Reference: Fröhlich, C. and Lean, J.: 1998, Total solar irradiance variations: The construction of a composite and its comparison with models, in F. L. Deubner (ed.), IAU Symposium 185: New Eyes to See Inside the Sun and Stars, Kluwer Academic Publ., Dortrecht, The Netherlands, pp. 89-102, 1998. (preprint as postscript file).

See also:
The VIRGO homepage
VIRGO Total Solar Irradiance