The VIRGO’s primary channel’s TSI values (PMO6V-A, shifted downward by 0.3 W m⁻²) are shown in magenta. This channel’s sensitivity has decreased by more than 4000 ppm following an initial 500 ppm increase at the beginning of the mission. This degradation pattern is very similar to that of the PREMOS, although the VIRGO’s degradation occurred over a much longer time range. (The blue line shows the VIRGO’s DIARAD-R channel’s irradiance measurements shifted downward by 4.5 W m⁻², the blue diamonds indicate the lesser-used DIARAD-L, and the red asterisks the lesser-used PMO6V-B shifted downward by 1.7 W m⁻².) (plot courtesy of VIRGO team)