Partial Coherence and Practical Radiometry

Abstract

A review is presented of recent claims on the effects of partial coherence in radiometric measurements, particularly in relation to spectral irradiance intercomparisons. It is shown that for practical sources typically used in radiometric laboratories, effects claimed to be due to partial coherence are equivalent to those of diffraction and interference associated with the use of extended sources. The relative importance of these effects may then be estimated using existing literature on diffraction corrections in radiometry. Estimates of the importance of coherence may be made from comparison of coherence dimensions with aperture sizes; where small apertures are used, coherence theory may be required to superimpose correlated fields.