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Measuring Spatially- and Directionally-varying Light Scattering from Biological Material
Published on: May 20, 2013
Systematic errors in the measurement of emissivity caused by directional effects
Abraham Kribus1, Irna Vishnevetsky, Eyal Rotenberg
1Department of Fluid Mechanics and Heat Transfer, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel. kribus@eng.tau.ac.il
Abstract:
Accurate knowledge of surface emissivity is essential for applications in remote sensing (remote temperature measurement), radiative transport, and modeling of environmental energy balances. Direct measurements of surface emissivity are difficult when there is considerable background radiation at the same wavelength as the emitted radiation. This occurs, for example, when objects at temperatures near room temperature are measured in a terrestrial environment by use ofthe infrared 8-14-microm band.This problem is usually treated by assumption of a perfectly diffuse surface or of diffuse background radiation. However, real surfaces and actual background radiation are not diffuse; therefore there will be a systematic measurement error. It is demonstrated that, in some cases, the deviations from a diffuse behavior lead to large errors in the measured emissivity. Past measurements made with simplifying assumptions should therefore be reevaluated and corrected. Recommendations are presented for improving experimental procedures in emissivity measurement.
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