MUSA (Multiwavelength System for Aerosol) is a mobile multi-wavelength lidar system based on a Nd:YAG laser equipped with second and third harmonic generators and on a Cassegrain telescope with a primary mirror of 300mm diameter.

The three laser beams at 1064, 532 and 355nm are simultaneously and coaxially transmitted into the atmosphere in biaxial configuration. The receiving system has 3 channels for the detection of the radiation elastically backscattered from the atmosphere and 2 channels for the detection of the Raman radiation backscattered by the atmospheric N2 molecules at 607 and 387 nm. The elastic channel at 532 nm is split into parallel and perpendicular polarization components by means of a polarizer beamsplitter cube. The backscattered radiation at all the wavelengths is acquired both in analog and photon counting mode. The calibration of depolarization channels is made automatically using the ±45 method. The typical vertical resolution of the raw profiles is 3.75m with a temporal resolution of 1 min.

The system is compact and transportable. It was developed in 2009 in cooperation with the Meteorological Institute of the Ludwig-Maximilians-Universität of Munich and it is one of the reference systems used in the frame of the EARLINET Quality Assurance programme.

The system was involved in two intercomparison measurement campaigns within the FP6 project EARLINET-ASOS: EARLI09 (EARLINET Lidar Intercomparison, held il Leipzig-Germany in May 2009, involving 11 lidar systems) and SPALI10 (SPAin Lidar Intercomparison, held in Madrid-Spain in 2010).