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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/acp-2020-294
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-294
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  06 May 2020

06 May 2020

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This preprint is currently under review for the journal ACP.

Validation of aerosol backscatter profiles from Raman lidar and ceilometer using balloon-borne measurements

Simone Brunamonti1, Giovanni Martucci1, Gonzague Romanens1, Yann Poltera2, Frank G. Wienhold2, Alexander Haefele1, and Francisco Navas-Guzmán1 Simone Brunamonti et al.
  • 1Federal Office of Meteorology and Climatology (MeteoSwiss), Payerne, Switzerland
  • 2Swiss Federal Institute of Technology (ETH), Zürich, Switzerland

Abstract. Remote sensing measurements by light detection and ranging (lidar) instruments are fundamental for the monitoring of altitude-resolved aerosol optical properties. Here, we validate vertical profiles of aerosol backscatter coefficient (βaer) measured by two independent lidar systems using co-located balloon-borne measurements performed by Compact Optical Backscatter Aerosol Detector (COBALD) sondes. COBALD provides high-precision in-situ measurements of βaer at two wavelengths (455 and 940 nm). The two analyzed lidar systems are the research Raman Lidar for Meteorological Observations (RALMO) and the commercial CHM15K ceilometer (Lufft, Germany). We consider in total 17 RALMO and 31 CHM15K profiles, co-located with simultaneous COBALD soundings performed throughout the years 2014–2019 at the MeteoSwiss observatory of Payerne (Switzerland). The RALMO (355 nm) and CHM15K (1064 nm) measurements are converted to respectively 455 nm and 940 nm using the Angstrom exponent profiles retrieved from COBALD data. To account for the different receiver field of view (FOV) angles between the two lidars (0.01–0.02°) and COBALD (6°), we derive a custom-made correction using Mie-theory scattering simulations. Our analysis shows that both RALMO and CHM15K achieve a good agreement with COBALD measurements in the boundary layer and free troposphere, up to 6 km altitude, and including fine structures in the aerosol’s vertical distribution. For altitudes below 2 km, the mean ± standard deviation difference in βaer is + 6 % ± 40 % (+ 0.005 ± 0.319 Mm−1 sr−1) for RALMO – COBALD at 455 nm, and + 13 % ± 51 % (+ 0.038 ± 0.207 Mm−1 sr−1) for CHM15K – COBALD at 940 nm. The large standard deviations can be at least partly attributed to atmospheric variability effects, associated with the balloon’s horizontal drift with altitude (away from the lidar beam) and the different integration times of the two techniques. Combined with the high spatial and temporal variability of atmospheric aerosols, these effects often lead to a slight altitude displacement between aerosol backscatter features that are seen by both techniques. For altitudes between 2–6 km, the absolute standard deviations of both RALMO and CHM15K decrease (below 0.13 and 0.16 Mm−1sr−1, respectively), while their corresponding relative deviations increase (often exceeding 100 % COBALD of the signal). This is due to the low aerosol content (i.e. low absolute backscattered signal) in the free troposphere, and the vertically decreasing signal-to-noise ratio of the lidar measurements (especially CHM15K). Overall, we conclude that the βaer profiles measured by the RALMO and CHM15K lidar systems are in good agreement with in-situ measurements by COBALD sondes up to 6 km altitude.

Simone Brunamonti et al.

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Simone Brunamonti et al.

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Latest update: 07 Aug 2020
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Short summary
Lidar (light detection and ranging) is a class of remote sensing instruments that are widely used for the monitoring of aerosol properties in the lower levels of the atmosphere, yet their measurements are affected by several sources of uncertainty. Here we present the first comparison of two lidar systems against a fully independent instrument carried by meteorological balloons. We show that both lidars achieve a good agreement with the high precision balloon measurements up to 6 km altitude.
Lidar (light detection and ranging) is a class of remote sensing instruments that are widely...
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