Articles | Volume 4, issue 8
Atmos. Meas. Tech., 4, 1689–1703, 2011
Atmos. Meas. Tech., 4, 1689–1703, 2011

Research article 31 Aug 2011

Research article | 31 Aug 2011

First national intercomparison of solar ultraviolet radiometers in Italy

H. Diémoz1,2, A. M. Siani2, G. R. Casale2, A. di Sarra3, B. Serpillo4, B. Petkov5, S. Scaglione3, A. Bonino6, S. Facta6, F. Fedele7, D. Grifoni8, L. Verdi9, and G. Zipoli8 H. Diémoz et al.
  • 1ARPA Valle d'Aosta, Loc. Grande Charrière 44, 11020 Saint-Christophe, Italy
  • 2Sapienza – Univ. Roma, Department of Physics, Piazzale Aldo Moro 5, 00185 Roma, Italy
  • 3ENEA, Via Anguillarese 301, 00123 S. Maria di Galeria, Roma, Italy
  • 4ARPA Basilicata, Via della Fisica 18 C/D, 85100 Potenza, Italy
  • 5CNR-ISAC, Via Gobetti 101, 40129 Bologna, Italy
  • 6ARPA Piemonte, Via Jervis 30, 10015 Ivrea, Italy
  • 7ARPA Puglia, Corso Trieste 27, 70126 Bari, Italy
  • 8CNR-IBIMET/LaMMa, Via Giovanni Caproni 8, 50145 Firenze, Italy
  • 9APPA Bolzano, Via Amba Alagi 5, 39100 Bolzano, Italy

Abstract. A blind intercomparison of ground-based ultraviolet (UV) instruments has been organized for the first time in Italy. The campaign was coordinated by the Environmental Protection Agency of Aosta Valley (ARPA Valle d'Aosta) and took place in Saint-Christophe (45.8° N, 7.4° E, 570 m a.s.l.), in the Alpine region, from 8 to 23 June 2010. It involved 8 institutions, 10 broadband radiometers, 2 filter radiometers and 2 spectroradiometers. Synchronized measurements of downward global solar UV irradiance at the ground were collected and the raw series were then individually processed by the respective operators on the base of their own procedures and calibration data. A radiative transfer model was successfully applied as an interpretative tool. The input parameters and output results are described in detail. The comparison was performed in terms of global solar UV Index and integrated UV-A irradiance against a well-calibrated double monochromator spectroradiometer as reference. An improved algorithm for comparing broadband data and spectra has been developed and is discussed in detail. For some instruments, we found average deviations ranging from −16 % up to 20 % relative to the reference and diurnal variations as large as 15 % even in clear days. Remarkable deviations were found for the instruments calibrated in the manufacturers' facilities and never involved in field intercomparison. Finally, some recommendations to the UV operators based on the campaign results are proposed.