Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica

The surface reflection of solar radiation comprises an important boundary condition for solar radiative transfer simulations. In polar regions above snow surfaces, the surface reflection is particularly anisotropic due to low Sun elevations and the highly anisotropic scattering phase function of the snow crystals. The characterization of this surface reflection anisotropy is essential for satellite remote sensing over both the Arctic and Antarctica. To quantify the angular snow reflection properties, the hemispherical-directional reflectance factor (HDRF) of snow surfaces was derived from airborne measurements in Antarctica during austral summer in 2013/14. For this purpose, a digital 180∘ fish-eye camera (green channel, 490–585 nm wavelength band) was used. The HDRF was measured for different surface roughness conditions, optical-equivalent snow grain sizes, and solar zenith angles. The airborne observations covered an area of around 1000 km × 1000 km in the vicinity of Kohnen Station (75∘0′ S, 0∘4′ E) at the outer part of the East Antarctic Plateau. The observations include regions with higher (coastal areas) and lower (inner Antarctica) precipitation amounts and frequencies. The digital camera provided upward, angular-dependent radiance measurements from the lower hemisphere. The comparison of the measured HDRF derived for smooth and rough snow surfaces (sastrugi) showed significant differences, which are superimposed on the diurnal cycle. By inverting a semi-empirical kernel-driven bidirectional reflectance distribution function (BRDF) model, the measured HDRF of snow surfaces was parameterized as a function of solar zenith angle, surface roughness, and optical-equivalent snow grain size. This allows a direct comparison of the HDRF measurements with the BRDF derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite product MCD43. For the analyzed cases, MODIS observations (545–565 nm wavelength band) generally underestimated the anisotropy of the surface reflection. The largest deviations were found for the volumetric model weight fvol (average underestimation by a factor of 10). These deviations are likely linked to short-term changes in snow properties

Colour and Colorimetry Multidisciplinary Contributions Vol. XIb

It is well known that the subject of colour has an impact on a range of disciplines. Colour has been studied in depth for many centuries, and as well as contributing to theoretical and scientific knowledge, there have been significant developments in applied colour research, which has many implications for the wider socio-economic community. At the 7th Convention of Colorimetry in Parma, on the 1st October 2004, as an evolution of the previous SIOF Group of Colorimetry and Reflectoscopy founded in 1995, the "Gruppo del Colore" was established. The objective was to encourage multi and interdisciplinary collaboration and networking between people in Italy that addresses problems and issues on colour and illumination from a professional, cultural and scientific point of view. On the 16th of September 2011 in Rome, in occasion of the VII Color Conference, the members assembly decided to vote for the autonomy of the group. The autonomy of the Association has been achieved in early 2012. These are the proceedings of the English sessions of the XI Conferenza del Colore

Energy Efficient Lighting in Plant Factories: Addressing Utilance

Vertical farming is considered to play a crucial role in future food supply. Until today, the high amount of electrical energy required for artificial lighting has been problematic in this context. Various possibilities for increasing efficiency through adapted lighting conditions have been and are being investigated. However, comparably little attention is paid to increasing utilance, i.e., the amount of photons that can effectively be used by the plant. In this work, a novel targeted lighting strategy is therefore proposed that allows for a dynamic adaptation of the luminaires’ light distribution to match the effective crop size at each stage of plant growth in a fully-automated manner. It is shown that the resulting utilance can significantly be increased compared to standard full-coverage lighting. Moreover, it is found that the proposed strategy is likely to consume less than half of the electrical energy usually required for the latter. An additional increase in system efficiency can be prognosticated and the potential energy savings are estimated based on assumptions of future LED generations derived from literature

Design of a time-efficient video-goniophotometer combining bidirectional functions assessment for transmission and reflection

A detailed knowledge of the light distribution characteristics through advanced window systems is required to improve the visual comfort of the building's occupants while controlling the propagation of daylight in rooms and the solar gains. An innovative bidirectional goniophotometer has recently been set up for this purpose, using digital image capture and the projection of the emerging light on a diffusing screen. It therefore provides a continuous investigation of the bidirectional transmission figures in a time-efficient way. This instrument was converted into a double-purpose device, allowing both transmission and reflection measurements, which induced several strong constraints due to the conflict of incident and emerging light flux in reflection mode: on one hand the incident beam had to be restricted to the sample area only; on the other hand, as the screen obstructed the incoming light flux in some positions, a special opening in the latter was required. The practical answer to these constraints, detailed in this paper, proved to be reliable, appropriate and efficient. (c) 2004 Elsevier B.V. All rights reserved

Appearance synthesis of fluorescent objects with mutual illumination effects

We propose an approach for the appearance synthesis of objects with matte surfaces made of arbitrary fluorescent materials, accounting for mutual illumination. We solve the problem of rendering realistic scene appearances of objects placed close to each other under different conditions of uniform illumination, viewing direction, and shape, relying on standard physically based rendering and knowledge of the three-dimensional shape and bispectral data of scene objects. The appearance synthesis model suggests that the overall appearance is decomposed into five components, each of which is expanded into a multiplication of spectral functions and shading terms. We show that only two shading terms are required, related to (a) diffuse reflection by direct illumination and (b) interreflection between two matte surfaces. The Mitsuba renderer is used to estimate the reflection components based on the underlying Monte Carlo simulation. The spectral computation of the fluorescent component is performed over a broad wavelength range, including ultraviolet and visible wavelengths. We also address a method for compensating for the difference between the simulated and real images. Experiments were performed to demonstrate the effectiveness of the proposed appearance synthesis approach. The accuracy of the proposed approach was experimentally confirmed using objects with different shapes and fluorescence in the presence of complex mutual illumination effects

