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since the bidirectional reflectance distribution function applies to scattering media, it is inherently prone to speckle. Conditions to average out speckle by integration over solid angle both on the illumination side and on the detection side are analyzed.

LNE-Cnam has changed its traceability chain for measuring the spectral irradiance of a light source. This facility allows calibration of spectral irradiance of a standard lamp based on a comparison with a high temperature blackbody (HTBB). The reference spectral irradiance is determined by measuring the temperature of the HTBB with a filter radiometer calibrated against our radiant flux reference. This traceability scheme differs from the one used in our former setup, which was mainly based on the International Temperature Scale, ITS-90. Both principles are used in National Measurement Institutes. Our facility uses well known methods adapted to our best capabilities as well as a particular development in optical arrangement and filter radiometer calibration. Thanks to this new measurement setup, our spectral irradiance reference is now traceable to radiometric reference, i.e. our cryogenic radiometer. We have extended our measurement capability to cover the spectral range from 250 nm to 2500 nm. We have simplified the process by reducing the number of benches (three in one) and the number of operations, and we have designed a compact measuring setup through the use of a rotating integrative sphere. This allows us to reduce by at least a factor two our measurement uncertainties over almost the entire spectral range. With this new measurement facility, France participates in the ongoing CCPR k1.a key comparison. This is a key comparison of the Consultative Committee of Photometry and Radiometry for Spectral irradiance from 250 nm to 2500 nm of tungsten halogen lamps. This communication shows the method used, and its validation.

International audience; The Neolithisation of Europe involved socioeconomic and biological adaptations to new environments. The use of seaweed as livestock fodder, for example, was key to the introduction of animal husbandry to the Orkney archipelago, c. 3500 cal BC. Using stable isotope analysis of faunal remains from Skara Brae, this study provides new evidence for, and clarifies the chronology of, the adoption of seaweed consumption by sheep. The results show that sheep consumed moderate amounts of seaweed from the moment of their introduction to Orkney— a practice that facilitated the successful spread of the farming lifeways to the most remote areas of Europe.

11 pags., 11 figs., 3 tabs., app. -- OCIS codes: (290.1483) BSDF, BRDF, and BTDF; (120.1840) Densitometers, reflectometers; (120.5700) Reflection., The field of spectral radiance factor (SRF) measurements has seen growing interest in recent years. Scale conformity has so far only been established between the national metrology institutes (NMIs) of Germany and the USA. This study aims at a bigger, multilateral scale comparison. For this purpose, a total of six NMIs participated in a scale comparison of goniospectrophotometers based on neutral and colored diffusely reflecting ceramics samples. In addition, two universities, providing a home-built gonioreflectometer and two widely used commercially available color measurement instruments, respectively, were involved. The wavelength range of the scale comparison covers the visible wavelength range from 380 nm to 780 nm. Results indicate systematic issues and that the uncertainty evaluation of the NMIs requires further work; although for the greatest part of the covered spectral range the agreement is good., This work has been realized within the European Metrology Research Program (EMRP) project JRPIND52. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. We thank the European Commission and EURAMET e.V. for financial support.

In order to numerically quantify and to ensure consistency of the visual appearance of the end product, many industries perform color and gloss measurements, through the results of which they define maximum tolerances during quality control. For this, they may primarily rely on precision data for repeatability and reproducibility as reported by instrument manufacturers, who develop their instruments according to standardized measurement geometries defined in international standards. This paper reports on an investigation of the inter-instrument agreement between specular gloss meters which conform to universally adopted gloss standards. Six commercially available instruments, manufactured by three different companies, and twenty-five gloss artifacts, with specular gloss values ranging between 2 and 110 gloss units (60° geometry), were selected for use in the study. The repeatability and reproducibility of the instruments were assessed according to the criteria described in ASTM D523-14 and ISO 2813:2014, and to the specifications reported by the instrument manufacturers. Ray tracing simulations were performed by use of the bidirectional reflectance distribution function measurement data of two samples, and based on the standardized optical design of the specular gloss meter, in order to get a better insight on the expected tolerances of the gloss readings from a theoretical point of view. On average, the practical results indicate that both the repeatability and reproducibility values are higher than those specified in the recommendations and by the manufacturers. Ray tracing simulations confirm this finding. While specified repeatability and reproducibility thresholds are based on ideal standards, in practice, there are parameters that can lead to significant higher deviations. Care should therefore be taken when analyzing measurement results obtained from different instruments, and when defining tolerances for evaluation of gloss measurements.

