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Monte Carlo integration is an established method in simulating light transport. However, due to its stochastic nature, it requires copious amounts of samples to eliminate the estimation error, and variance reduction techniques such as importance sampling are used to improve the convergence speed as a remedy. Path guiding is a class of adaptive importance sampling methods devised specifically for light transport simulation, which demonstrates significant improvements over classical sampling techniques. Yet most of the previous path guiding methods only account for the radiance term, omitting the bidirectional scattering distribution function (BSDF) term. This results in suboptimal sample quality for non-diffuse light transport. This paper presents a path guiding method which guides paths according to the full product of the BSDF and radiance terms in light transport equation. Extending a spatio-directional tree based path guiding method, we use a semi-adaptive grid-quadtree hybrid subdividing the directional domain in a spatial subdomain to learn and represent the radiance field. With the help of BSDF lookup tables used to accelerate BSDF evaluations, this grid-quadtree allows us to efficiently construct approximate product distributions and guide paths according to the product of incident radiance and cosine-weighted BSDF at each path vertex. The resulting method is relatively simple to implement and enables more robust sampling on scenes with many glossy surfaces.

Aiming to explore its performance as energy efficient system, in this study, the window is subdivided according to functions, in which the upper part would act as a daylight optimization unit. Two variant positions of lasercut panel, known as ‘louvre-style’ and ‘venetian-style’ are placed in the upper window unit, in order to take advantage of their angle selective redirecting capabilities. Their effectiveness to provide a satisfactory visual comfort is evaluated by assessing their potential for solar control and daylight redirection indoors. The first results indicate that the use of lasercut panel as a sole system, its insufficient to provide an adequate visual environment, with a reduced risk of glare for the occupants. Aiming to improve its performance, horizontal blinds are added as supplementary element to the interior-upper part of the window, blended in an arrangement called ‘secondary system’. As a result of a comprehensive evaluation, in which, the upper and middle window units are considered, two lasercut panel styles are identified as those providing sufficient daylight provision indoors, and a reduced risk of discomfort glare. The properties of the fenestration systems tested here, were described using their corresponding BSDF data, while the evaluation was performed using the RADIANCE matrix multiplication methods.

Fused silica diffusers, made by forming scattering centers inside fused silica glass, can exhibit desirable optical properties, such as reflectance or transmittance independent of viewing angle, spectrally flat response into the ultraviolet wavelength range, and good spatial uniformity. The diffusers are of interest for terrestrial and space borne remote sensing instruments, which use light diffusers in reflective and transmissive applications. In this work, we report exploratory measurements of two samples of fused silica diffusers. We will present goniometric bidirectional scattering distribution function (BSDF) measurements under normal illumination provided by the National Institute of Standards and Technology (NIST)’s Goniometric Optical Scatter Instrument (GOSI), by NIST’s Infrared reference integrating sphere (IRIS) and by the National Aeronautics and Space Administration (NASA)’s Diffuser Calibration Laboratory. We also present hemispherical diffuse transmittance and reflectance measurements provided by NIST’s Double integrating sphere Optical Scattering Instrument (DOSI). The data from the DOSI is analyzed by Prahl’s inverse adding-doubling algorithm to obtain the absorption and reduced scattering coefficient of the samples. Implications of fused silica diffusers for remote sensing applications are discussed.

Fractal and polarization analysis of diffusively scattered light is applied to determine the complex relationship between fractal dimension of structural morphology and concentration of chemically active ingredients in two pharmaceutical mixture systems including a series of binary mixtures of acetaminophen in lactose and three multicomponent blends with a proprietary active ingredient. A robust approach is proposed to identify and filter out multiple- and single-scattering components of scattering indicatrix. The fractal dimension extracted from scattering field reveals complex structural details of the sample, showing strong dependence on low-dose drug concentration in the blend. Low-angle diffraction shows optical “halo” patterns near the angle of specular reflection caused by light refraction in microcrystalline aggregates. Angular measurements of diffuse reflection demonstrate noticeable dependence of Brewster's angle on drug concentration. It is shown that the acetaminophen microcrystals produce scattered light depolarization due to their optical birefringence. The light scattering measurement protocol developed for diffusively scattered light by microcrystalline pharmaceutical compositions provides a novel approach for the pattern recognition, analysis and classification of materials with a low concentration of active chemical ingredients.

