Ground-based Ring-effect measurements with the OSIRIS development model

The Ring effect is measured using the UV–visible spectrometer (~1 nm spectral resolution) of OSIRIS, the optical spectrograph and infrared imaging system. The observed filling in of Ca(II) H and K (~395 nm), the two largest Fraunhofer lines in the solar spectrum, are compared with the filling in simulated with a new model that includes rotational Raman scattering (RRS) by N2 and O2. The filling in is (1.06 ± 0.60)% at Ca(II) K and (1.40 ± 0.50)% at Ca(II) H for blue-sky observations at a solar zenith angle of 37°. The measured filling in agrees with the modelled filling in within the uncertainties. PACS Nos.: 07.60Rd, 33.20Fb, 42.68Ay, 42.68Ca, 42.68Ge, 42.68Mj