International audience; The scattering of light by a surface is described by the bidirectional reflectance distribution function (BRDF). Unfortunately, this function cannot be straightforwardly acquired or modeled. French researchers have proposed interesting contributions to the field, with several models and accurate experimental systems. For instance, the National Metrological Institute (LNE-CNAM) has implemented the best angular resolution goniospectrophotometer (0.015°). Modeling the BRDF has also been deeply studied in France, especially with the microfacet theory in recent years, a better understanding of the shadowing–masking function, new general distribution functions, visible normals, interfaced Lambertian microfacets, and analysis concerning light multiple reflections. This paper presents the state of the art regarding some significant French contributions in these fields.

The most straightforward way to assess the glossiness of a surface is by measuring the specular reflectance by use of a specular glossmeter. Although alternative measurement methods have been proposed, this is still the most frequently used instrumental measurement technique for gloss evaluation until today. However, due to both the multidimensional nature of gloss perception and to the initial purpose of a specular glossmeter only to judge the gloss differences of surfaces with similar appearance, specular glossmeter results do not seem to provide a reliable basis for estimating the gloss appearance of a surface. During the past decades, increased attention has been paid to understanding how the human visual system arrives at a particular sensation of surface gloss, and which factors influence this process. This article was established in response to these new insights, and provides the reader an overview of the most important developments and findings regarding gloss measurement and gloss perception over the past 15 years. With the ultimate goal to achieve a better correspondence between gloss measurement and gloss perception in the future, issues of alternative measurement methods are considered, and some suggestions for relevant future research are proposed. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 559–570, 2014

Intra-tooth sequential analysis of enamel δ18O is currently used to investigate birth seasonality in past animal populations, offering new insights into seasonal availability of animal resources, herd management and seasonality of site occupation. Reference data sets are still required to address two major difficulties: (1) that inter-individual variability in the record of the seasonal cycle is affected by tooth size; and (2) that the season of birth cannot be directly estimated from the timing of tooth growth, because of a delay in enamel mineralization. We present a data set acquired on the lower second molar of 10 modern sheep from Rousay (Orkney) born within a few weeks of each other in April/May and submitted to the same environmental conditions until death. All sheep have recorded a sinusoidal pattern of δ18O variation spanning approximately a year. From the difference between the expected and the measured time sequence, the delay of enamel mineralization is estimated to be 5–6 months. The data set is then described using a model mainly based on a cosine function. The period, corresponding to the length of the M2 crown formed over a year, averaged 35.8 mm. A very slight variation of tooth growth rate with time and no attenuation of the isotopic signal towards the cervical margin of the crown could be detected in this data set. The lowest δ18O values, corresponding to the sheep's first winter, were tracked at a distance from the enamel/root junction that varied between 23.0 and 30.3 mm (xmin mean = 27.6 mm); the highest δ18O values, corresponding to the sheep's second summer, were between 6.3 and 11.6 mm (xmax mean = 9.9 mm). Most of the variability can be attributed to tooth size. When normalized on the period, xmin and xmax are 0.28 (± 0.05) and 0.78 (± 0.05) on average, meaning that the Rousay sheep have recorded the minimum and maximum δ18O values on average at 78% and 28%, respectively, of the end of the periodic cycle recorded in the second molar.

