Total solar irradiance observations from DIARAD/VIRGO

The Differential Absolute Radiometer is making measurements of the total solar irradiance as part of the Variability of Irradiance and Gravity Oscillations experiment on the Solar and Heliospheric Observatory. We present the measurements made during its 7.8 years of operation, from 1996 until the present (2003). The aging due to UV exposure of the continuously measuring left channel is determined by comparison with the backup right channel; the loss in sensitivity of the left channel is 0.5 W/m(2) or 364 ppm over 7.8 years. A raise of the total solar irradiance from a level of 1365.5 W/m(2) at the end of the solar minimum in 1996 towards a maximum level of 1368 W/m(2) at the beginning of 2002 has been measured by DIARAD.