Abstract
Abstract. 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.
Highlights
IntroductionThe aerosol radiative forcing uncertainty is larger (−0.6 ± 0.4 W m−2 for the direct effect) than the radiative forcing uncertainties due to greenhouse gases such as CO2 (1.8 ± 0.2 W m−2) (IPCC, 2007)
An accurate characterization of atmospheric aerosols is required to better quantify the Earth’s radiative balance and address issues such as climate change
We have applied the European Skynet Radiometers network (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 AERosol RObotic NETwork (AERONET) direct sun measurements obtained with the same CIMEL CE318 sky–sun photometer
Summary
The aerosol radiative forcing uncertainty is larger (−0.6 ± 0.4 W m−2 for the direct effect) than the radiative forcing uncertainties due to greenhouse gases such as CO2 (1.8 ± 0.2 W m−2) (IPCC, 2007). This uncertainty needs to be reduced to enable more accurate predictions of future climate states. The sun-sky radiometric technique is the most accurate and widely used. This technique consists of measuring two main variables at ground level: direct irradiance from the Sun, and diffuse radiance scattered from the sky. From the direct solar irradiance, an estimate of the aerosol optical depth (AOD) can be determined; this parameter can be considered the most simple parameter describing the aerosol burden in the atmospheric column
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