Preprints
https://doi.org/10.5194/amt-2021-385
https://doi.org/10.5194/amt-2021-385

  15 Dec 2021

15 Dec 2021

Review status: this preprint is currently under review for the journal AMT.

Traceable total ozone column retrievals from direct solar spectral irradiance measurements in the ultraviolet

Luca Egli1, Julian Gröbner1, Gregor Hülsen1, Herbert Schill1, and René Stübi2 Luca Egli et al.
  • 1Physikalisch-Meteorologisches Observatorium Davos (PMOD/WRC), 7260 Davos Dorf, Switzerland
  • 2MeteoSwiss, Payerne, Switzerland

Abstract. Total column ozone (TCO) is commonly measured by Brewer and Dobson spectroradiometers. Both types of instruments are using four wavelengths in the ultraviolet radiation range to derive TCO. For the calibration and quality assurance of the measured TCO both instrument types require periodic field comparisons with a reference instrument.

This study presents traceable TCO retrievals from direct solar spectral irradiance measurements with the portable UV reference instrument QASUME. TCO is retrieved by a spectral fitting technique derived by a minimal least square fit algorithm using spectral measurements in the wavelength range between 305 nm and 345 nm. The retrieval is based on an atmospheric model accounting for different atmospheric parameters such as effective ozone temperature, aerosol optical depth, Rayleigh scattering, SO2, ground air pressure, ozone absorption cross sections and top-of-atmosphere solar spectrum. Traceability means, that the QASUME instrument is fully characterized and calibrated in the laboratory to SI standards (International System of Units). The TCO retrieval method from this instrument is independent from any reference instrument and does not require periodic in situ field calibration.

The results show that TCO from QASUME can be retrieved with a relative standard uncertainty of less than 0.8 %, when accounting for all possible uncertainties from the measurements and the retrieval model, such as different cross sections, different reference solar spectra, uncertainties from effective ozone temperature or other atmospheric parameters. The long-term comparison of QASUME TCO with a Brewer and a Dobson in Davos, Switzerland, reveals, that all three instruments are consistent within 1 % when using the ozone absorption cross section from the University of Bremen. From the results and method presented here, other absolute SI calibrated cost effective solar spectroradiometers, such as array spectroradiometers, may be applied for traceable TCO monitoring.

Luca Egli et al.

Status: open (until 19 Jan 2022)

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  • RC1: 'Comment on amt-2021-385', Anonymous Referee #2, 12 Jan 2022 reply

Luca Egli et al.

Luca Egli et al.

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Short summary
This study presents traceable total column ozone retrievals from direct solar spectral irradiance measurements. The retrieved ozone does not require any field calibration with a reference instrument as it is required for other operational network instruments such as Brewer or Dobson. Total column ozone can be retrieved with a traceable overall uncertainty of less than 0.8 % indicating a benchmark uncertainty for total columne ozone measurements.