The average reflectance will evaluate for wavelength between 230 and 700nm. The absorptivity (α) will obtain by using the equation:

α + R +T =1

Where α is the absorptivity, R is the reflectance, and t is the transmittance of the surface. Since T =0 for opaque surfaces, then α =1-R.

        For emissivity measurements, the infrared (IR) spectrometer will be used. The emissivity (ԑ) given by (1- reflectance) will calculated from the reflectance measurements in the IR range ( from 2500 to 25000nm).

Dear Khater,

welcome you can measure then using pyranometer as a black body abosrber.

Best wishes

http://sustech.edu/staff_publications/20150325081551137.pdf