1064 nm rotational Raman polarization lidar for profiling aerosol and cloud characteristics.

The vertical profiles of aerosol or mixed-phase cloud optical properties (e.g. extinction coefficient) at 1064 nm are difficult to obtain from lidar observations. Based on the techniques of rotational Raman signal at 1058 nm described by Haarig et al. [Atmos. Meas. Tech.9, 4269 (2016)10.5194/amt-9-4269-2016], we have developed a novel rotational Raman polarization lidar at 1064 nm at Wuhan University. In this design, we optimized the central wavelength of the rotational Raman channel to 1056 nm with a bandwidth of 6 nm to increase the signal-to-noise ratio and minimize the temperature dependence of the extracted rotational Raman spectrum. And then separated elastic polarization channels (1064 nm Parallel, P and 1064 nm Cross, S) into near range (low 1064 nm P and 1064 nm S) and far range detection channels (high 1064 nm P and 1064 nm S) to extend the dynamic range of lidar observation. Silicon single photon avalanche diodes (SPAD) working at photon counting mode were applied to improve the quantum efficiency and reduce the electronic noise, which resulted in quantum efficiency of 2.5%. With a power of 3 W diode pumped pulsed Nd:YAG laser and aperture of 250 mm Cassegrain telescope, the detectable range can cover the atmosphere from 0.3 km to the top troposphere (about 12-15 km). To the best of our knowledge, the design of this novel lidar system is described and the mixed-phase cloud and aerosol optical properties observations of backscatter coefficients, extinction coefficients, lidar ratio and depolarization ratio at 1064 nm were performed as demonstrations of the system capabilities.