Observation of total solar irradiance

Since 1978, 7 independent experiments (Nimbus-7/ERB, SMM/ACRIM I, ERBS/ERBE, UARS/ACRIM II, SOHO/VIRGO, ACRIMSAT/ACRIM III and EOS/SORCE) started in succession for long-term monitoring total solar irradiance. These experiments are described, and 3 TSI composites constructed by the datasets of these experiments are introduced. The differences of the original data, composite approach and trend of the 3 TSI composites are shown. The argument of the different trends of the 3 TSI composites is discussed, and a conclusion is gotten that low accuracy, low quality and the relative shortage of the early TSI measurement data are the substantial reasons of the differences among the 3 TSI composites.