Articles | Volume 18, issue 5
Atmos. Chem. Phys., 18, 3185–3201, 2018
Atmos. Chem. Phys., 18, 3185–3201, 2018
Research article
 | Highlight paper
06 Mar 2018
Research article  | Highlight paper | 06 Mar 2018

Results from the Fourth WMO Filter Radiometer Comparison for aerosol optical depth measurements

Stelios Kazadzis1,11, Natalia Kouremeti1, Henri Diémoz2, Julian Gröbner1, Bruce W. Forgan3, Monica Campanelli4, Victor Estellés5, Kathleen Lantz6, Joseph Michalsky6, Thomas Carlund7, Emilio Cuevas8, Carlos Toledano9, Ralf Becker10, Stephan Nyeki1, Panagiotis G. Kosmopoulos11, Viktar Tatsiankou12, Laurent Vuilleumier13, Frederick M. Denn14, Nozomu Ohkawara15, Osamu Ijima15, Philippe Goloub16, Panagiotis I. Raptis11,1, Michael Milner3, Klaus Behrens10, Africa Barreto8,9,17, Giovanni Martucci13, Emiel Hall6, James Wendell6, Bryan E. Fabbri14, and Christoph Wehrli1 Stelios Kazadzis et al.
  • 1Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Davos, Switzerland
  • 2Aria e Atmosfera – Radiazione solare e atmosfera ARPA Valle, Saint-Christophe 11020, Italy
  • 3Standards & Metrology, Bureau of Meteorology, Docklands Vic 3008, Australia
  • 4SACI-CNR,Via Fosso del Cavaliere 100, 00133, Rome, Italy
  • 5Department of Earth Physics and Thermodynamics, Solar Radiation and Research Unit, Univ. de València, Valencia, Spain
  • 6Cooperative Institute for Research in Environmental Studies, NOAA/ESRL/GMD, Boulder, CO 80305, USA
  • 7Swedish Meteorological and Hydrological Institute, 601 76 Norrköping, Sweden
  • 8Izaña Atmospheric Research Centre, State Meteorological Agency (AEMET), Santa Cruz de Tenerife, Spain
  • 9Atmospheric Optics Group (GOA), University of Valladolid 47011, Valladolid, Spain
  • 10Deutscher Wetterdienst Meteorologisches Observatorium Lindenberg, 15848 Tauche, Germany
  • 11Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Athens, Greece
  • 12COFOVO Energy Inc., 800 King Edward Avenue, Suite 3014, Ottawa, ON, K1N 6N5, Canada
  • 13Federal Office of Meteorology and Climatology MeteoSwiss, Payerne, Switzerland
  • 14Science Systems & Applications Inc NASA Langley Science Directorate, Hampton, VA 23666, USA
  • 15Japan Meteorological Agency 1-3-4 Otemachi, Chiyoda-ku, 100-8122 Tokyo, Japan
  • 16Laboratoire d'Optique Atmosphérique, Univ. des Sciences et Technologies de Lille 159655 Villeneuve d'Ascq, France
  • 17Cimel Electronique, 75011, Paris, France

Abstract. This study presents the results of the Fourth Filter Radiometer Comparison that was held in Davos, Switzerland, between 28 September and 16 October 2015. Thirty filter radiometers and spectroradiometers from 12 countries participated including reference instruments from global aerosol networks. The absolute differences of all instruments compared to the reference have been based on the World Meteorological Organization (WMO) criterion defined as follows: 95% of the measured data has to be within 0.005 ± 0.001∕m (where m is the air mass). At least 24 out of 29 instruments achieved this goal at both 500 and 865 nm, while 12 out of 17 and 13 out of 21 achieved this at 368 and 412 nm, respectively. While searching for sources of differences among different instruments, it was found that all individual differences linked to Rayleigh, NO2, ozone, water vapor calculations and related optical depths and air mass calculations were smaller than 0.01 in aerosol optical depth (AOD) at 500 and 865 nm. Different cloud-detecting algorithms used have been compared. Ångström exponent calculations showed relatively large differences among different instruments, partly because of the high calculation uncertainty of this parameter in low AOD conditions. The overall low deviations of these AOD results and the high accuracy of reference aerosol network instruments demonstrated a promising framework to achieve homogeneity, compatibility and harmonization among the different spectral AOD networks in the near future.

Short summary
Aerosol optical depth measured from ground-based sun photometers is the most important parameter for studying the changes in the Earth's radiation balance due to aerosols. Representatives for various sun photometer types belonging to individual institutions or international aerosol networks gather every 5 years, for 3 weeks, in Davos, Switzerland, in order to compare their aeorosol optical depth retrievals. This work presents the results of the latest (fourth) filter radiometer intercomparison.
Final-revised paper