The Laboratoire National de Métrologie et d'Essais, LNE-CNAM (France) and The National Institute of Metrology, RCM LIPI (Indonesia) agreed in December 2013 to conduct a bilateral comparison on luminous flux using a group of lamps as transfer standards. The aims of the comparison were: • To link the RCM LIPI realized lumen to the CCPR K4 reference value • To demonstrate the RCM LIPI capability in calibrating tungsten standards lamps. The comparison and its protocol were approved by the CCPR and registered with KCDB with the comparison number: EURAMET.PR-K4.2. KEY WORDS FOR SEARCH Luminous flux, PR K4, Bilateral Comparison Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

International audience; Leaf reflectance of monocotyledons generally displays a strong azimuthal anisotropy due to the longitudinal orientation of the veins. The Cook and Torrance (CT) bidirectional reflectance distribution function model was adapted to account for this distinctive feature. The resulting ACT (Anisotropic Cook and Torrance) model is based on the decomposition of the roughness parameter into two perpendicular components. It is evaluated on sorghum (Sorghum halepense) and wheat (Triticum durum) leaf BRF (Bidirectional Reflectance Factor) measurements acquired using a conoscope system. Results show that the ACT model fits the measurements better than azimuthally isotropic surface models: the root mean square error computed over all the BRF measurements for both leaves decreases from ≈0.06 for the Lambertian model to ≈0.04 for the CT model and down to ≈0.03 for the ACT model. The adjusted value of the refraction index is plausible (n ≈ 1.32) for both leaves while the retrieved roughness values perpendicular to the veins (sorghum = 0.56; wheat = 0.46) is about two times larger than that parallel to the veins (sorghum = 0.27; wheat = 0.18). Nonetheless, the observed residual discrepancies between the ACT model simulations and the measurements may be explained mainly by the Lambertian assumption of the volume scattering.

The EUROMET project 823, "Comparison of luminous intensity and luminous flux using lamps as transfer standards" between LNE (formerly BNM), France, and INM-RO, Romania, has linked the INM-RO real-ized candela to the CCPR key comparison reference values. The comparison was registered on BIPM key comparison data base with the numbers EUROMET.PR-K3.a.1. The comparison has been piloted by LNE. It has been carried out by successive calibrations of a group of four travelling standard lamps in the two laboratories. The lamps were first calibrated by INM-RO, then cal-ibrated by LNE and calibrated by INM-RO in order to check for any drift or instability. The measurements have been performed over the period November 2004 to June 2006. According to the results of the comparison, the Degree of Equivalence of the candela realized by INM-RO to the Key Comparison Reference Value of CCPR-K3 is - 0,72 % with an expended uncertainty (k = 2) of 2.14 %. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

We see objects because they reflect light. This reflected light contains information that allows us not only identify the shape of the object but also its appearance. The overall appearance of an object is a combination of different visual attributes like gloss, texture, color or transparency, which are produced by the interaction between the object, the light falling upon it and the visual system [1].Our interest in this article is to characterize the gloss of a surface. Our approach is the measurement of the Bidirectional Reflectance Distribution Function (BRDF) of the surface in, and around the specular direction, where the specular peak is located. For this, we developed a dedicated gonioreflectometer with a very high angular resolution. In this paper we present the equipment and measurements made on different surfaces

The bidirectional reflectance distribution function (BRDF) represents the evolution of the reflectance with the directions of incidence and observation. Today BRDF measurements are increasingly applied and have become important to the study of the appearance of surfaces. The representation and the analysis of BRDF data are discussed, and the distortions caused by the traditional representation of the BRDF in a Fourier plane are pointed out and illustrated for two theoretical cases: an isotropic surface and a brushed surface. These considerations will help characterize either the specular peak width of an isotropic rough surface or the main directions of the light scattered by an anisotropic rough surface without misinterpretations. Finally, what is believed to be a new space is suggested for the representation of the BRDF, which avoids the geometrical deformations and in numerous cases is more convenient for BRDF analysis.

