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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 10, 4253-4277, 2017
https://doi.org/10.5194/amt-10-4253-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
10 Nov 2017
Depolarization calibration and measurements using the CANDAC Rayleigh–Mie–Raman lidar at Eureka, Canada
Emily M. McCullough1,2, Robert J. Sica1, James R. Drummond2, Graeme Nott2,a, Christopher Perro2, Colin P. Thackray2, Jason Hopper2, Jonathan Doyle2, Thomas J. Duck2, and Kaley A. Walker3 1Department of Physics and Astronomy, The University of Western Ontario, 1151 Richmond St., London, ON, N6A 3K7, Canada
2Department of Physics and Atmospheric Science, Dalhousie University, 6310 Coburg Rd., P.O. Box 15000, Halifax, NS, B3H 4R2, Canada
3Department of Physics, University of Toronto, 60 St. George St., Toronto, Ontario, M5S 1A7, Canada
apresent address: Facility for Airborne Atmospheric Measurements, Building 146, Cranfield University, Cranfield, MK43 0AL, UK
Abstract. The Canadian Network for the Detection of Atmospheric Change (CANDAC) Rayleigh–Mie–Raman lidar (CRL) at Eureka, Nunavut, has measured tropospheric clouds, aerosols, and water vapour since 2007. In remote and meteorologically significant locations, such as the Canadian High Arctic, the ability to add new measurement capability to an existing well-tested facility is extremely valuable. In 2010, linear depolarization 532 nm measurement hardware was installed in the lidar's receiver. To minimize disruption in the existing lidar channels and to preserve their existing characterization so far as is possible, the depolarization hardware was placed near the end of the receiver cascade. The upstream optics already in place were not optimized for preserving the polarization of received light. Calibrations and Mueller matrix calculations are used to determine and mitigate the contribution of these upstream optics on the depolarization measurements. The results show that with appropriate calibration, indications of cloud particle phase (ice vs. water) through the use of the depolarization parameter are now possible to a precision of ±0.05 absolute uncertainty ( ≤ 10 % relative uncertainty) within clouds at time and altitude resolutions of 5 min and 37.5 m respectively, with higher precision and higher resolution possible in select cases. The uncertainty is somewhat larger outside of clouds at the same altitude, typically with absolute uncertainty  ≤ 0.1. Monitoring changes in Arctic cloud composition, including particle phase, is essential for an improved understanding of the changing climate locally and globally.

Citation: McCullough, E. M., Sica, R. J., Drummond, J. R., Nott, G., Perro, C., Thackray, C. P., Hopper, J., Doyle, J., Duck, T. J., and Walker, K. A.: Depolarization calibration and measurements using the CANDAC Rayleigh–Mie–Raman lidar at Eureka, Canada, Atmos. Meas. Tech., 10, 4253-4277, https://doi.org/10.5194/amt-10-4253-2017, 2017.
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Short summary
CRL lidar in the Canadian High Arctic uses lasers and a telescope to study polar clouds, essential for understanding the changing global climate. Hardware added to CRL allows it to measure the polarization of returned laser light, indicating whether cloud particles are liquid or frozen. Calibrations show that traditional analysis methods work well, although CRL was not originally set up to make this type of measurement. CRL can now measure cloud particle phase every 5 min, every 37.5 m, 24h/day.
CRL lidar in the Canadian High Arctic uses lasers and a telescope to study polar clouds,...
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