A measure of the weakest signal discernible by a detecting system. The ratio of the amplitude of a signal above the noise level to the amplitude of the noise level itself is known as the signal-to-noise ratio. For most purposes, a minimum signal-to-noise ratio of 1 : 1 is required for the signal to be regarded as definitely detected. In the radio and infrared regions, the use of techniques such as integration, chopping, comparison with a stable laboratory source, and phase-sensitive detection can improve the basic sensitivity of the system by several orders of magnitude.
Subjects: Astronomy and Astrophysics.