(1) Random electrical signals, generated by circuit components or by natural disturbances, that make transmitted Data inaccurate by introducing errors. (2) Any unwanted disturbance affecting a measurement (as of a Frequency band), especially that which degrades the information-bearing quality of the data of interest. Noise determines the precision with which a radiometric measurement can be made. The standard deviation of a measurement is a common method for defining noise. Noise includes systematic or random sources. Systematic noise is constant or modelable with time and includes coherent noise, scan-correlated-shift, Banding and striping and others, which reduce the ability to extract information from images. Systematic noise is potentially reducible with Ground processing. Random noise, or white noise, is not correctable, but the uncertainty of estimates of the mean value can be reduced by multiple measurements, which are subject only to random noise. The potential Degradation of signal from variations in the analog reference signal from space are reduced by using analog-to-digital converters and then adding Error Correction code to the Digital signal to allow the exact original digital number to be recovered in ground processing even IF it was degraded in transit. Also see banding, coherent noise, background noise, scan-correlated-shift and signal-to-noise ratio. (Source: Dr. John Barker)