process by which radiation is returned by a surface or a medium, without change in the frequency of its monochromatic components Note 1 to entry: Part of the radiation falling on a medium is reflected at the surface of the medium ("surface reflection"); another part can be scattered back from the interior of the medium ("volume reflection"). Note 2 to entry: The frequency is unchanged only if there is no Doppler effect due to the motion of the materials from which the radiation is returned. Note 3 to entry: This entry was numbered 845-04-42 in IEC 60050-845:1987.
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