Cross-evaluation of GEMS tropospheric ozone retrieval performance using OMI data and the use of an ozonesonde dataset over East Asia for validation
Abstract. The Geostationary Environment Monitoring Spectrometer (GEMS) is scheduled to
be launched in 2019–2020 on board the GEO-KOMPSAT (GEOstationary KOrea
Multi-Purpose SATellite)-2B, contributing as the Asian partner of the global
geostationary constellation of air quality monitoring. To support this air
quality satellite mission, we perform a cross-evaluation of simulated GEMS
ozone profile retrievals from OMI (Ozone Monitoring Instrument) data based
on the optimal estimation and ozonesonde measurements within the GEMS
domain, covering from 5 ∘  S (Indonesia) to
45 ∘  N (south of the Russian border) and from
75 to 145 ∘  E. The comparison between
ozonesonde and GEMS shows a significant dependence on ozonesonde types.
Ozonesonde data measured by modified Brewer–Mast (MBM) at Trivandrum and
New Delhi show inconsistent seasonal variabilities in tropospheric ozone
compared to carbon–iodine (CI) and electrochemical condensation cell (ECC)
ozonesondes at other stations in a similar latitude regime. CI ozonesonde
measurements are negatively biased relative to ECC measurements by 2–4 DU;
better agreement is achieved when simulated GEMS ozone retrievals are
compared to ECC measurements. ECC ozone data at Hanoi, Kuala Lumpur, and
Singapore show abnormally worse agreements with simulated GEMS retrievals
than other ECC measurements. Therefore, ECC ozonesonde measurements at Hong
Kong, Pohang, Naha, Sapporo, and Tsukuba are finally identified as an
optimal reference dataset. The accuracy of simulated GEMS retrievals is
estimated to be ∼5.0  % for both tropospheric and
stratospheric column ozone with the precision of 15 % and 5 %, which
meets the GEMS ozone requirements.