Abstract
Abstract. This study aims to cross-validate ground-based and satellite-based models of three photobiological UV effective dose products: the Commission Internationale de l'Éclairage (CIE) erythemal UV, the production of vitamin D in the skin, and DNA damage, using high-temporal-resolution surface-based measurements of solar UV spectral irradiances from a synergy of instruments and models. The satellite-based Tropospheric Emission Monitoring Internet Service (TEMIS; version 1.4) UV daily dose data products were evaluated over the period 2009 to 2014 with ground-based data from a Norsk Institutt for Luftforskning (NILU)-UV multifilter radiometer located at the northern midlatitude super-site of the Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki (LAP/AUTh), in Greece. For the NILU-UV effective dose rates retrieval algorithm, a neural network (NN) was trained to learn the nonlinear functional relation between NILU-UV irradiances and collocated Brewer-based photobiological effective dose products. Then the algorithm was subjected to sensitivity analysis and validation. The correlation of the NN estimates with target outputs was high (r = 0. 988 to 0.990) and with a very low bias (0.000 to 0.011 in absolute units) proving the robustness of the NN algorithm. For further evaluation of the NILU NN-derived products, retrievals of the vitamin D and DNA-damage effective doses from a collocated Yankee Environmental Systems (YES) UVB-1 pyranometer were used. For cloud-free days, differences in the derived UV doses are better than 2 % for all UV dose products, revealing the reference quality of the ground-based UV doses at Thessaloniki from the NILU-UV NN retrievals. The TEMIS UV doses used in this study are derived from ozone measurements by the SCIAMACHY/Envisat and GOME2/MetOp-A satellite instruments, over the European domain in combination with SEVIRI/Meteosat-based diurnal cycle of the cloud cover fraction per 0. 5° × 0. 5° (lat × long) grid cells. TEMIS UV doses were found to be ∼ 12.5 % higher than the NILU NN estimates but, despite the presence of a visually apparent seasonal pattern, the R2 values were found to be robustly high and equal to 0.92–0.93 for 1588 all-sky coincidences. These results significantly improve when limiting the dataset to cloud-free days with differences of 0.57 % for the erythemal doses, 1.22 % for the vitamin D doses, and 1.18 % for the DNA-damage doses, with standard deviations of the order of 11–13 %. The improvement of the comparative statistics under cloud-free cases further testifies to the importance of the appropriate consideration of the contribution of clouds in the UV radiation reaching the Earth's surface. For the urban area of Thessaloniki, with highly variable aerosol, the weakness of the implicit aerosol information introduced to the TEMIS UV dose algorithm was revealed by comparison of the datasets to aerosol optical depths at 340 nm as reported by a collocated CIMEL sun photometer, operating in Thessaloniki at LAP/AUTh as part of the NASA Aerosol Robotic Network.
Highlights
During the last few decades, the danger of overexposure to solar UV radiation has been well analyzed and a causal link has been established to skin diseases and cancer since the mutation of DNA can be triggered by UV-B doses (Xiang et al, 2014; Parkin et al, 2011; Berwick et al, 2005; Setlow, 1974; among others)
Time series analysis and correlation statistics are performed on the daily UV dose for erythema, vitamin D, and DNA damage over a 6-year period (2009–2014)
Budget contributions relate, for example, to the uncertainty in the Brewer MKIII spectrophotometer with serial number #086 (B086) originally used spectra, the uncertainty caused by the application of the Norsk Institutt for Luftforskning (NILU)-UV neural network (NN) retrieval algorithm, the aerosol climatology assumed in the satellite-based algorithm and total ozone column retrieval errors
Summary
During the last few decades, the danger of overexposure to solar UV radiation has been well analyzed and a causal link has been established to skin diseases and cancer since the mutation of DNA can be triggered by UV-B doses (Xiang et al, 2014; Parkin et al, 2011; Berwick et al, 2005; Setlow, 1974; among others). As a result of advances in the fields of photobiology and groundbased measurements of UV using different types of instrumentation, a variety of methods exist to obtain erythemal, vitamin D, and DNA-damage dose rates (Kazantzidis et al, 2009; Webb and Engelsen, 2006; Pope et al, 2008; Engelsen et al, 2005; Samanek et al, 2006). Space technology has been making huge steps forward to monitor the Earth’s surface and atmosphere at higher spatial and temporal resolution and erythemal, vitamin D, and DNA-damage dose rates and doses can be retrieved globally from solar backscattered radiation observations from different satellite sensors. Long, reliable, and high-temporal-resolution ground-based estimates of surface photobiological effective dose quantities are of high importance in order to validate and characterize the satellite-derived UV products. Ozone layer depletion and recovery in times of climate change reinforce the need for establishing global long-term and quality-assured climate data records of the incident solar UV daily doses at the surface
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