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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 4
Atmos. Meas. Tech., 11, 1989-1999, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue: Quadrennial Ozone Symposium 2016 – Status and trends...

Atmos. Meas. Tech., 11, 1989-1999, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 Apr 2018

Research article | 09 Apr 2018

Optical characterisation of three reference Dobsons in the ATMOZ Project – verification of G. M. B. Dobson's original specifications

Ulf Köhler1, Saulius Nevas2, Glen McConville3, Robert Evans3, Marek Smid4, Martin Stanek5, Alberto Redondas6, and Fritz Schönenborn1 Ulf Köhler et al.
  • 1Met. Obs. Hohenpeissenberg, Deutscher Wetterdienst, Albin-Schwaiger-Weg 10, 82383 Hohenpeissenberg, Germany
  • 2Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany
  • 3ESRL, R/GMD1, NOAA, 325 Broadway, Boulder, CO 80305, USA
  • 4Czech Metrology Institute, Okruzni 31, 638 00 Brno, (Dept. of Optics, Prague), Czech Republic
  • 5Solar and Ozone Observatory, Czech Hydrometeorological Institute, Zamecek 456, 500 08 Hradec Kralove 8, Czech Republic
  • 6Izaña Atmospheric Research Centre, AEMET- Meteorological State Agency, C/La Marina 20, 6 Planta, 38071 Santa Cruz de Tenerife, Spain

Abstract. Three reference Dobsons (regional standard Dobsons No. 064, Germany and No. 074, Czech Republic as well as the world standard No. 083, USA) were optically characterized at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig in 2015 and at the Czech Metrology Institute (CMI) in Prague in 2016 within the EMRP ENV 059 project Traceability for atmospheric total column ozone. Slit functions and the related parameters of the instruments were measured and compared with G. M. B. Dobson's specifications in his handbook. All Dobsons show a predominantly good match of the slit functions and the peak (centroid) wavelengths with deviations between −0.11 and +0.12nm and differences of the full width half maximum (FWHM) between 0.13 and 0.37nm compared to the nominal values at the shorter wavelengths. Slightly larger deviations of the FWHMs from the nominal Dobson data, up to 1.22nm, can be seen at the longer wavelengths, especially for the slit function of the long D-wavelength. However, differences between the effective absorption coefficients (EACs) for ozone derived using Dobson's nominal values of the optical parameters on one hand and these measured values on the other hand are not too large in the case of both old Bass–Paur (BP) and new IUP-ozone (Institut für Umweltphysik, University of Bremen) absorption cross sections. Their inclusion in the calculation of the total ozone column (TOC) leads to improvements of significantly less than ±1% at the AD-wavelengths between −1 and −2% at the CD-wavelengths pairs in the BP-scale. The effect on the TOC in the IUP-scale is somewhat larger at the AD-wavelengths, up to +1% (D074), and smaller at the CD-wavelengths pair, from −0.44 to −1.5%. Beside this positive effect gained from the data with higher metrological quality that is needed for trend analyses and satellite validation, it will be also possible to explain uncommon behaviours of field Dobsons during calibration services, especially when a newly developed transportable device TuPS (tuneable portable radiation source) from CMI proves its capability to provide similar results as the stationary setups in the laboratories of National Metrology Institutes. Then, the field Dobsons can be optically characterized as well during regular calibration campaigns. A corresponding publication will be prepared using the results of TuPS-based measurements of more than 10 Dobsons in field campaigns in 2017.

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Short summary
Laboratory investigations of optical characteristics of three standard Dobsons provide real wavelength settings and slit functions. These parameters were compared with the original values given in the manuals. The differences between real and nominal values are not too large, but their application will in any case improve the quality of the total ozone column measurements in the global network. This improvement was the main objective of the ATMOZ project funding these activities.
Laboratory investigations of optical characteristics of three standard Dobsons provide real...