Coatings can be classified by either their appearance, such as glitter, or by their function, such as corrosion protection. However, pigments are currently being manufactured with new and unique appearance attributes that can not be characterized by traditional methods. These coatings may exhibit differences in their perceived color with changes in the illumination or viewing angle, or both. Properties such as these have become rudimentary in the production of currency, cosmetics, and retroreflective materials. The primary impetus of goniospectrometry at NIST is to develop accurate measurement protocols for reproduction and quality control of appearance attributes, such as color matching, by determining the minimum set of illumination and viewing geometries needed to accurately characterize the perceived color. Here, we present a new goniospectrometer developed at NIST that allows the measurement of the complete bi-directional reflectance distribution function (BRDF) for colored surfaces with the objective of differentiating between the scattering mechanisms in the coating. The illumination is provided by a monochromator with a spectral resolution of 0.05 nm between 360 nm and 780 nm. The sample can be moved about 3 different axes, allowing illumination and viewing for any direction within the hemisphere about the sample, including grazing angles, with accuracy better than 0.01° for each axis. This equipment will become the future provider of standard BRDF measurements at NIST, for the characterization of complex surfaces like gonioapparent coatings or retroflective surfaces.

Gloss is an attribute of visual appearance that originates from the geometrical distribution of the light reflected by the surface. We used the maximum likelihood difference scaling (MLDS) procedure (L.T. Maloney & J. N. Yang, 2003) to estimate gloss scales over an extended range. Observers' judgments were obtained for a series of 10 black, coated samples for two directions of illumination, in binocular and monocular vision. The results showed a nonlinear relation between gloss percept and instrumental specular gloss values. Sensitivity is higher at extreme scale values than in the middle. In binocular vision, the sensitivity to gloss is higher than in monocular vision exclusively for high gloss levels. Lastly, we found that gloss difference scales, when expressed in terms of the samples rather than the photometric characteristics, vary little with the direction of illumination. Gloss scaling thus seems to be independent of the geometrical variations of the luminous flux at the surface of the sample. By analogy with the term "color constancy," we call this property "gloss constancy."

The EUROMET-PR-K6 key comparison on spectral regular transmittance was carried out in the framework of the Mutual Recognition Arrangement by 17 laboratories: BEV (Austria), CMI (Czech Republic), GUM (Poland), IFA (Spain), INM (Romania), INRIM (Italy), IPQ (Portugal), LNE?INM (France), METAS (Switzerland), MKEH (Hungary), MIKES (Finland), NPL (United Kingdom), PTB (Germany), SMU (Slovakia), SP (Sweden), UME (Turkey), VSL (The Netherlands), with the LNE?INM acting as the central and reporting laboratory. The link to CCPR-K6 is ensured by six link laboratories (IFA, LNE?INM, MIKES, NPL, PTB, SMU) The aim of the comparison was restricted to checking the accuracy of the radiometric scale of spectrophotometers, using coloured glass filters with nominal transmittance of approximately 92%, 56%, 10%, 1% and 0.1%. The wavelengths of measurement were 380 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm and 1000 nm. The comparison was a star type comparison with the samples provided by the pilot laboratory and sent out to all the participants at the same time. The report describes in detail the measurements made at the LNE?INM and summarizes the reports submitted by the participants. The comparison of the results of measurements carried out by the pilot laboratory before and after the circulation of the filters points out that the stability of most of the filters was rather poor. Moreover, for the coloured glass filters (filters B to E), the drift was wavelength dependent. As a consequence, for many results, the uncertainty due to the drift of the filters during the comparison is the major cause of uncertainties, much larger than the measurement uncertainty of the measurements reported by the laboratories. Measurement results from participants and their associated uncertainties were analysed in this report according to the Guidelines for CCPR Comparison Report Preparation but with some adjustment for taking into account that transmittance measurements have unit 1. Across the spectral region (380 nm to 1000 nm) there were eight wavelengths at which a comparison was made. These were treated entirely independently and thus the report describes eight comparisons for each type of filter. The linkage of this RMO key comparison to the CCPR-K6 key comparison takes a particularly simple form because (a) the pilot laboratory was also the pilot laboratory for the CCPR-K6 comparison and (b) the five other laboratories serving as links between the two contributed the same measurements on the same artefacts in each comparison. It follows from (a) and (b) that the same result is obtained by linking through any one of these five laboratories or any combination of them. The degrees of equivalence of participants in this RMO key comparison have hence been evaluated by linking through values measured by the pilot laboratory. Because the CCPR KCRV is defined relative to the values obtained by the pilot laboratory and the ?X,i (the difference between participant measurement and the pilot laboratory measurement) are also defined relative to measurements by the same pilot laboratory, the unilateral degree of equivalence Di of the national metrological institute i takes the simple form: Di = ?i ? ?KCRV Ui = k[u2(?i) + u2(?KCRV)]1/2; ? ? ? ?k = 2. All the results and a graphical representation of the unilateral degrees of equivalence with k = 2 are proposed in the final report. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

