Installation and calibration of the depolarization channel of the CANDAC Rayleigh-Mie-Raman Lidar in the Canadian High Arctic

The Canadian Network for the Detection of Atmospheric Change (CANDAC) Rayleigh-Mie-Raman Lidar (CRL) was installed in the Canadian High Arctic at Eureka, Nunavut (80°N, 86°W) in 2008-2009. The remotely-operated system began with measurement capabilities for multi-wavelength aerosol extinction, water vapour mixing ratio, and tropospheric temperature profiles, as well as particulate density and colour ratio. In 2010, a new depolarisation channel was added, which provides measurements used to discern between ice crystal, liquid water, and aerosol returns. This is an important measurement capacity during the Arctic winter particularly due to the occurrence of tropospheric mixed-phase clouds. These clouds have significantly different radiative properties compared to the more usual ice clouds. Many depolarization-capable lidar systems use two separate detector channels: one for the component of the backscattered lidar return which is parallel to the transmitted laser light, and one for the component which is perpendicular. The CRL, instead, uses a rotating Glan-Thompson prism to allow perpendicular and parallel light through to a single PMT on alternate laser shots. This approach simplifies the calibration of the depolarization measurements because no corrections are needed to account for differences in sensitivity of two physically separate measurement channels. Details of the depolarization channel installation, calibration and some first results will be discussed.