Engineering of a water-vapour, Raman, elastic-backscatter Lidar at the Technical University of Catalonia (Spain)

摘要

Implementation of the pure-vibrational Raman spectra lidar method for simultaneous measurements of atmospheric water-vapour, aerosol extinction and backscatter coefficients is reported. A Q-switched Nd:YAG laser provides the three elastic wavelengths of 1064, 532 and 355 nm while the return signal is collected by a 40-cm aperture telescope. A spot-to-spot fiber bundle conveys the light from the telescope focal plane to a specific polychromator especially simulated and designed with care on minimizing optical losses and physical dimensions. The reception field of view, which is limited by the fiber bundle characteristics, is the same for all wavelengths. By means of four customised dichroic filters and beam splitters, light is separated into the three elastic wavelengths (355, 532, 1064 nm) as well as the 386.7- and 607.4-nm N_2-Raman-shifted wavelengths, and the 407.5-nm H_2O-Raman-shifted wavelength. Signal detection is achieved by using avalanche photodiodes at 1064 and 532 nm and analog acquisition while photomultiplier tubes and fast photon counting acquisition at the rest of the wavelengths. A specific design of the optoelectronics of the receiving channels is controlled by a distributed CPU thanks to a user-friendly LabViewTM interface. User-configurable scanning tools are built-in, but can also be customized. In this work an overview of the system though particularly geared to the polychromator unit is presented as well as a power link-budget assessment, which is to include simulation of end-to-end transmissivities, will be discussed for the main channels involved. The first measurements have already been made at 1064, 532, and 607.4 nm.