Evaluated UVA Irradiances over a Twelve‐year Period at a Subtropical Site from Ozone Monitoring Instrument Data Including the Influence of Cloud

Abstract

This research investigated the influence of cloud on the broadband UVA solar noon irradiances evaluated from the solar noon satellite-based OMI spectral UV data that were compared to the irradiances of a ground-based radiometer from 1 October 2004 to 31 December 2016. The correlation between ground-based radiometer data and the evaluated OMI broadband UVA data evaluated with a model were dependent on whether or not the solar disk was obscured by the presence of cloud and the total sky cloud fraction. For conditions when the sun was not obscured by cloud, the evaluated satellite and the ground-based UVA irradiance correlation was best for cloud cover between 0 and 2 octa (R = 0.77) and the worst for high cloud cover of >4-8 octa (R between 0.3 and 0.4). The R reduced with increasing cloud amount and showed significantly weaker correlation when the sun was obscured. The correlation between the evaluated satellite broadband UVA and the ground-based measurements over the twelve years for total cloud cover conditions of 4 or less octa confirmed that the broadband UVA satellite evaluation model for the OMI spectral data is valid for approximately 71% of the days at the Southern Hemisphere subtropical study site.

Comparison of GOME‐2 UVA Satellite Data to Ground‐Based UVA Measurements in South Africa

“…Maximum and minimum annual values occurred during the austral summer and winter, respectively. The annual cycle of the daily dose and daily maximum irradiance was similar to other comparisons for sites in the Southern Hemisphere (24,23).…”

“…From previous comparison studies (24,35,17,23,36), it was found that GOME-2 data would overestimate surface UVA. We found that at Irene, De Aar and Upington, the GOME-2 data underestimated surface UVA measurements.…”

“…Amplified results were found for "Sun obscured" conditions where there was a low correlation (R 2 = 0.51, r = 0.71) of the satellite-derived UVA irradiance model with an increasing amount of cloud, as compared to "Sun not obscured" conditions. Overall, the study found that approximately 71% of the days in the 12-year period were accounted for by calibration of the satellite-derived UVA irradiances to surface measurements for most "Sun not obscured" conditions (24).…”

“…Results of all-sky conditions showed a positive bias in the GOME-2 satellite data where satellite daily exposure data and daily UVA satellite maximum irradiance data overpredicted surface measurements (23). Jebar et al (24) evaluated broadband UVA solar noon irradiances provided for a long-term data series over 12 years at a subtropical Southern Hemisphere site derived from the OMI satellite spectral UVA irradiances for sky conditions where clouds did not obscure the sun, "Sun not obscured," and where clouds obscured the sun, "Sun obscured." An inverse relationship was found between the amount of cloud cover and the correlation of ground-based and satellite data in "Sun not obscured" conditions.…”

SmartPDT®: Smartphone enabled real-time dosimetry via satellite observation for daylight photodynamic therapy

“…These multisource satellite data are fused, and a downscaling model is applied to achieve a temporal resolution of 1 min, a spatial resolution in the range 1-12 km depending on latitude. Using more than one satellite source as an input for clouds, ozone and aerosols allows the expansion of existing models [26][27][28][29] to the PpIX action spectrum and all weather conditions which is particularly important for climates with highly variable weather such as the UK. This model is further development of a previously reported method for the near real-time monitoring of erythema effective ultraviolet radiation [25].…”