The Nimbus 7 solar total irradiance - A new algorithm for its derivation

A new analysis is presented of the Nimbus-7 cavity radiometer measurements of the solar total irradiance from November 1978 to July 1991. Several problems concerning Nimbus 7 measurements are identified, and a new algorithm is developed for deriving the solar irradiance from Nimbus-7 raw data, which removes more of the instrumental and geometrical influences on the measurements than did previous algorithms. Compared to previous analyses of Nimbus-7 radiometer, the new values are higher and somewhat less variable than the older values. Compared to SMM measurements, the new values agree with SMM data quite well as long as any solar activity is present, but when the sun is quiet and its irradiance variability is less than the Nimbus radiometer resolution, the comparison breaks down.