  The H.E.S.S. experiment in Namibia is a high-energy gamma-ray telescope
sensitive in the energy range from 30 GeV to a several tens of TeV, that uses
the atmospheric Cherenkov technique to detect showers developed within the
atmosphere. The elastic lidar, installed on the H.E.S.S. site, allows to reduce
the systematic errors related to the atmospheric composition uncertainties
thanks to the estimation of the extinction profile for the Cherenkov light
(300-650 nm). The latter has a direct impact on the reconstructed parameters,
such as the photon energy and the source flux. In this paper we report on
physics results obtained on the Crab Nebula spectrum using the lidar profiles
obtained at the H.E.S.S. site.
