The empirically corrected EP-TOMS total ozone data against Brewer measurements at El Arenosillo (Southwestern Spain)

Abstract—This paper focuses on the validation of the empirically
corrected total ozone column (TOC) data provided by the
Earth Probe Total Ozone Mapping Spectrometer (EP-TOMS) using
ground-based measurements recorded by a well-calibrated
Brewer spectroradiometer located at El Arenosillo (Spain). In
addition, satellite TOC observations derived from the OzoneMonitoring
Instrument (OMI) with the TOMS algorithm are also used
in this paper. The agreement between EP-TOMS TOC data and
Brewer measurements is excellent (R2 ∼ 0.92) even for the period
2000–2005 when a higher EP-TOMS instrument degradation
occurred. Despite its low magnitude, the EP-TOMS–Brewer relative
differences depend on the solar zenith angle (SZA), showing
a clear seasonal cycle with amplitude between ±2% and ±4%.
Conversely, OMI–Brewer relative differences show a constant
negative value around −1% with no significant dependence on
SZA. No significant dependence on the ground-based to satellitebased
differences with respect to the EP-TOMS scene or to the
OMI crosstrack position is observed for either satellite retrieval
algorithm. Finally, TOC, estimated by the two satellite instruments,
have also been compared, showing a good agreement
(R2 ∼ 0.88). Overall, we conclude that the empirical correction
of the EP-TOMS data record provides a reprocessed set of high
quality. However, EP-TOMS data after year 2000 should not be
used in calculations of global-ozone trending due to remaining
errors in the data set and because it is no longer an independent
data set.
Index Terms—Aircraft instrumentation, algorithms, ozone,
ultraviolet (UV) radiometry.