### signal-to-noise ratio

**(SNR, S/N)**
(ratio of the power of a signal to the power of the background noise)

**Signal-to-noise ratio** (**SNR**) is a measure of a receiver's
intended signal as opposed to background noise,
expressed as a ratio of the average power of each
(**signal-to-noise**, **SN**).
The power (of each) is directly related to the
square of its root-mean-square amplitude
i.e., the mean of the amplitude squared.
*Signal-to-noise ratio* is also expressed in decibels,
as 10 times the log 10 of the power ratio above.
As the log of a ratio, zero means "signal equals noise",
and greater than zero means the signal is stronger than
the noise.

In astrophysics, the signal-to-noise ratio may be
used to characterize the possibility of sensing
the output of an astrophysical phenomenon above the
background signal and distortion. It is generally
applicable but is key in all electronic sensors
such as CCDs, and radio telescope
antennas and receivers.
Such SNR is sometimes expressed as parts per million (PPM) of
the "normal" signal, and the variation of interest in the signal
is also so-expressed. (I assume such a quoted PPM indicates SNR
divided by a million, but I also wonder whether sometimes a quoted PPM
is for "signal divided by the sum of signal and noise").

(*engineering,measure,ratio*)
**Further reading:**

http://en.wikipedia.org/wiki/Signal-to-noise_ratio

**Referenced by pages:**

combined differential photometric precision (CDPP)

detective quantum efficiency (DQE)

GW170817

HCI

noise-equivalent power (NEP)

NuSTAR

photodiode

point source sensitivity

radiometer equation

speckle suppression

stacking

Index