The EURAMET-PR-K6.1 is a bilateral key comparison on spectral regular transmittance carried out in the framework of the Mutual Recognition Arrangement between the LNE-INM/CNAM (France) and the DMDM (Republic of Serbia). The LNE-INM/CNAM acted as the pilot laboratory and provided the link to the key comparison CCPR-K6. The aim of the comparison was restricted to checking the accuracy of the radiometric scale of spectrophotometers, using coloured glass filters with nominal transmittance of approximately 92%, 56%, 10%, 1% and 0.1%. The wavelengths of measurement were 380 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm and 1000 nm. The report describes in detail the facilities of the two participants for spectrophotometric measurements and the uncertainty budgets are presented. The comparison of the results of measurements carried out by the pilot laboratory before and after the circulation of the filters points out that the instability of the filters was not negligible. Moreover, for the coloured glass filters (filters B to D), the drift was wavelength-dependent. As a consequence, the drift of the filters during the comparison has been included in the calculation of the total uncertainty. Measurement results and their associated uncertainties were analysed in this report according to the Guidelines for CCPR Comparison Report Preparation but with some adjustment for taking into account that transmittance measurement have unit 1. Across the spectral region (380 nm to 1000 nm) there were eight wavelengths at which a comparison was made. These were treated entirely independently and thus the report describes eight comparisons for each type of filter. The linkage of this bilateral key comparison to the CCPR-K6 key comparison takes a particularly simple form because the pilot laboratory was also the pilot laboratory for the CCPR-K6 comparison, and the artefacts used were the same as those of CCPR-K6. The degrees of equivalence of DMDM have hence been evaluated by linking through values measured by the pilot laboratory. All the results and graphical representations of the unilateral degrees of equivalence with k = 2 are proposed in the final report. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

The CCPR K6 key comparison on spectral regular transmittance was carried out in the framework of the CIPM Mutual Recognition Arrangement by 15 laboratories: IFA (Spain), KRISS (Republic of Korea), LNE-IMN (France), NIST (USA), NMC-A*STAR (Singapore), NMi (The Netherlands), NMIA (Australia), NMIJ/AIST (Japan), NPL (United Kingdom), NRC (Canada), MIKES (Finland), MSL (New Zealand), PTB (Germany), SMU (Slovakia) and VNIIOFI (Russia), with the LNE-INM acting as the central and reporting laboratory. The aim of the comparison was restricted to checking the accuracy of the radiometric scale of spectrophotometers, using coloured glass filters with nominal transmittance of approximately 92%, 56%, 10%, 1% and 0.1%. The wavelengths of measurement were 380 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm and 1000 nm. The comparison was a star type comparison with the samples provided by the pilot laboratory and sent out to all the participants at the same time. The report describes in detail the measurements made at the LNE-INM and summarizes the reports submitted by the participants. The comparison of the results of measurements carried out by the pilot laboratory before and after the circulation of the filters points out that the stability of most of the filters was rather poor. Moreover, for the coloured glass filters B to E, the drift was wavelength dependent. As a consequence, for many results, the uncertainty due to the drift of the filters during the comparison is the major cause of uncertainties, much larger than the measurement uncertainty of the measurements reported by the laboratories. Measurement results from participants and their associated uncertainties were analysed in this report according to the Guidelines for CCPR Comparison Report Preparation, but with some adjustment for taking into account that transmittance measurements have unit 1. Across the spectral region (380 nm to 1000 nm) there were 8 wavelengths at which a comparison was made. These were treated entirely independently and thus the report describes 8 comparisons for each type of filter. The key comparison reference values of the comparison and the degrees of equivalence of the participants are based on weighted means with cut-off and the removal of very few values (4 values out of 600) considered as outliers. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).