TROPOMI/S5P total ozone column data: global ground-based validation and consistency with other satellite missions
Authors: Garane Katerina , Koukouli Maria-Elissavet , Verhoelst Tijl , Lerot Christophe , Heue Klaus-Peter , Fioletov Vitali , Balis Dimitrios , Bais Alkiviadis , Bazureau Ariane , Dehn Angelika , Goutail Florence , Granville Jose , Griffin Debora , Hubert Daan , Keppens Arno , Lambert Jean-Christopher , Loyola Diego , McLinden Chris , Pazmino Andrea , Pommereau Jean-Pierre , Redondas Alberto , Romahn Fabian , Valks Pieter , Van Roozendael Michel , Xu Jian , Zehner Claus , Zerefos Christos , Zimmer Walter 
Published: October 2019

Abstract. In October 2017, the Sentinel-5 Precursor (S5P) mission was launched,
carrying the TROPOspheric Monitoring Instrument (TROPOMI), which provides a
daily global coverage at a spatial resolution as high as 7 km × 3.5 km and
is expected to extend the European atmospheric composition record initiated
with GOME/ERS-2 in 1995, enhancing our scientific knowledge of atmospheric
processes with its unprecedented spatial resolution. Due to the ongoing need
to understand and monitor the recovery of the ozone layer, as well as the
evolution of tropospheric pollution, total ozone remains one of the leading
species of interest during this mission. In this work, the TROPOMI near real time (NRTI) and offline (OFFL) total
ozone column (TOC) products are presented and compared to daily ground-based
quality-assured Brewer and Dobson TOC measurements deposited in the World
Ozone and Ultraviolet Radiation Data Centre (WOUDC). Additional comparisons
to individual Brewer measurements from the Canadian Brewer Network and the
European Brewer Network (Eubrewnet) are performed. Furthermore, twilight
zenith-sky measurements obtained with ZSL-DOAS (Zenith Scattered Light
Differential Optical Absorption Spectroscopy) instruments, which form part of
the SAOZ network (Système d'Analyse par Observation Zénitale), are
used for the validation. The quality of the TROPOMI TOC data is evaluated in
terms of the influence of location, solar zenith angle, viewing angle, season,
effective temperature, surface albedo and clouds. For this purpose, globally
distributed ground-based measurements have been utilized as the background
truth. The overall statistical analysis of the global comparison shows that
the mean bias and the mean standard deviation of the percentage difference
between TROPOMI and ground-based TOC is within 0 –1.5 % and 2.5 %–4.5 %, respectively. The mean bias that results from the comparisons is
well within the S5P product requirements, while the mean standard deviation
is very close to those limits, especially considering that the statistics
shown here originate both from the satellite and the ground-based
measurements. Additionally, the TROPOMI OFFL and NRTI products are evaluated against
already known spaceborne sensors, namely, the Ozone Mapping Profiler Suite,
on board the Suomi National Polar-orbiting Partnership (OMPS/Suomi-NPP),
NASA v2 TOCs, and the Global Ozone Monitoring Experiment 2 (GOME-2), on
board the Metop-A (GOME-2/Metop-A) and Metop-B
(GOME-2/Metop-B) satellites. This analysis shows a very good agreement for
both TROPOMI products with well-established instruments, with the absolute
differences in mean bias and mean standard deviation being below +0.7 %
and 1 %, respectively. These results assure the scientific community of
the good quality of the TROPOMI TOC products during its first year of
operation and enhance the already prevalent expectation that TROPOMI/S5P will
play a very significant role in the continuity of ozone monitoring from
space.