Experimental validation of the diffusion function model for accuracy-enhanced thermoreflectometry

Benjamin Javaudin (1) , Rémi Gilblas (1) , Thierry Sentenac (1) , Yannick Le Maoult (1)

1 ICA - Institut Clément Ader

In thefield of thermography, the main problem in measuring truetemperature lies in determining the emissivity. Thermoreflectometryovercomes this problem by an in-situ emissivity determinationmethod based on bidirectional reflectivity measurement. Thismethod introduces a diffusion function model which links the bidir-ectional reflectivity measured to the emissivity. The true temperatureand the model parameters are then found with the solution ofa system of radiometric equations. Thefirst contribution of this articleis the modelling of the diffusion function using physical models ofthe Bidirectional Reflectivity Distribution Function (BRDF). The sug-gested model depends on two parameters: the roughness and thegeometrical setting of the measurement. For a given configuration,the identification of the roughness parameter provides a knowledgeof the evolution of the surface state according to the operatingconditions of the material (deformation, damage, etc.). The secondcontribution is the validation of the roughness parameter identifiedby the thermoreflectometry method. Validation is done ona reference sample in platinum with a measured roughness.Another validation is performed on the BRDF model by measure-ments on a Fourier transform spectrometer. It validates the shape ofthe model and gives a second validation of the roughness parameterby using curve-fitting identification.

Mots clés: BRDF; modelling; thermoreflectometry; emissivity; activethermography; active thermography

Domaines: Sciences de l'ingénieur [physics]

Benjamin Javaudin, Rémi Gilblas, Thierry Sentenac, Yannick Le Maoult. Experimental validation of the diffusion function model for accuracy-enhanced thermoreflectometry. Quantitative InfraRed Thermography Journal, 2021, 18 (1), pp.18-33. ⟨10.1080/17686733.2019.1665297⟩. ⟨hal-02384426⟩