A screen image synthesis (SIS) system is superior than the conventional methods in terms of high-speed measurement and low screen-cross-talk noise when used as a whole-field light-distribution meter. However, reflection signals cannot be measured using the conventional SIS system when it is used as a scattering meter. Furthermore, the conventional SIS system cannot be used to measure a large sample when it is used as an intensity distribution meter. In this study, we devised a rail-based SIS system as long as an image reconstruction algorithm. This would allow whole-field scattering light and intensity distribution measurements for various sample sizes. For this purpose, a versatile instrument was assembled by combining a whole-field intensity distribution meter and a whole-field scattering meter. The results of the experiments confirmed that the measuring time was drastically improved when the proposed instrument was used as a whole-field intensity distribution meter and a whole-field scattering meter. The high normalized cross correlation values of both measurements demonstrated the accuracy and feasibility of the proposed algorithm.

Fluorescent materials can shift energy between wavelengths, thereby creating bright and saturated colors both in natural and artificial materials. However, rendering fluorescence for continuous wavelengths or combined with wavelength dependent path configurations so far has only been feasible using spectral unidirectional methods. We present a regularization-based approach for supporting fluorescence in a spectral bidirectional path tracer. Our algorithm samples camera and light sub-paths with independent wavelengths, and when connecting them mollifies the BSDF at one of the connecting vertices such that it reradiates light across multiple wavelengths. We discuss arising issues such as color bias in early iterations, consistency of the method and MIS weights in the presence of spectral mollification. We demonstrate our method in scenes combining fluorescence and transport phenomena that are difficult to render with unidirectional or spectrally discrete methods.

Simulation with two types of bi-directional scattering distribution function (BSDF) was used to model the prism daylight redirecting fenestration (PDRF) in the indoor luminous environment. A goniophotometer was used to develop two different BSDF data sets: Klems data and Tensor tree data. Coefficient of determination and linear regression of the illuminance values with Klems and Tensor tree BSDF data were analyzed at low, medium, and high solar altitudes under Perez sky models with various sky conditions. The comparisons indicate that the Klems and Tensor tree angular data of PDRF materials show strong correlations and good linear regression relationships in general with PDRF daylighting clerestories. The study results demonstrated that using measured Klems data for combined daylighting and energy simulation of PDRF system is feasible as the simulated illuminance levels with Klems and Tensor tree data are similar under Perez sky conditions. The simulation results also showed that the PDRF daylighting windows above vision windows increase the work plane illuminance (WPI) opposite the window wall under clear sky conditions.

The bidirectional scattering distribution function (BSDF) describes how light is scattered on a surface. Microfacet-based BSDF models assume that surfaces are a collection of randomly oriented microfacets, describe the distribution probabilities of these microfacets, and plausibly approximate their reflective properties using parameterized expressions. Traditional analytic microfacet models, such as Cook–Torrance (CT) and the Oren–Nayar (ON), ignore the effects of diffraction. The Cook–Torrance diffraction model (CTD) combines the traditional Cook–Torrance model with diffraction effects to better approximate the measured reflectance. However, the effects of diffuse diffraction are ignored in this two-layer microfacet reflectance model. In this paper, We propose a two-layer microfacet reflectance model that combines the effects of specular diffraction with those of diffuse diffraction. The upper layer of our model is the Cook–Torrance microfacet model with diffraction, while the lower layer is the Oren–Nayar microfacet model that considers the effects of diffuse diffraction. Our model yields a better approximation than the CTD model, especially for plastic-like multi-layer materials. In contrast to previous models where the effects of diffraction cannot be controlled, those of our model can be easily manipulated by the coefficient of diffraction roughness. The proposed OND model is based on three techniques: precomputation, convolution computation, and the Gauss–Newton method.

