Examination on total ozone column retrievals by Brewer spectrophotometry using different processing software
Abstract. The availability of long-term records of the total ozone content (TOC)
represents a valuable source of information for studies on the assessment of
short- and long-term atmospheric changes and their impact on the terrestrial
ecosystem. In particular, ground-based observations represent a valuable tool
for validating satellite-derived products. To our knowledge, details about
software packages for processing Brewer spectrophotometer measurements and
for retrieving the TOC are seldom specified in studies using such datasets. The
sources of the differences among retrieved TOCs from the Brewer instruments
located at the Italian stations of Rome and Aosta, using three freely available
codes (Brewer Processing Software, BPS; O3Brewer software; and European Brewer Network (EUBREWNET) level
1.5 products) are investigated here. Ground-based TOCs are also compared with
Ozone Monitoring Instrument (OMI) TOC retrievals used as an independent
dataset since no other instruments near the Brewer sites are available. The overall agreement of the BPS and O3Brewer TOC data with EUBREWNET data is
within the estimated total uncertainty in the retrieval of total ozone from a
Brewer spectrophotometer (1 %). However, differences can be found
depending on the software in use. Such differences become larger when the
instrumental sensitivity exhibits a fast and dramatic drift which can affect
the ozone retrievals significantly. Moreover, if daily mean values are
directly generated by the software, differences can be observed due to the
configuration set by the users to process single ozone measurement and the
rejection rules applied to data to calculate the daily value. This work aims to provide useful information both for scientists engaged in
ozone measurements with Brewer spectrophotometers and for stakeholders of
the Brewer data products available on Web-based platforms.