PARTIAL COHERENCE AND PRACTICAL RADIOMETRY

A review is presented of recent claims on the effects of partial coher ence in radiometric measurements. particularly in relation to spectral irradiance intercomparisons. It is shown that for practical sources t ypically used in radiometric laboratories, effects claimed to be due t o partial coherence are equivalent to those of diffraction and interfe rence associated with the use of extended sources. The relative import ance 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 b e required to superimpose correlated fields.