This paper proposes a lightweight bidirectional scattering distribution function (BSDF) model for layered materials with anisotropic reflection and refraction properties. In our method, each layer of the materials can be described by a microfacet BSDF using an anisotropic normal distribution function (NDF). Furthermore, the NDFs of layers can be defined on tangent vector fields, which differ from layer to layer. Our method is based on a previous study in which isotropic BSDFs are approximated by projecting them onto base planes. However, the adequateness of this previous work has not been well investigated for anisotropic BSDFs. In this paper, we demonstrate that the projection is also applicable to anisotropic BSDFs and that the BSDFs are approximated by elliptical distributions using covariance matrices.

Remote sensing provides high accuracy/precision for quantifying forest biophysical parameters needed for ecological management. Although the significant impact of bidirectional scattering distribution functions (BSDFs) on remote sensing of vegetation is well known, current forest metrics derived from sensor data seldom take leaf BSDF into account, and despite the importance of BSDF effects, leaf directional scattering measurements are almost nonexistent. Previous studies have been limited in the spectral coverage and resolution of observed electromagnetic radiation and lacked models to interpolate all source-sensor angles beyond measurements. This study captured deciduous broadleaf bidirectional reflectance distribution functions (BRDFs) from the visible through shortwave infrared spectral regions (350–2500 nm) and accurately modeled the BRDF for extension to any illumination angle, viewing zenith, or azimuthal angle. We measured biconical directional reflectance factor of leaves from three species of large trees, Norway maple (Acer platanoides), American sweetgum (Liquidambar styraciflua), and northern red oak (Quercus rubra). We then fit the data through nonlinear regression to physical, microfacet BRDF models, resulting in normalized root-mean-square errors of less than 8%, averaged across all wavelengths (excluding low signal-to-noise spectral regions). We extracted leaf physical parameters, including the index of refraction and a relative physical roughness from the microfacet models delineating the three species. The implications for forestry remote sensing are important, as rigorous models to represent leaves allow for the creation of more accurate forest scenes for radiative transfer modeling. Such accuracy enables higher fidelity sensor evaluations and data processing algorithms.

Daylight simulation at the Competence Centre Building Envelopes and Civil Engineering at Lucerne University of Applied Sciences and Arts.

In this work, a CCD-augmented complete angle scatter instrument (CASI) with a visible red laser source was used to measure the BRDF of a commercially available solar cell designed for small satellites, simultaneously capturing both in-plane and out-of-plane data with high angular resolution surrounding the specular direction. The measurements exhibited three distinct scatter features: a central specular peak, an offset specular peak, and a diffraction pattern. The two peaks were caused by different material surfaces with slightly different normal directions, and the diffraction pattern arose from periodically-spaced metal conducting bars running in one direction across the solar cell surface. The diffraction pattern measurements were verified in-plane with an original single-pixel CASI detector and then used to inform the creation of a single closed-form BRDF model capable of describing the out-of-plane features. Both specular peaks were modeled using a traditional microfacet formulation, but the offset peak model implemented a rotation of the incident and scatter directions to account for the difference in surface normal direction. The diffraction pattern–which is not typically described with microfacet models–was described based on Fraunhofer diffraction through two rectangular stripes, adjusted in terms of microfacet coordinates. Parameters for the model were chosen manually, based largely on physical material properties when possible, rather than using optimized fitting algorithms. Model results were compared to the measurements by using the same CCD pixel scatter coordinates. Qualitatively, the model successfully replicated the observed features, and quantitatively, the modeled peak values agree with the measurements within an order of magnitude.

