Investigations and Applications of Angle-Resolved Measurements of Spectral Reflectance and Transmittance
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School of Electrical Engineering |
Doctoral thesis (article-based)
| Defence date: 2024-07-03
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Authors
Date
2024
Major/Subject
Mcode
Degree programme
Language
en
Pages
69 + app. 67
Series
Aalto University publication series DOCTORAL THESES, 128/2024
Abstract
This doctoral thesis explores the quantification of a material's appearance through angle-resolved measurements of spectral reflectance and transmittance. The appearance of a material often determines the quality of a product across various sectors of industry, entertainment, and research. Therefore, there is a need for accurately characterized reference standards, traceable to the international system of units (SI). Accordingly, this thesis focuses on bidirectional reflectance distribution function (BRDF) and bidirectional transmittance distribution function (BTDF) measurements of diffuse material in the visible and near-infrared wavelength range. Moreover, the thesis presents the development of an SI-traceable facility for the accurate determination of angle-resolved scattering quantities. One application of BRDF includes the verification of proper operation of ray tracing models (RTM) using calibrated reference standards. The first part of the thesis introduces an SI-traceable 3D gonioreflectometer for BRDF measurements of an artificial sample. To find a suitable sample for the verification process, the 3D instrument systematically measured several material candidates, evaluating their BRDF characteristics. Subsequently, the instrument's uncertainty in BRDF measurements is characterized, and the reliability of RTM is checked by comparing simulated and measured BRDF data of an artificial sample based on the best material candidate. The following sections of the thesis are dedicated to exploring the practical applications of BTDF. The sections present the development of a facility for SI-traceable BTDF measurements, featuring an absolute gonioreflectometer extended to BTDF measurements in the visible and near-infrared wavelength range. The instrument specializes in measurements of matte surfaces that uniformly transmit light in all directions. Validation of the absolute instrument's capabilities in BTDF measurements was conducted through a detailed uncertainty evaluation and also a comparison measurement with a commercial spectrophotometer. Furthermore, the thesis discusses the adaptation of the 3D instrument for out-of-plane measurements of BTDF, recognizing the utility of materials that have anisotropic scattering distributions. The fourth part of the thesis offers considerations on the definition of BTDF in the context of thick sample measurement. The thesis presents a method for correcting measured BTDF as a function of viewing zenith angle based on the geometry of the facility. Furthermore, the method was validated by using two instruments exhibiting varying degrees of sensitivity to sample thickness. This work provides tools for unambiguous treatment of the BTDF of thick samples.Description
Supervising professor
Ikonen, Erkki, Prof., Aalto University, Department of Electrical Engineering and Automation, FinlandThesis advisor
Manoocheri, Farshid, PhD, Aalto University, Department of Information and Communications Engineering, FinlandKeywords
appearance, BRDF, BTDF, SI-traceable, gonioreflectometer, ray tracing model, near-infrared, angle-resolved reflectance, angle-resolved transmittance
Other note
Parts
- [Publication 1]: V. Leroy, R. Aschan, P. Woolliams, S. Schunke, F. Manoocheri, and Y. Govaerts, “An SItraceable protocol for the validation of radiative transfer model-based reflectance simulation”. Submitted for publication in 2024
- [Publication 2]: R. Aschan, D. Lanevski, F. Manoocheri and E. Ikonen,” Measurement of bidirectional transmittance distribution function in the visible and near-infrared spectral range”. Submitted for publication in 2024
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[Publication 3]: J. Fu, T. Quast, E. Velke, M. Esslinger, M. Pastuschek, A. Schirmacher, R. Aschan, F. Manoocheri and E. Ikonen, "Development of primary reference facilities and measurement comparison of standard artifacts for the bidirectional transmittance distribution function," Review of Scientific Instruments, vol. 94, no. 8, 083102, 2023.
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202308305292DOI: 10.1063/5.0151803 View at publisher
- [Publication 4]: R. Aschan, F. Manoocheri and E. Ikonen,” Considerations on measurement of bidirectional transmittance distribution function of thick samples over a wide range of viewing zenith angles,” Measurement Science and Technology, Accepted for publication, 2024