Validation of the TROPOspheric Monitoring Instrument (TROPOMI) surface UV radiation product

Abstract

Abstract. The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite was launched on 13 October 2017 to provide the atmospheric composition for atmosphere and climate research. The S5P is a Sun-synchronous polar-orbiting satellite providing global daily coverage. The TROPOMI swath is 2600 km wide, and the ground resolution for most data products is 7.2×3.5 km2 (5.6×3.5 km2 since 6 August 2019) at nadir. The Finnish Meteorological Institute (FMI) is responsible for the development of the TROPOMI UV algorithm and the processing of the TROPOMI surface ultraviolet (UV) radiation product which includes 36 UV parameters in total. Ground-based data from 25 sites located in arctic, subarctic, temperate, equatorial and Antarctic areas were used for validation of the TROPOMI overpass irradiance at 305, 310, 324 and 380 nm, overpass erythemally weighted dose rate/UV index, and erythemally weighted daily dose for the period from 1 January 2018 to 31 August 2019. The validation results showed that for most sites 60 %–80 % of TROPOMI data was within ±20 % of ground-based data for snow-free surface conditions. The median relative differences to ground-based measurements of TROPOMI snow-free surface daily doses were within ±10 % and ±5 % at two-thirds and at half of the sites, respectively. At several sites more than 90 % of cloud-free TROPOMI data was within ±20 % of ground-based measurements. Generally median relative differences between TROPOMI data and ground-based measurements were a little biased towards negative values (i.e. satellite data < ground-based measurement), but at high latitudes where non-homogeneous topography and albedo or snow conditions occurred, the negative bias was exceptionally high: from −30 % to −65 %. Positive biases of 10 %–15 % were also found for mountainous sites due to challenging topography. The TROPOMI surface UV radiation product includes quality flags to detect increased uncertainties in the data due to heterogeneous surface albedo and rough terrain, which can be used to filter the data retrieved under challenging conditions.

GUV long-term measurements of total ozone column and effective cloud transmittance at three Norwegian sites

“…The choice of ozone profile in the calculations of N -value lookup tables is especially important for the winter when the SZA is large. Lapeta et al (2000) found that an inappropriate ozone profile may cause uncertainties up to 10 % in the retrieved TOC for SZA > 75 • . Sensitivity studies from Dahlback (1996) showed that the errors in total ozone, related to an inappropriate atmospheric profile in the RTM, were less than 1 % for SZA < 65 • .…”

“…The GUV instruments allow the calculation of the UV index, retrievals of total ozone column, cloud transmittance, and several other UV-related dose products (Dahlback, 1996;Høiskar et al, 2003;Bernhard et al, 2005). Data and dose products have been used in several international studies (Bernhard et al, 2013(Bernhard et al, , 2015Schmalwieser et al, 2017;Lakkala et al, 2020), and the data are available at https://github.com/uvnrpa (last access: 19 May 2021) and Johnsen et al (2020).…”

UV-Indien network: ground-based measurements dedicated to the monitoring of UV radiation over the western Indian Ocean

“…Data from the UV radiometers and the total sky imagers can be downloaded from Zenodo and are referenced at https://doi.org/10.5281/zenodo.4811488 (Lamy and Portafaix, 2021a).…”

Real-time UV index retrieval in Europe using Earth observation-based techniques: system description and quality assessment

“…Comparison of OMI surface UV irradiance estimates with ground-based measurements for Thessaloniki, Greece, showed that OMI irradiances overestimate surface observations for UVB wavelengths by between ∼ 1.5 % and 13.5 %, in contrast to underestimated satellite values for UVA wavelengths (Zempila et al, 2016). Results from the validation of the TROPOMI surface UV radiation product showed that most of the satellite data agreed within ±10 % with ground-based measurements for snow-free surfaces (Lakkala et al, 2020). Larger differences between satellite data and ground-based measurements were observed for sites with non-homogeneous topography and non-homogeneous surface albedo conditions.…”

“…There are many factors affecting UV irradiance reaching Earth's surface (Kerr and Fioletov, 2008). The dependence of UV irradiance on astronomical and geometrical parameters is generally well understood, and in many cases the changes are periodical (e.g., Blumthaler et al, 1997;Gröbner et al, 2017;Larkin et al, 2000;Seckmeyer et al, 2008). Atmospheric gases play a crucial role in attenuating UV irradiance; specifically, NO 2 is a major absorber in the UV (e.g., Cede et al, 2006), while O 3 is the main absorber at lower (UVB) wavelengths.…”