  The Cherenkov Telescope Array (CTA) is the next generation of Imaging
Atmospheric Cherenkov Telescopes. It would reach unprecedented sensitivity and
energy resolution in very-high-energy gamma-ray astronomy. In order to reach
these goals, the systematic uncertainties derived from the varying atmospheric
conditions shall be reduced to the minimum. Different instruments may help to
account for these uncertainties. Several groups in the CTA consortium are
currently building Raman LIDARs to be installed at the CTA 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
photosensor, an optical module that spectrally select wavelengths of interest,
and a read-out system. Raman LIDARs can reduce the systematic uncertainties in
the reconstruction of the gamma-ray energies down to 5 % level. All Raman
LIDARs subject of this work, have design features that make them different than
typical Raman LIDARs used in atmospheric science, and are characterized by
large collecting mirrors ($\sim2~$m$^2$). They have multiple elastic and Raman
read-out channels (at least 4) 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.