The cheapest method for an instrument to perform radiometric monitoring in orbit is to compare its radiometric response from a scene to the known radiance of that same scene. This is known as vicarious calibration. The known radiance of this scene comes mostly from other space instruments. The limiting factors of this vicarious calibration approach arise from differences in the acquisition time and illumination/viewing geometry between the two measurements. Earth scenes may change over time, which limits vicarious calibration to quasi stable scenes. The level of stability of these scenes limits the level of accuracy that can be achieved. Likewise, the bi-directional scattering distribution function (BSDF) of the observed scene is likely to cause differences in observed radiance if the illumination and/or viewing geometry changes. If the observation of the scene is at the same time, stability of the scene is no longer an issue, and if the observation is at the same geometry then BSDF effects will cancel, and direct comparison is possible. This is rarely the case unless the instrument is on the same satellite. In this paper we present the design and measurement concept of such a small, on-board calibration instrument; the Absolute Radiometric Reference Instrument (ARRI). We believe this concept will revolutionize the approach to in-orbit absolute reflectance calibration.

The objects with microroughness surfaces, heterogeneous media are widely used in modern optical devices, for instance in various light guiding devices, car dashboards and other illuminating systems as elements of scenes aimed to generate images with photorealistic quality. Surface or volume scattering of these objects can have very complex shape with pronounced picks, far from ideal specular or ideal diffuse ones and typically described with Bi-Directional Scattering Functions (BSDF). If model reconstructing BSDF measuring device contains inaccurateness, it can result in errors of parameters reconstruction for scattering objects and serious damage for entire optical simulation for scattering objects. In simulation model it is very preferable simulate optical parts maximally close to real measuring device. Another problem is calculation speed of model aimed for BSDF simulation. BSDF measurement devices have very high angular and spatial resolutions that results in a very ineffective from viewpoint of simulation. Moreover, BSDF functions is multidimensional, so many calculations are required to fulfill. These problems impose careful choosing of simulation model, its reasonable simplifications, selection of proper ray tracing engine. In the paper the virtual prototyping of different industrial measurement devices is considered. These devices are quite different and thus require different approaches in computer models design. The results of virtual prototyping for several samples with complex scattering properties are presented as in numerical shape of angular intensity distribution as well in qualitative as photorealistic images. All virtual prototyping simulated results are compared with measurements to prove reliability and reasonability of built models.

In the design and specification of precision optical components for advanced imaging applications it is necessary that residual optical fabrication errors be specified and measured over the “entire range of relevant spatial frequencies”. This includes the mid-spatial-frequency surface errors that span the gap between the traditional “figure” and “finish” errors. Since surface scatter is merely a diffraction phenomenon, the linear systems formulation of non-paraxial scalar diffraction theory forms the basis of the GHS surface scatter theory: a linear systems formulation of surface scatter theory valid for smooth or rough surfaces, large or small incident and scattered angles and arbitrary surface PSDs. The resulting surface transfer function can be combined with the conventional OTF which then characterizes image degradation due to diffraction effects, geometrical aberrations, and surface scatter effects. The method of determining the composite surface PSD from the metrology data and the method of predicting the bidirectional scattered distribution function (BSDF) from the surface PSD will be discussed as will the process for deriving the optical fabrication tolerances necessary for satisfying specific image quality requirements.

International audience; A statistical multi-lobe approach was recently introduced in order to efficiently handle layered materials rendering as an alternative to expensive general-purpose approaches. However, this approach poorly supports scattering volumes as the method does not account for back-scattering and resorts to single scattering approximations. In this paper, we address these limitations with an efficient solution based upon a transfer matrix approach which leverages the properties of the Henyey-Greenstein phase function. Under this formalism, each scattering component of the stack is described through a lightweight matrix, layering operations are reduced to simple matrix products and the statistics of each BSDF lobe accounting for multiple scattering effects are obtained through matrix operators. Based on this representation, we leverage the versatility of the transfer matrix approach to efficiently handle forward and backward scattering which occurs in arbitrary layered materials. The resulting model enables the reproduction of a wide range of layered structures embedding scattering volumes of arbitrary depth, in constant computation time and with low variance.

