Mathematically modelling of radiative heat transfers requires to know the total emissivity of the surfaces. However, this factor is greatly dependent of a lot of parameters, for a given material its measure is hence necessary. The classical direct methods are not efficient at room temperature, the indirect methods are not accurate for great wavelength radiation (Huetz-Aubert 1990, Sacadura 1990).
The aim of this paper is to present a simultaneous measurement method of emissivity and reflectivity at room temperature.
The sample whose temperature is modulated is irradiated by an infrared source whose radiance is also modulated. Signal processing permit to extract from the noisy infrared flux the two relevant components which are proportional to the emissivity and the reflectivity of the studied surface. Three samples have been studied: an highly emissive paint (used as reference of emission), a highly reflective surface (used as reference of reflection) and a paint whose emissivity is intermediate. The sum of the aluminium paint emissivity and reflectivity is found to be equal to 1. Moreover this method does not require the knowledge a priori of the radiative properties of the two references.