RADIOMETRIC CALIBRATION OF SOLAR SPACE TELESCOPES - THE DEVELOPMENT OF A VACUUM-ULTRAVIOLET TRANSFER SOURCE STANDARD

The development of a source standard for the vacuum-ultraviolet spectr al region will facilitate the laboratory calibration and radiometric i ntercomparison of the coronal telescopes to be flown on ESA's Solar an d Heliospheric Observatory (Soho) spacecraft. Perhaps surprisingly, th e Sun's output in this spectral region is not well known, because vari ations in the output itself, and those due to the instrument-sensitivi ty and radiometric-calibration uncertainties of earlier space telescop es, could not be satisfactorily resolved. Radiometric intercomparison of Soho's instruments on the ground, strict attention to cleanliness, and in-orbit inter-comparisons are providing the means for vastly impr oved solar radiometry, which is of interest not only to astrophysicist s but also to aeronomists.