With the rapid development of high-resolution synthetic aperture radar (SAR) in spaceborne remote sensing and ground-based applications, SAR as a microwave imaging device could easily acquire images of decimeter to centimeter resolution showing the texture features of rough surface, and facilitate the image texture modeling to better interpret the underlying mechanism. Conventional analytical scattering models for rough surface are tailored for non-imaging scatterometers and cannot model the SAR image texture of rough surface. Inspired by the bidirectional reflection distribution function (BRDF) of rough surface in computer graphics which is spatially focused, we propose the coherent spatially varying bidirectional scattering distribution function (CSVBSDF) of finite-size rough surface for SAR images. It is analytically derived based on the integral equation model (IEM) model and resembles the spatially varying bidirectional scattering distribution function (SVBSDF). Given roughness parameters of the rough surface, the CSVBSDF can generate a SAR image quickly. Comparison of the scattering coefficient and the SAR image with numerical simulation method show that the proposed model is in good agreement with numerical method.

Stray laser light is a serious problem that interrupts the measurement of electron temperature and density in Thomson scattering (TS) systems. This paper presents a ray-tracing simulation of stray laser light in HL-2M TS systems. A model including (i) a simplified laser-beam injection system, (ii) the scattered-light collection systems for central-point TS (CPTS) and edge TS (ETS), and (iii) the HL-2M vessel is built using the TracePro and CATIA software packages based on measurements of the bidirectional scattering distribution function at a wavelength of 532 nm. The simulation results show that no stray laser light reaches the injection surface of the collection lens of the CPTS system, and only a few stray laser rays of all the rays reaching the injection surface of the collection lens of the ETS system can be collected when the energy threshold per ray is 1 × 10−16. The stray laser rays that reach the scattered-light collection systems are mainly from the first and second parts of the slides of the beam dump, so decreasing the roughness of those parts could be effective in reducing the level of stray laser light.

The environmental trace gas monitoring instrument (EMI) is a space-borne imaging spectrometer onboard GaoFen-5, which was launched in May 2018, covering wavelengths in the range of 240–710 nm to measure NO2, O3, HCHO, and SO2. An advanced EMI-2 instrument with a higher spatial resolution and sufficient signal-to-noise is currently planned for launch on the GaoFen-5(02) satellite in 2021. The EMI-2 instrument bidirectional scattering distribution function (BSDF) is obtained from the absolute irradiance and radiance calibration on-ground. Based on EMI-2 earth and sun optical paths, the key factors of BSDF parameters are introduced. An NIST-calibrated 1000 W FEL quartz tungsten halogen lamp and a 2D turntable are adopted for the absolute irradiance calibration. A large aperture integrating sphere system is used for the absolute radiance calibration. Based on absolute irradiance and radiance calibration functions, the BSDF parameters are obtained, with accuracy of 4.9% for UV1, 4.3% for UV2, 4.1% for VIS1, and 4.2% for VIS2. The on-ground measurement results show that the reflectance spectrum can be calculated from BSDF parameters. On-orbit application of the EMI-2 instrument BSDF are also discussed.

Data-driven models replicate the irregular Bidirectional Scattering Distribution Functions (BSDFs) of optically Complex Fenestration Systems in daylight simulation. RADIANCE employs the ten...

Microfacet distributions are considered nowadays as a reference for physically plausible BSDF representations. Many authors have focused on their physical and mathematical correctness, while introducing means to enlarge the range of possible appearances. This article is dedicated to Normal Distribution Functions (NDFs) and the influence of their shape on the rendered material aspect. We provide a complete framework for studying the impact of NDFs on the observed Bidirectional Scattering Distribution Functions (BSDFs). To explore very general NDFs, manually controlled by the user, and including anisotropic materials, we propose to use a piecewise continuous representation. It is derived with its associated Smith shadowing-masking function and importance sampling formulations for ensuring efficient global illumination computations. A new procedure is also proposed in this article for generating an explicit geometric micro-surface, used to evaluate the validity of analytic models and multiple scattering effects. The results are produced with a computer-generated process using path tracing. They show that this generation procedure is suitable with any NDF model, independently from its shape complexity.

