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Volume 11, issue 1 | Copyright

Special issue: SKYNET – the international network for aerosol, clouds,...

Atmos. Meas. Tech., 11, 81-94, 2018
https://doi.org/10.5194/amt-11-81-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 Jan 2018

Research article | 09 Jan 2018

Precipitable water vapour content from ESR/SKYNET sun–sky radiometers: validation against GNSS/GPS and AERONET over three different sites in Europe

Monica Campanelli1, Alessandra Mascitelli1,2, Paolo Sanò1, Henri Diémoz3, Victor Estellés4, Stefano Federico1, Anna Maria Iannarelli5, Francesca Fratarcangeli2, Augusto Mazzoni2, Eugenio Realini6, Mattia Crespi2, Olivier Bock7, Jose A. Martínez-Lozano4, and Stefano Dietrich1 Monica Campanelli et al.
  • 1Institute of Atmospheric Sciences and Climate (ISAC), National Research Council (CNR), Via Fosso del Cavaliere 100, 00133 Rome, Italy
  • 2Geodesy and Geomatics Division – DICEA, University of Rome “La Sapienza”, via Eudossiana 18, 00184 Rome, Italy
  • 3Environmental Protection Agency (ARPA), Loc. Grande Charrière 44, 11020 Saint-Christophe, Aosta, Italy
  • 4Dept. Física de la Terra i Termodinàmica, Universitat de València, Burjassot, Valencia, Spain
  • 5SERCO SPA, Via Sciadonna 24, 00044 Frascati, Rome, Italy
  • 6Geomatics Research and Developments (GReD) srl, via Cavour 2, 22074 Lomazzo, CO, Italy
  • 7IGN LAREG, Univ. Paris Diderot, Sorbonne Paris Cité, 5 rue Thomas Mann, 75205 Paris CEDEX 13, France

Abstract. The estimation of the precipitable water vapour content (W) with high temporal and spatial resolution is of great interest to both meteorological and climatological studies. Several methodologies based on remote sensing techniques have been recently developed in order to obtain accurate and frequent measurements of this atmospheric parameter. Among them, the relative low cost and easy deployment of sun–sky radiometers, or sun photometers, operating in several international networks, allowed the development of automatic estimations of W from these instruments with high temporal resolution. However, the great problem of this methodology is the estimation of the sun-photometric calibration parameters. The objective of this paper is to validate a new methodology based on the hypothesis that the calibration parameters characterizing the atmospheric transmittance at 940nm are dependent on vertical profiles of temperature, air pressure and moisture typical of each measurement site. To obtain the calibration parameters some simultaneously seasonal measurements of W, from independent sources, taken over a large range of solar zenith angle and covering a wide range of W, are needed. In this work yearly GNSS/GPS datasets were used for obtaining a table of photometric calibration constants and the methodology was applied and validated in three European ESR-SKYNET network sites, characterized by different atmospheric and climatic conditions: Rome, Valencia and Aosta. Results were validated against the GNSS/GPS and AErosol RObotic NETwork (AERONET) W estimations. In both the validations the agreement was very high, with a percentage RMSD of about 6, 13 and 8% in the case of GPS intercomparison at Rome, Aosta and Valencia, respectively, and of 8% in the case of AERONET comparison in Valencia.

Analysing the results by W classes, the present methodology was found to clearly improve W estimation at low W content when compared against AERONET in terms of %bias, bringing the agreement with the GPS (considered the reference one) from a %bias of 5.76 to 0.52.

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The estimation of precipitable water vapour (W) content is of great interest in both meteorological and climatological studies. Sun photometers allowed the development of W automatic estimations with high temporal resolution. A new methodology, based on the hypothesis that the calibration parameters characterizing the atmospheric transmittance are dependent on vertical profiles of temperature, air pressure and moisture typical of each measurement site, has been presented providing good results.
The estimation of precipitable water vapour (W) content is of great interest in both...
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