Astrophysics (Index)About

red noise

(Brown noise, Brownian noise)
(noise tending toward lower frequencies)

Red noise is a term for randomness in signals that is not totally uncorrelated (e.g., white noise) but has a particular frequency distribution with more of the lower frequencies (so-named because the color red comprises the lower frequencies of visible light). The term is often used specifically for the case where the power at a particular frequency is related to the reciprocal of the square of the frequency (1/f²). It is also called Brown noise or Brownian noise because Brownian motion matches it.

The term is used in discussion of signal detection. One example is the detection of extra-solar planets through astrometry, for which measurement noise is due to equipment and atmospheric anomalies.

For random noise with some other frequency distributions, the analogous terms: pink noise, blue noise, and violet noise are used:

term tendency relation to frequency
white noise same regardless of frequency constant
pink noise falls with frequency ~1/f
red noise more pronounced fall ~1/f²
blue noise rises with frequency ~f
violet noise more pronounced rise ~f²

Further reading: