Determination of hemispherical emittance by measurements of infraredbi-hemispherical reflectance

Abstract

Abstract : A technique for the experimental determination of spectral, hemispherical emittance of surfaces in the infrared wavelength region is suggested. The technique consists of using an infrared integrating sphere to measure spectral, bi-hemispherical reflectance. The feasibility of the technique is justified both on an analytical basis and, to the extent possible, on an experimental basis. A spectral, bi-hemispherical reflectometer is described. The device produces reflectance measurements with an estimated uncertainty of plus or minus 2 per cent of full scale at 5 microns. Due to detector noise the estimated uncertainty increases to plus or minus 10 per cent of full scale at 16 microns. Reflectometer measurements of the spectral hemispherical emittance of fused quartz in the 5 to 16 micron range are presented to illustrate operation of the reflectometer. It is concluded that the device has high potential as an analytical instrument and that developmental efforts should be directed toward extending its wavelength range.