— 16 — White Light Inter-calibrations of UVCS, LASCO-C2 and Spartan 201/WLC RICHARD A. FRAZIN Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA MARCO ROMOLI Dip. di Astronomia e Scienza dello Spazio Universit` a di Firenze, Firenze, Italy J OHN L. KOHL,LARRY D. GARDNER Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA DENNIS WANG,RUSSELL A. HOWARD E.O. Hulburt Center for Space Research Naval Research Laboratory, Washington, DC, USA THERESE A. KUCERA NASA Goddard Space Flight Center, Greenbelt, MD, USA This paper describes comparisons among white light polarized radiances (pB) as mea- sured by the Ultraviolet Coronagraph Spectrometer White Light Channel (UVCS/WLC), the Large Angle and Spectrometric Coronagraph Experiment C2 instrument (LASCO- C2) and the Spartan 201 White Light Coronagraph (Spartan 201/WLC). UVCS/WLC and LASCO-C2 are generally in agreement, although there are some systematic trends and discrepancies that still require explanation. UVCS/WLC and Spartan 201/WLC agree to within the measurement uncertainties. Spartan 201/WLC and LASCO-C2 are not directly compared to each other in this paper. 16.1 Introduction The UVCS White Light Channel (UVCS/WLC; Kohl et al. [1995]), the Large Angle and Spectrometric Coronagraph Experiment C2 instrument (LASCO-C2; Brueckner et al. [1995]), and the Spartan 201 White Light Coronagraph (Spartan 201/WLC; Fisher and Guhathakurta [1994]) all measure the polarized radiance (pB) of the solar corona. In this paper we present a systematic comparison of their pB measurements. A paper that describes the calibration of Spartan 201/WLC and a direct inter-comparison of LASCO- C2 and the Spartan 201/WLC is in preparation [Kucera, 2002]. Although the UVCS/WLC calibration is still in progress, for the purposes of this paper we adopt the in-flight calibration that is described in Romoli et al. [2002], which also gives 1