  The CTA is the next generation of ground based very high energy gamma ray
Imaging Atmospheric Cherenkov Telescopes. Since observations with this
technique are affected by atmospheric conditions, an accurate knowledge of the
atmospheric properties is fundamental to improve the precision and duty cycle
of the CTA. Measurements of absorption and scattering properties of the
atmosphere due to aerosols and molecules can be used in the event
reconstruction or in MODTRAN, an analytical code designed to model the
propagation of electromagnetic radiation. MODTRAN output is used as an input
for the air shower simulation and Cherenkov light production, giving the
optical depth profiles that together with the refractive index allow the proper
simulation of the gamma ray induced signals and a correct measurement of the
primary energy from the detected signals. The ARCADE Raman Lidar will be used
for the on site characterization of the aerosol attenuation profiles of the UV
light. The collected data will be used in preparation for the full operation of
the array, providing nightly information about the aerosol properties such as
the vertical aerosol optical depth and the water vapour mixing ratio with an
altitude resolution better than 100 m from about 400 m to 10 km above ground
level. These measurements will help to define the needs for Monte Carlo
simulations of the shower development and of the detector response. This
instrument will also be used for the intercalibration of the future Raman
Lidars that are expected to operate at the CTA sites. This contribution
includes a description of the ARCADE Lidar and the characterization of the
performance of the system. The system is expected to be shipped to the northern
site of the CTA (La Palma) before the end of 2017, to acquire data locally for
1 year before being moved to the southern site (Chile).
