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

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https://doi.org/10.5194/amt-2017-328
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
10 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).
Three-channel single-wavelength lidar depolarization calibration
Emily M. McCullough1,a, Robert J. Sica1, James R. Drummond2, Graeme Nott2,b, Christopher Perro2, and Tom J. Duck2 1Department of Physics and Astronomy, The University of Western Ontario, 1151 Richmond St., London, ON, N6A 3K7
2Department of Physics and Atmospheric Science, Dalhousie University, 6310 Coburg Rd., P.O. Box 15000, Halifax, NS, B3H 4R2
apresent address: Department of Physics and Atmospheric Science, Dalhousie University, 6310 Coburg Rd., P.O. Box 15000, Halifax, NS, B3H 4R2
bpresent address: Facility for Airborne Atmospheric Measurements, Building 146, Cranfield University, Cranfield, MK43 0AL, UK
Abstract. Linear depolarization measurement capabilities were added to the CANDAC Rayleigh-Mie-Raman lidar (CRL) at Eureka, Nunavut, in the Canadian High Arctic in 2010. This upgrade enables measurements of the phases (liquid versus ice) of cold and mixed-phase clouds throughout the year, including during polar night. Depolarization measurements were calibrated according to existing methods using parallel- and perpendicular-polarized profiles as discussed in McCullough et al. (2017). We present a new technique that uses the polarization-independent Rayleigh elastic channel in combination with one of the new polarization-dependent channels, and show that for a lidar with low signal in one of the polarization-dependent channels, this method is superior to the traditional method. The optimal procedure for CRL is to determine the depolarization parameter using the traditional method at low resolution (from parallel and perpendicular signals), and then to use this value to calibrate the high-resolution new measurements (from parallel and polarization-independent Rayleigh elastic signals). Due to its use of two high-signal-rate channels, the new method has lower statistical uncertainty, and thus gives depolarization parameter values at higher spatial-temporal resolution by up to a factor of 20 for CRL. This method is easily adaptable to other lidar systems which are considering adding depolarization capability to existing hardware.

Citation: McCullough, E. M., Sica, R. J., Drummond, J. R., Nott, G., Perro, C., and Duck, T. J.: Three-channel single-wavelength lidar depolarization calibration, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-328, in review, 2017.
Emily M. McCullough et al.
Emily M. McCullough et al.
Emily M. McCullough et al.

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Short summary
Measuring the phase (liquid/ice) of Arctic clouds is essential for understanding the changing global climate. Using a lidar, two polarized signals are usually needed. At CRL lidar, one of these signals is small, so phase measurements have low resolution. Another method can use a large unpolarized signal in place of the small polarized signal. We show how to use the original low-resolution measurement to calibrate the new high-resolution method. At CRL, this gives 20 times higher resolution.
Measuring the phase (liquid/ice) of Arctic clouds is essential for understanding the changing...
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