Early Attempts at Active Atmospheric Calibration with H.E.S.S. Phase 1
  Using data derived from the H.E.S.S. Phase 1 telescope system and a Ceilometer facility on site, a method of correcting for changing atmospheric quality based on reconstructed shower parameters is presented. The method was applied to data from the active galactic nucleus PKS 2155-304, taken during August and September 2004 when the quality of the atmosphere at the site was highly variable. Corrected and uncorrected fluxes are shown, and the method is discussed as a first step towards a more complete atmospheric calibration. 
Sam Nolan, Cameron Rulten, Gerd Puhlhofer
astro-ph.IM