  The Cherenkov Telescope Array (CTA) is the next generation of ground-based
very high energy gamma-ray instruments; the facility will be organized in two
arrays, one for each hemisphere. The atmospheric calibration of the CTA
telescopes is a critical task. The atmosphere affects the measured Cherenkov
yield in several ways: the air-shower development itself, the variation of the
Cherenkov angle with altitude, the loss of photons due to scattering and
absorption of Cherenkov light out of the camera field-of-view and the
scattering of photons into the camera. In this scenario, aerosols are the most
variable atmospheric component in time and space and therefore need a
continuous monitoring. Lidars are among the most used instruments in
atmospheric physics to measure the aerosol attenuation profiles of light. The
ARCADE Lidar system is a very compact and portable Raman Lidar system that has
been built within the FIRB 2010 grant and is currently taking data in Lamar,
Colorado. The ARCADE Lidar is proposed to operate at the CTA sites with the
goal of making a first survey of the aerosol conditions of the selected site
and to use it as a calibrated benchmark for the other Lidars that will be
installed on site. It is proposed for CTA that the ARCADE Lidar will be first
upgraded in Italy and then tested in parallel to a Lidar of the EARLINET
network in L'Aquila. Upgrades include the addition of the water vapour Raman
channel to the receiver and the use of new and better performing electronics.
It is proposed that the upgraded system will travel to and characterize both
CTA sites, starting from the first selected site in 2016.
