INSTRUMENTS ,

Since the early 1990s, the Earth and Atmosphere Observation Group (GOTA) of the University of La Laguna (ULL) has performed its scientific task in the area of Atmospheric Physics. Among its lines of research, it has paid special attention to atmospheric aerosols and the role they play in the climatic field. In this respect, the national R&D projects CLI1997-453, CLI2000-0903-C08, REN2001-0659-C03-02/CLI, CGL2004-05984-C07-05/CLI and more recently CGL2005-03428-C04-02/CLI, along with the European project CLIMAAT, MAC/2.3/A3 (Interreg IIIB), have been addressed to the physical and chemical study of these atmospheric particles. It must be taken into account that the Canary Islands are subjected to substantial invasions of dust from Africa (Sahara, Sahel) which present notably different behaviour depending on the time of year. To carry out this research, the GOTA acquired a lidar system based on a Q-switch pulsed Nd:YAG laser, fitted with a frequency doubler that enables it to emit light pulses at 1064 nm and 532 nm of some 10 ns of duration and around 100 mJ at 1064 nm and 50 mJ at 532 nm. In reception it uses a telescope of 20 cm aperture and photoreceivers with PMTs. The ULL’s lidar has been in operation since its installation in March 2004, following a strict measurement protocol. This consists in taking measurements on three consecutive days, shifting the observations by one day in the following week (e.g., 1st week M-Tu-W, 2nd week Tu-W-Th, etc.). In dust invasion conditions, the measurements are taken during all the days they last, including previous and subsequent days. During this year the equipment will be modified to enable it to measure in three channels simultaneously. In this way, it will be possible to measure at will: 1064 nm and 532 nm polarised vertically and horizontally; or the 1064, 532 and 355 nm channels. To do this, the PMT of the 1064 channel will be replaced by an APD, a third PMT will be added, and a higher-powered laser will be acquired, capable of emitting in the three wavelengths mentioned. The GOTA is now waiting for the material necessary for updating the equipment to arrive: the great weight of this instrument makes it very difficult to transport.