The pattern and permeability characteristics that compose three-dimensional (3D) textiles are important as a textile shading component to the architecture, engineering and construction (AEC) industry. Moreover, due to their complex geometry, 3D fabrics require a detailed modeling for correct evaluation of performance. This paper aims to present and investigate the optical properties of six 3D fabrics proposed as an alternative to traditional roller blind shading systems, which could guarantee high daylight availability and visual comfort. The light transmission distribution for the different samples has been characterized by carrying out angular visual transmittance measurements, using integrating sphere optical benches, and virtual modeling using Radiance's genBSDF tool. The Bidirectional Scattering Distribution Function (BSDF) calculated with Radiance shows a good fit with the optical angular measurements, which were used as a benchmark and to calibrate models. The performance of the 3D textiles, in terms of illuminance, daylight availability, and glare, was assessed considering two of the set of 3D textiles as alternative materials for a movable internal roller shade system in an open office. The innovative system was compared with a traditional single layer fabric roller blind under different shading control strategies, 3D fabrics demonstrate the potential of increasing Daylight Autonomy while providing better uniformity and better connection with the outdoors due to a higher openness factor. The shading effect created by the 3D geometry of the textile can increase the openness factor while restricting glare.

In this work, three dimensional periodic ordered opal structures are used to model the inner structures of skeleton of porous ceramic foam. The radii of close-packed spheres range from 0.7 µm to 1.7 µm. The spectral radiative properties are predicted by applying the FDTD method to analyze the radiative transfer inside the skeleton. The characteristics of reflection spectra and transmission spectra with increasing incident wavelength are analyzed, including the different feature regions constituting the variation curves and the red shift of variation curve with growing size of close-packed spheres. The values and characteristics of absorption peaks surrounding the locations where size parameters are approximate to 1 are compared. The BSDF of scattering power are calculated further. The transformation of transmission in incident direction and reflection in mirror direction is shown. Then, the distribution of radiation intensity in cross sections parallel to the incident light are compared and the variety from uniform distribution to anisotropic periodic distribution is summarized. The prediction and analysis are benefit to further researches about the radiative transfer inside the porous ceramic foam.

In optics, elements with complex light scattering properties are typically simulated either with the computer models based on the reconstruction of their surface and internal structure or with measured Bi-Directional Scattering Distribution Function (BSDF) which totally describes the dependence of scattering properties on illumination and observation conditions. However, in many cases simulation of precise computer models to specify light scattering properties is impossible because parameters either not available or measured with insufficient accuracy. The approach based on measured BSDF is not applicable in all cases also, for instance, when it is necessary to make a simulation of some light guiding plate (LGP) with rough scattering surfaces. In this case, the properties of light scattering on the rough surfaces should be specified and thus measured separately from the whole LGP. The BSDF for such kinds of surfaces is either impossible to measure at all, or measurements are very expensive due to the need to use additional and very complex equipment. The article considers the third alternative approach to simulate scattering properties based on the reconstruction of the whole BSDF with an optimization process. The objective function is an angular intensity distribution measured with GP-200 goniophotometer. Another problem is the calculation speed of the simulated model. BSDF is a multidimensional function and its calculation with proper resolution can be a difficult task. This work proposes a fast and simple way to simulate the angular intensity distribution of scattering material based on BSDF obtained with a measuring device. The simulation results based on several examples of scattering samples are compared with real measurements.

