The IMAA Raman lidar system for water vapour measurements has been operational at CNR-IMAA since July 2002. It performs measurements simultaneously with PEARL. This system is based on a Nd:YAG laser with a repetition rate up to 100 Hz and typically operating at 50 Hz. Radiation at 355nm is transmitted into the atmosphere coaxially with respect to a F/10 Cassegrain telescope used as a receiver. The telescope is of the same type as PEARL. The backscattered radiation is selected by means of dichroic mirrors and interferential filters and then is split into three channels, corresponding to the elastic backscattered radiation at 355 nm, the N2 Raman shifted signal at 386.7nm and the water vapour Raman shifted signal at 407 nm. Interferential filter bandwidths are kept below 1.0nm and 0.3nm for nighttime and daytime operations, respectively, thus, reducing the solar background during daytime measurements and limiting the effects of both atmospheric temperature variations on the measured signals and interferences from liquid water Raman scattering . As for PEARL, the spectrally selected radiation is then split for each wavelength into two channels in order to preserve the linearity of the lidar signals over all altitude ranges. Photomultiplier tubes are used as detectors and both low and high range signals are acquired in photon counting mode. The typical vertical resolution of the raw profiles is 15m with a temporal resolution of 1 min.

 

Contact person: Aldo Amodeo