04 Dec 2020

04 Dec 2020

Review status: a revised version of this preprint is currently under review for the journal AMT.

Quality assessment of Dobson spectrophotometers for ozone column measurements before and after automation at Arosa and Davos

René Stübi1, Herbert Schill2, Eliane Maillard Barras1, Jörg Klausen1, and Alexander Haefele1 René Stübi et al.
  • 1Federal Office of Meteorology and Climatology, MeteoSwiss, 1530 Payerne, Switzerland
  • 2Physikalisch-Meteorologisches Observatorium / World Radiation Center, 7260 Davos Dorf, Switzerland

Abstract. The longest ozone column measurements series are based on the Dobson sun spectrophotometers developed in the 1920s by Prof. G. B. W. Dobson. These instruments still constitute an important part of the World Meteorological Organization's global network due to their optical qualities and ruggedness. The primary drawback of this instrument is the effort needed for its manual operation. In industrialized and some lesser developed countries, most stations have made the choice to replace the Dobson by the automated Brewer sun spectrophotometers but some are still relying on the Dobson instrument. One of them is the Arosa station where both instrument types are run in parallel. Here, an automated version of the Dobson instrument was developed and implemented recently. In the present paper, the results of the analysis of simultaneous measurements from pairs of Dobson instruments that were either collocated at Arosa or Davos, or operated one at each location, are presented for four distinct time periods:

– 1992–2012 : Manual vs. Manual operation of Collocated Dobson instruments (MMC)

– 2012–2013 : Manual vs. Automated operation of Collocated Dobson instruments (MAC)

– 2012–2019 : Automated vs. Automated operation of Collocated Dobson instruments (AAC) and

– 2016–2019 : Automated vs. Automated operation of Distant Dobson instruments (AAD)

The direct comparison of two instruments using the standard operation procedure during the MMC period gives a metric necessary to validate the automated version of Dobson instruments. The direct comparison of two collocated instruments using the standard manual operation procedure reveals random differences of coincident observations with a standard deviation of ∼0.45 % and monthly mean differences between −1.0 and +0.8 %. In most cases the observed biases are not statistically significant. The same analysis of two automated Dobson instruments yields significantly smaller standard deviation of ∼0.25 % and biases of between −0.7 % and 0.8 %. This demonstrates that the repeatability has improved with the automation while the systematic differences are only marginally smaller.

The description of the automated data acquisition and control of the Dobson instrument is presented in a separate paper (Stübi et al. , 2020).

René Stübi et al.

Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

René Stübi et al.

René Stübi et al.


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Short summary
Dobson sun spectrometer instruments are used in many stations around the world to measure the ozone column. Developed in the first half of the 20s century, these instruments are manually operated which is nowadays difficult to justify in terms of ressources. To secure the well known Arosa ozone column series in the long term, a fully automated version of the Dobson instrument has been developed at MeteoSwiss. A description of this new data acquisition system is presented here.