Straylight requirements for optical instruments become ever more stringent. This applies not only to optical instruments in space, but also extends to optical ground support equipment (OGSE) and any other instrument that is sensitive to straylight. One of the means to control the straylight within instruments and OGSE’s is the application of black coatings, e.g. on optical mounts, lens barrels and baffles. There are different types of black coatings on the market. The choice of a suitable black coating does not only depend on its optical properties, but also on the compatibility with the substrate material and its geometry. For many coatings, the manufacturers provide only a hemispherical reflectivity value, which is not very suitable for straylight predictions, as it does not include the angle dependent scattering behavior. This information is provided by the Bi-directional Scatter Distribution Function (BSDF). The optics and opto-electronics laboratories (OOEL) at ESTEC receive many requests to characterize black coatings by measuring the BSDF. The OOEL has created a database for black coatings to collect the BSDF data in support to space industry to facilitate the selection of the most suitable black coating and make more accurate predictions of straylight at instrument level. The database, called ‘Black Coatings BSDF Database’, will be presented here to showcase its functionalities. We will present some examples of BSDF data to demonstrate the added value over hemispherical reflectivity. The BSDF data contained within the Black Coatings BSDF Database is structured according to coating type, measured wavelength and, if that information was available, according to specific information on the coating and/or substrate. So far, all BSDF measurements data has been measured at the OOEL using the two currently available CASI and Albatross TT scatterometers. Additional data will be added in the future. The European space industry is invited to contribute to the Black Coatings BSDF Database by either providing a sample to be characterized or contribute with already measured BSDF data. The Black Coatings BSDF database will be a database created for and by the European space industry. Access to the database is free and can be requested by contacting the OOEL via: ooel@esa.int.

A Bidirectional Scattering Distribution Function (BSDF) describes how light from each incident direction is scattered (reflected and transmitted) by a simple or composite surface, such as a window shade. Compact, tabular BSDFs may be derived via interpolation, discretization and/or compression from goniophotometer measurements. These data-driven BSDFs can represent any measurable distribution to the limits of their tabulated resolution, making them more general than parametric or analytical BSDFs, which are restricted to a particular class of materials. However, tabulated BSDFs present a trade-off between higher sampling loads versus lower directional accuracy during simulation. Low-resolution BSDFs (e.g., Klems basis) may be adequate for calculating solar heat gains but fall short when applied to daylight glare predictions. The tensor-tree representation moderates this trade-off using a variable-resolution basis, providing detail where needed at an acceptable cost. Independently, a peak extraction algorithm isolates direct transmission from any tabular BSDF, enabling highresolution beam radiation and glare analysis through transmitting systems with a “vision” component. Our data-driven BSDF methods were validated with a pilot study of a fabric shade installed in an outdoor, full-scale office testbed. Comparisons between measurement and simulation were made for vertical illuminance, specular and near-specular transmission, and daylight glare probability. Models based on high resolution BSDF measurements yielded superior results when accounting for anisotropy compared to isotropic models. Models with higher resolution produced more accurate source luminance data than low-resolution models. Further validation work is needed to better characterize generality of observed trends from this pilot study., Building and Environment, 196, ISSN:0360-1323

Off-axis three-mirror anastigmat (TMA) telescopes provide excellent correction of aberrations over a large field-of-view in one direction. In a push broom configuration, this lightweight and compact optical configuration enables high-performing imaging. Moreover, passive multi-spectral acquisition can be achieved using a filter stack positioned at the detector vicinity. Stray light is a typical limiting factor for instrument performance and its control is specific to the type of optical configuration. We describe the stray light control and analysis methods in an off-axis TMA. The design intends to control first-order scattering from non-optical surfaces and to block straight shots. This is achieved through usage of elements such as apertures and baffles, both internal and external to the instrument. It will be demonstrated that the aperture stop is a critical element, whose stray light contribution can be controlled with V-groove vanes. Impact of mirrors roughness, a manufacturing physical limitation, is evaluated by modeling the bidirectional scattering distribution function and computing the stray light distribution at the detector for point-like source illumination. We show that the scattering on the different mirrors broaden differently the spot size, as the successive mirrors focus or expand the scattered rays differently. Finally, the ghost reflections inside the filter stack are evaluated and we show that there is no cross-talk between the different channels.

