Argentinian multi-wavelength scanning Raman lidar to observe night sky atmospheric transmission

JUAN PALLOTTA; PABLO RISTORI; LIDIA OTERO; FERNANDO CHOUZA; DELIA RAUL; FRANCISCO GONZALEZ; ALBERTO ETCHEGOYEN; EDUARDO QUEL; CTA CONSORTIUM

Río de Janeiro

Conferencia; 33rd International Cosmic Ray Conference (ICRC2013); 2013

Centro Brasileiro de Pesquisas Físicas (CBPF)

This paper discusses the multi-wavelength scanning Raman lidar being built at Lidar Division, CEILAP (CITEDEF-CONICET) in the frame of the Argentinean Cherenkov Telescope Array (CTA) collaboration to measure the spectral characteristics of the atmospheric aerosol extinction profiles to provide better transmission calculations at the future CTA site. This lidar emits short laser pulses of 7-9 ns at 355, 532 and 1064 nm at 50 Hz with nominal energy of 125 mJ at 1064 nm. This wavelengths are also used to retrieve the atmospheric (air, aerosol and clouds) backscattered radiation in the UV, VIS and IR ranges. Raman capabilities were added in the UV and VIS wavelengths to retrieve the spectral characteristics of the aerosol extinction and the water vapor profile. Due to the expected low aerosol optical depth of the future site, the short observation period as well as the extension of the observation, an enhanced collection area is required. This system uses six 40 cm f/2.5 newtonian telescopes to avoid dealing with bigger mirror deformation, aberration issues and higher costs that imply the use of a single mirror with the same collection surface. In addition, dismounting of single mirrors for replacement or recoating will affect slightly the performance but not the operation. The additional alignment procedure has been solved by an automatic mirror alignment to follow the line of sight of the observation during the acquisition period. The system was designed to operate in hard environmental conditions, as it is completely exposed to the outside weather conditions, when its shelter is fully opened to provide 360{\deg} observations.