Imaging incoherent sources

Observed around a given frequency, radiation sources are said to be incoherent if their relative phases (and possibly amplitudes) vary rapidly over the duration of a measurement. This situation is frequently encountered in nature whenever independent sources are involved. In radio astronomy, this is the case with the radiation from stars and other radio sources. It is also the case in radiometry, where it is the thermal nature of the radiation that is at the root of its inconsistency.

Sonar technology distinguishes between passive and active sonars. Passive sonars listen to and process independent, uncorrelated signals. Active sonars process echoes of the transmitted signal. But these are usually decorrelated by the propagation medium.