfaces described by a low-dimensional linear model. For smooth reflectance spectra the different spectral bands have a significant degree of correlation. Any spectral reflectance distribution can be approximated to a specified degree of accuracy as a weighted sum of basis functions. Reflectance spectra of hyperspectral images of the natural scenes are supposed to represent the real world better than any certain classes of natural and man-made spectral reflectance data sets such as rocks, leaves, Munsell chips, etc. The characteristics of the spectra will be important to understand the spectral properties of the object reflectance and the representation of spectral images by linear models. In this study sets of hyperspectral images have been analyzed by principal-component analysis (PCA) method for spectral encoding.

416 ヒト皮膚画像における色差に基づく分光反射率の空間分布解析(バイオエンジニアリングII)

416 ヒト皮膚画像における色差に基づく分光反射率の空間分布解析(バイオエンジニアリングII)