New Results from the GOES 13 SXI: Scattered Light and Coronal Hole Emission Measurements

On 2006 May 24 the GOES 13 satellite was launched for NOAA with the next generation Solar X-ray Imager (SXI) aboard. This instrument represents a significant step forward in performance over the previous SXI aboard GOES 12, even before that instrument suffered serious degradation. Like the previous instrument, the new instrument uses a grazing incidence optical design, but with a new detector and other improvements, it has about 10 times the sensitivity, twice the spatial resolution, and greatly reduced wide-angle scattering compared to the GOES 12 SXI. The GOES 13 SXI is now completing its 6 month checkout period and we present some observational highlights to date. Particularly, a partial eclipse of the Sun by the Moon was observed on 2006 August 24 and provided substantial diagnostic information regarding scattered light in the instrument. We quantify the instrument wide-angle scattering function and apply this function to the problem of coronal hole observations. The estimated scattering signal in coronal holes due active regions and the quiet Sun is computed and then subtracted from the observed total signal in coronal holes. The remaining signal must originate along the line of sight from the coronal hole to the instrument. For well placed coronal holes, i.e., those near disk center, there is likely no overlying emission and we estimate or place upper limits on the emission for the coronal hole itself.