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

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Atmos. Meas. Tech., 9, 3769-3791, 2016
https://doi.org/10.5194/amt-9-3769-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
17 Aug 2016
Recommendations for processing atmospheric attenuated backscatter profiles from Vaisala CL31 ceilometers
Simone Kotthaus1, Ewan O'Connor1,2, Christoph Münkel3, Cristina Charlton-Perez4, Martial Haeffelin5, Andrew M. Gabey1, and C. Sue B. Grimmond1 1Department of Meteorology, University of Reading, Reading, RG6 6BB, UK
2Finnish Meteorological Institute, 00101 Helsinki, Finland
3Vaisala GmbH, 22607 Hamburg, Germany
4Met Office, Meteorology Building, University of Reading, Reading, RG6 6BB, UK
5Institute Pierre Simon Laplace, Centre National de la Recherche Scientifique, École Polytechnique, 91128 Palaiseau, France
Abstract. Ceilometer lidars are used for cloud base height detection, to probe aerosol layers in the atmosphere (e.g. detection of elevated layers of Saharan dust or volcanic ash), and to examine boundary layer dynamics. Sensor optics and acquisition algorithms can strongly influence the observed attenuated backscatter profiles; therefore, physical interpretation of the profiles requires careful application of corrections. This study addresses the widely deployed Vaisala CL31 ceilometer. Attenuated backscatter profiles are studied to evaluate the impact of both the hardware generation and firmware version. In response to this work and discussion within the CL31/TOPROF user community (TOPROF, European COST Action aiming to harmonise ground-based remote sensing networks across Europe), Vaisala released new firmware (versions 1.72 and 2.03) for the CL31 sensors. These firmware versions are tested against previous versions, showing that several artificial features introduced by the data processing have been removed. Hence, it is recommended to use this recent firmware for analysing attenuated backscatter profiles. To allow for consistent processing of historic data, correction procedures have been developed that account for artefacts detected in data collected with older firmware. Furthermore, a procedure is proposed to determine and account for the instrument-related background signal from electronic and optical components. This is necessary for using attenuated backscatter observations from any CL31 ceilometer. Recommendations are made for the processing of attenuated backscatter observed with Vaisala CL31 sensors, including the estimation of noise which is not provided in the standard CL31 output. After taking these aspects into account, attenuated backscatter profiles from Vaisala CL31 ceilometers are considered capable of providing valuable information for a range of applications including atmospheric boundary layer studies, detection of elevated aerosol layers, and model verification.

Citation: Kotthaus, S., O'Connor, E., Münkel, C., Charlton-Perez, C., Haeffelin, M., Gabey, A. M., and Grimmond, C. S. B.: Recommendations for processing atmospheric attenuated backscatter profiles from Vaisala CL31 ceilometers, Atmos. Meas. Tech., 9, 3769-3791, https://doi.org/10.5194/amt-9-3769-2016, 2016.
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Short summary
Ceilometers lidars are useful to study clouds, aerosol layers and atmospheric boundary layer structures. As sensor optics and acquisition algorithms can strongly influence the observations, sensor specifics need to be incorporated into the physical interpretation. Here, recommendations are made for the operation and processing of profile observations from the widely deployed Vaisala CL31 ceilometer. Proposed corrections are shown to increase data quality and even data availability at times.
Ceilometers lidars are useful to study clouds, aerosol layers and atmospheric boundary layer...
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