The ratio of the level of the information-bearing signal power to the level of the noise power. SNR determines the precision of a radiometric measurement. The signal-to-noise ratio (SNR) is defined as the value of a measurement over the standard deviation of the measurement and is therefore a unitless variable. Typically, sets of visible reflective bands or sets of emissive bands on a scanner are designed to have approximately equal SNRs, with exceptions being made for poorer SNR in a panchromatic sharpening band as a cost of the higher spatial resolution. SNR is often taken as a time average over both random and systemic variations, however it can be a measure of either total or random noise only. SNR usually increases with increasing signal. Also see noise.