Determining atmospheric aerosol content with an infra-red radiometer

Abstract

The attenuation of atmospheric Cherenkov photons is dominated by two processes: Rayleigh scattering from the molecular component and Mie scattering from the aerosol component. Aerosols are expected to contribute up to 30 Wm${}^{-2}$ to the emission profile of the atmosphere, equivalent to a difference of $\sim 20^{\circ }$C to the clear sky brightness temperature under normal conditions. Here we investigate the aerosol contribution of the measured sky brightness temperature at the H.E.S.S. site; compare it to effective changes in the telescope trigger rates; and discuss how it can be used to provide an assessment of sky clarity that is unambiguously free of telescope systematics.

4 pages. To be published in High Energy Gamma-Ray Astronomy (eds. F. Aharonian, W. Hofmann, F. Rieger) the proceedings of the 5th Heidelberg international symposium on high energy gamma-ray astronomy