Title: Raman LIDARs and atmospheric calibration for the Cherenkov Telescope Array,
Abstract: The Cherenkov Telescope Array (CTA) is the next generation of Imaging
Atmospheric Cherenkov Telescopes. It will reach a sensitivity and energy
resolution never obtained until now by any other high energy gamma-ray
experiment. Understanding the systematic uncertainties in general will be a
crucial issue for the performance of CTA. It is well known that atmospheric
conditions contribute particularly in this aspect.Within the CTA consortium
several groups are currently building Raman LIDARs to be installed on the two
sites. Raman LIDARs are devices composed of a powerful laser that shoots into
the atmosphere, a collector that gathers the backscattered light from molecules
and aerosols, a photo-sensor, an optical module that spectrally selects
wavelengths of interest, and a read--out system.Unlike currently used elastic
LIDARs, they can help reduce the systematic uncertainties of the molecular and
aerosol components of the atmosphere to <5% so that CTA can achieve its energy
resolution requirements of<10% uncertainty at 1 TeV.All the Raman LIDARs in
this work have design features that make them different than typical Raman
LIDARs used in atmospheric science and are characterized by large collecting
mirrors (2.5m2) and reduced acquisition time.They provide both multiple elastic
and Raman read-out channels and custom made optics design.In this paper, the
motivation for Raman LIDARs, the design and the status of advance of these
technologies are described.