ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-11619-2012 Evaluation of the new ESR network software for the retrieval of direct sun products from CIMEL CE318 and PREDE POM01 sun-sky radiometers Estellés V. 1 2 Campanelli M. 3 Smyth T. J. 4 Utrillas M. P. 1 Martínez-Lozano J. A. 1 Dept. Física de la Terra i Termodinàmica, Universitat de València, C/ Dr. Moliner 50, 46100 Burjassot, Spain Dept. Física Fundamental y Experimental, Electrónica y Sistemas, Universidad de La Laguna, Avda. Francisco Sánchez s/n, 38200 San Cristóbal de La Laguna, Santa Cruz de Tenerife, Spain Institute of Atmospheric Sciences and Climate, Italian National Research Council, Via Fosso del Cavaliere, Roma Tor Vergata, Italy Plymouth Marine Laboratory, Prospect Place, Plymouth PL1 3DH, UK 05 12 2012 12 23 11619 11630 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/11619/2012/acp-12-11619-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/11619/2012/acp-12-11619-2012.pdf

The European Skynet Radiometers network (EuroSkyRad or ESR) has been recently established as a research network of European PREDE sun-sky radiometers. Moreover, ESR is federated with SKYNET, an international network of PREDE sun-sky radiometers mostly present in East Asia. In contrast to SKYNET, the European network also integrates users of the CIMEL CE318 sky–sun photometer. Keeping instrumental duality in mind, a set of open source algorithms has been developed consisting of two modules for (1) the retrieval of direct sun products (aerosol optical depth, wavelength exponent and water vapor) from the sun extinction measurements; and (2) the inversion of the sky radiance to derive other aerosol optical properties such as size distribution, single scattering albedo or refractive index. In this study we evaluate the ESR direct sun products in comparison with the AERosol RObotic NETwork (AERONET) products. Specifically, we have applied the ESR algorithm to a CIMEL CE318 and PREDE POM simultaneously for a 4-yr database measured at the Burjassot site (Valencia, Spain), and compared the resultant products with the AERONET direct sun measurements obtained with the same CIMEL CE318 sky–sun photometer. The comparison shows that aerosol optical depth differences are mostly within the nominal uncertainty of 0.003 for a standard calibration instrument, and fall within the nominal AERONET uncertainty of 0.01–0.02 for a field instrument in the spectral range 340 to 1020 nm. In the cases of the Ångström exponent and the columnar water vapor, the differences are lower than 0.02 and 0.15 cm, respectively. Therefore, we present an open source code program that can be used with both CIMEL and PREDE sky radiometers and whose results are equivalent to AERONET and SKYNET retrievals.

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