Deterministic illumination diffractive-diffusers have non-periodic short and medium scale topography. Because of the quasi-randomized locations and vertical sidewalls at phase transition boundaries, over-coating diffractive diffusers with thin film antireflection layers perturbs their function, resulting in illumination performance deviations and nonuniformities. To mitigate these effects, we added anti-reflection random nano-structures (rARSS) on the surface of three different classes of fused-silica multi-phase diffractive diffusers, using reactive-ion plasma etching. The diffusers were measured before and after the random nanostructure addition, using a polarized-laser scatterometer with a dynamic range of nine orders-of-magnitude. The bi-directional scatter distribution function (BSDF) was measured over the entire equatorial plane of incidence, to analyze the directionality of scattered light, and the impact of the rARSS on the optical performance of the diffusers. An overall Fresnel reflectivity suppression was measured in the directional illumination patterns, as well as, across the entire 180° angle-sweep. The designed deterministic illumination distribution patterns and contrast were unaffected by the presence of the rARSS.

Randomly nano-roughened interfaces between optical media can result in polarization-insensitive, angle-of-incidence independent, broadband anti-reflective (AR) performance. The on-axis AR effect correlates with the nano-roughness longitudinal scale (depth), whereas feature transverse dimension distributions (average feature diameters) cause selective scatter. Subwavelength, random AR structured surfaces (rARSS) can forward scatter light in the transmission direction, suppress specular Fresnel reflectivity, and enhance overall axial transmission throughput. In cases where the random nanoroughness average value approaches that of the incident radiation wavelength, the induced scatter can be detrimental to imaging applications due to uniformly distributing light from the specular into wider angles, reducing image contrast and broadening (blurring) the axial image spot. Using a polarized-laser scatterometer, we measured the bidirectional scattering distribution function (BSDF) of nano-roughened fused silica (FS) windows and compared them to an optical-quality FS flat and two different flat mirrors. The fabricated rARSS windows were optimized to have a broadband, anti-reflective specular response (R 400 nm). The BSDF was measured at 633-nm-wavelength, over the equatorial plane of the unit sphere, and at selected incidence angles below Brewster’s value. Granulometry of the roughened surfaces is correlated with the scattering data, for assessment of roughness-induced scattering effect. Using the BSDF data, single-surface and double-surface rARSS-treated windows were evaluated to determine any surface-to-surface scatter cascading effects.

Autonomous driving enable more use of in-vehicle interior lighting effects using advanced interior materials for illumination. Targeting premium visual ergonomics requires additional know how of today’s and future materials regarding light scattering. Within the presented work, we improved a goniophotometer towards a 2 standard deviation of < 0.08 %. This is in the range of a suitable limit so we successfully measured light scattering in terms of BSDF and/or BTDF of wood, transparent plastic (including 3D printed), and leather. These materials scatter light differently, so the results enable the base for optical simulation tools to design special visual effects.

This white paper summarizes the current state of the art in the field of measurement and simulation characterization of daylighting systems by bidirectional scattering distribution functions (BSDFs) and provides recommendations broken down by classes of systems and use cases.

Perforated Masonry Walls are traditional construction systems typical of the Mediterranean area, especially in existing rural buildings. Practical reasons are linked to their original employment as a separation element meant to be air permeable to promote cross-ventilation. Successively, they started to be designed for achieving architectural goals, integrating them with additional internal glazing. Moreover, due to their geometry, they can behave like real solar radiation shades, permitting daylight influx while controlling solar penetration. The implication of the use of these systems on daylighting and energy fields have not been widely analysed. This research intends to establish a starting point for their detailed daylighting analyses, considering them as Complex Fenestration Systems. To do so, brick materials were characterized through direct measurements of visual reflectance on a heterogeneous group of brick samples. Results show that reflectance values fall within the range of 0.081–0.262. Angle-dependent transmittances of seven masonry patterns were produced using Bidirectional Scattering Distribution Functions (BSDF) calculated with Radiance. For which, the highest reduction in visual transmittance values was found for solar incidence angles greater than 45°, reaching peaks approximately at 55–65°. These were tested and compared as shading systems on a test room with a South oriented glazed facade, located in Milan. Their implementation resulted in a mean indoor illuminance decay of ~15%. Lastly, the perforation ratio was confirmed not adequate to provide an insight into the visual performance of shading devices.