10 Oct 2022
10 Oct 2022
Status: this preprint is currently under review for the journal AMT.

Spectrometric fluorescence and Raman lidar: Absolute calibration of aerosol fluorescence spectra and fluorescence correction of humidity measurements

Jens Reichardt, Oliver Behrendt, and Felix Lauermann Jens Reichardt et al.
  • Richard-Aßmann-Observatorium, Deutscher Wetterdienst, Lindenberg, Germany

Abstract. RAMSES is the operational spectrometric fluorescence and Raman lidar at the Lindenberg Meteorological Observatory. It employs three spectrometers, with the UVA spectrometer (378–458 nm spectral range) being the latest to be implemented in 2018. The UVA spectrometer extends the fluorescence measurement range to shorter wavelengths than previously accessible, and its water vapor measurements can be corrected for fluorescence effects. First the new experimental setup of the RAMSES near-range receiver, which integrates the UVA spectrometer, is described. Then it is detailed how the fluorescence measurement with the UVA spectrometer is absolutely calibrated and how the fluorescence spectra are merged with those obtained with the second fluorescence spectrometer (440–750 nm spectral range). The second part of this study is dedicated to the effect of aerosol fluorescence on water vapor measurements with Raman lidars. When aerosols are present, a fluorescence-induced error always arises and therefore requires thorough analysis, even though it is particularly significant (in relative terms) only when the atmosphere is dry, the fluorescence signal strong, or the bandwidth of the Raman detection channels wide. For moisture measurements with the UVA spectrometer, a method is introduced that effectively eliminates the systematic fluorescence error. However, the increase in trueness comes at the expense of precision. The investigations further show that an accurate correction for fluorescence is impossible when the Raman lidar is not equipped with a spectrometer but with a single fluorescence receiver channel only, at least for biomass burning aerosol, because for a given fluorescence backscatter coefficient at the wavelength of the auxiliary detection channel the induced error in humidity can vary widely due to the changing shape of the fluorescence spectrum, which depends on aerosol type and atmospheric state and possibly also on other factors.

Jens Reichardt et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-276', Anonymous Referee #1, 22 Oct 2022
    • AC1: 'Reply on RC1', Jens Reichardt, 30 Nov 2022
  • RC2: 'Comment on amt-2022-276', Anonymous Referee #2, 05 Nov 2022
    • AC2: 'Reply on RC2', Jens Reichardt, 30 Nov 2022
  • RC3: 'Comment on amt-2022-276', Anonymous Referee #3, 17 Nov 2022
    • AC3: 'Reply on RC3', Jens Reichardt, 30 Nov 2022

Jens Reichardt et al.

Jens Reichardt et al.


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Short summary
The UVA spectrometer is the latest instrumental addition to the spectrometric fluorescence and Raman lidar RAMSES. The redesigned receiver and the data analysis of the fluorescence measurement are described. Furthermore, the effect of aerosol fluorescence on humidity measurements is studied. It turns out that Raman lidars equipped with a spectrometer show superior performance over those with one discrete fluorescence detection channel only. The cause is variability in the fluorescence spectrum.