Measurement, reporting and applications of bidirectional reflectance distribution function

The thesis addresses the issues of measurement, reporting and applications of bidirectional reflectance distribution function (BRDF) from the point of view of modern problems and corresponding solutions. The first part of the work considers the development of the new 3D gonioreflectometer aimed to overcome the limits of Aalto University's existing instrument by enabling out-of-plane SI-traceable BRDF measurements and allowing horizontal sample alignment needed to study reflective properties of loose samples like soil or sand. The operation principles of the new instrument as well as the design of its illumination, detection and goniometer systems are described. The uncertainty budget of the instrument is thoroughly studied and concluded in a table with numerical values assigned to different uncertainty components. The performance of the new gonioreflectometer is validated by test measurements compared with in-plane BRDF determined by Aalto University's absolute reference gonioreflectometer. The second part focuses on reporting of BRDF data and proposes a solution for BRDF data non-conformity and compatibility problems in the form of thoroughly documented universal Findable, Accessible, Interoperable and Reusable (FAIR) BRDF file format. The file format based on JavaScript Object Notation (JSON) syntaxis is carefully documented and supported by JSON schema that enables its automated validation. The uptake of the presented BRDF data format is facilitated by introduction of an open-source software build around it. The software serves as an interface between the user and JSON schema validator as well as allows to visualize and compare BRDF data stored in files. The third part considers application of BRDF for material characterization. The developed new gonioreflectometer is used to characterize BRDF of the loose ground sample collected from RadCalNet Gobabeb test site used for vicarious sensor calibration of Earth observation satellites. The peculiarities of the ground sample as well as its preparation procedures are explained. A data synthesis method for combination of BRDF data of various ground sample fractions is introduced. The results on Gobabeb ground sample BRDF from laboratory characterizations are presented, analysed and compared with in-situ measurements. The last part of the thesis demonstrates the application of BRDF for functional material design. It introduces a new method to develop reflectance reference samples with the BRDF similar to the BRDF of crumpled reflective insulation material samples. The method based on microfacet model is thoroughly described and tested using physics-based Monte-Carlo simulations. Test results as well as example designs for anisotropic and isotropic reflectance reference samples for aluminium foil are presented, explained and discussed