On advanced daylighting simulations and integrated performance assessment of complex fenestration systems for sunny climates

The inclusion of daylight in buildings represents several benefits: its use not only signifies a reduction in the building energy consumption through the compensation of electric lighting, it also has positive effects in the execution of human activities. Through its spectral composition, it contributes to create a better interior atmosphere for visual comfort, leading to a better performance on working tasks. It also influences biological human cycles, which has an impact on human alertness, mood and well-being. Compared with electric light, its intensity and dynamic variations have a stimulating effect by providing a connection with the exterior environment. However, for buildings located at low latitudes (between 23°N and S), the inclusion of daylight implies the admission of sunrays, which affect the visual comfort and perception of the indoor environment by altering the interior luminance distribution increasing the risk of glare. An additional unfavourable effect is the increment of the interior thermal loads which represent a risk of overheating for the occupants. In those regions, common practices such as: the reduction of the window size, the use of tinted glazing and solar protection are usually applied to buildings in the search of overcoming such problems. However, the use of such strategies also implies a reduction of the admission of daylight inducing the use of electric light, which is incongruent in countries with large amounts of this natural resource. The use of Complex Fenestration Systems (CFS) may represent a solution given their characteristics: daylight redirection and direct solar rays protection. The latter would contribute to control the admission of solar gains while maintaining a good visual interior environment. However, the appropriate selection of CFS requires a careful evaluation of their features and performance regarding their suitability to the building location. This thesis explores the potentiality of using CFS to improve the interior daylight distribution in buildings located at low latitudes while maintaining a satisfactory visual and thermal interior environment for the occupants. In order to do this, the existing daylight situation of two office rooms located in the central-north of México (Zacatecas 22° 783' N., 102° 583' W, Altitude: 2543m) were monitored from 2011 to 2013. Illuminance and luminance were measured on periods of the year that are crucial for the interior luminous environment (summer and winter solstices together with spring equinox), in order to characterize the existing daylighting situation and to study the dispersion of results obtained using a virtual model which reproduces the features of both offices. The performance of five CFS was then tested using computer simulations in order to assess their suitability to the local sky conditions. For this, three main factors were taken into account: the improvement of the interior daylight distribution, the risk of glare and overheating. The effects of the CFS in a room regarding such conditions were simulated using RADIANCE and Energy Plus using BTDF data (Bidirectional Transmission Distribution Function that characterizes the CFS’s lighting transmission properties) assessed by the use of a gonio-photometer. The assessment was performed first during the winter and summer solstices as well as spring equinox and secondly then on annual basis. The latter was done in order to take into account the daylight variation characteristics of two locations with prevailing clear sky conditions. The results obtained allow determining the CFS that better contributes to a better interior luminous environment in each building without compromising the thermal and visual comfort of the occupants

Modèles spectraux pour les surfaces imprimées : approches directes et problématiques inverses

Ce mémoire cherche à décrire et mettre en perspective une démarche scientifique construite durant une dizaine d’années de recherches dans le domaine de la reproduction des couleurs, un domaine associé aux disciplines de l’optique et des sciences de l’image. Les travaux présentés visent prédire le rendu visuel de surfaces traitées par divers procédés de coloration, et de créer des effets visuels nouveaux pour les arts graphiques à des fins esthétiques ou de sécurisation de documents. Les connaissances produites portent sur le développement de modèles optiques originaux décrivant la propagation de la lumière dans les couches colorantes et les supports, la métrologie optique nécessaire à la caractérisation de ces surfaces ou à la calibration des modèles, la conception d’effets visuels par impression grâce aux modèles inverses. Le travail de modélisation forme la partie amont de ces recherches. La caractérisation des surfaces et la conception d’effets visuels innovants font l’objet de collaborations industrielles avec des grandes ou petites. Les principaux résultats portent sur des configurations originales d’impression où plusieurs images en demi-tons sont vues l’une au travers de l’autre : impressions recto-verso, empilements d’imprimés… Des modèles propres à ces configurations ont été développés et des effets visuels, quasiment impossibles à obtenir sans modèle, ont été conçus. Une autre activité plus récente concerne de nouveaux procédés de marquage en couleur par laser sur des surfaces pré-fonctionnalisées. Par ailleurs, s’esquisse une démarche plus fondamentale sur l’interaction entre la lumière et les matériaux d’impression et sur la métrologie optique de surfaces à apparence variable

A review of thermal and optical characterisation of complex window systems and their building performance prediction

Window systems play a key role in establishing both the thermal and luminous environments within buildings, as well as the consequent energy required to maintain these for the comfort of their occupants. Various strategies have been employed to improve the thermal and optical performance of window systems. Some of these approaches result in products with relatively complex structures. Thus, it becomes difficult to characterise their optical and thermal properties for use in building performance prediction. This review discusses the experimental and numerical methods used to predict the thermal and optical behaviour of complex window systems. Following a discussion of thermal characterisation methods available in the literature that include experimental test methods, theoretical calculation methods and Computational Fluid Dynamic methods, sophisticated optical methods, such as use of Bidirectional Scatter Distribution Functions (BSDF) to optically characterise complex window systems, are introduced. The application of BSDF allows advanced daylight assessment metrics along with daylight evaluation tools to be used to realise dynamic annual prediction of the luminous environment. Finally, this paper reviews methods that permit the prediction of the combined thermal, daylight and energy behaviour of buildings that make use of complex window systems