Total solar irradiance absolute level from DIARAD/SOVIM on the International Space Station

Current measurements from DIARAD/VIRGO, PMO6V/VIRGO and ACRIM3 radiometers are of the same order of magnitude, but differ from TIM/SORCE by about 4.5 W m⁻². This difference is higher than the sum of the claimed individual absolute uncertainties of the instruments. In this context, the SOLAR payload on the International Space Station embarks the SOVIM package. We give the results of the differential absolute radiometer DIARAD/SOVIM and discuss its associated uncertainties. Compared to DIARAD/VIRGO, all possible efforts have been made to improve the absolute accuracy. Substantial progress has been made in the aperture area and electrical power measurements. The measured TSI value from the left channel of DIARAD/SOVIM during three days of June 2008 is 1364.50 ± 1.38 W m⁻² (Total) or ±0.49 W m⁻² (if we combine the individual contributions in quadrature). The right channel gives 1364.75 W m⁻² with the same uncertainties. These values are about 1.2 W m⁻² lower than DIARAD/VIRGO and about 4 W m⁻² higher than TIM/SORCE. The difference between the left and right channels measurements is as low as 0.25 W m⁻² which is within the improved uncertainty limits.