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.
Highlights
The TROPOspheric Monitoring Instrument (TROPOMI) is a nadir-viewing imaging spectrometer measuring in the ultraviolet, visible, near-infrared and the shortwave infrared wavelengths onboard the Sentinel-5 Precursor (S5P) polarorbiting satellite
TROPOMI overpass irradiances were compared with the following spectroradiometers listed in Table 3: SOD, HEL, Villeneuve d’Ascq (VDA), DAV, DBR, AOS, OHP, ROM, THE, IZA, OPA, MEL and PAL
This is seen as a shift in ρ towards negative values when comparing the snow cover data set to the snow-free data set
Summary
The TROPOspheric Monitoring Instrument (TROPOMI) is a nadir-viewing imaging spectrometer measuring in the ultraviolet, visible, near-infrared and the shortwave infrared wavelengths onboard the Sentinel-5 Precursor (S5P) polarorbiting satellite. The S5P was launched on 13 October 2017 as part of the EU Copernicus programme to monitor atmospheric composition with a nominal lifetime of 7 years. The S5P is the first Copernicus mission dedicated to atmospheric observations, and it will be complemented by Sentinel 4 with geostationary orbit and Sentinel 5 on Sun-synchronous morning orbit with planned launches in the coming years. The TROPOMI level 2 data products include information of aerosols, carbon monoxide, clouds, formaldehyde, methane, nitrogen oxide, sulfur dioxide, ozone and surface ultraviolet (UV) radiation. Other products are generated within the Copernicus ground system, while the surface UV radiation is generated through the Finnish Sentinel collaborative ground segment
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