Showing papers by "Caroline Fayt published in 2009"

Six years of total ozone column measurements from SCIAMACHY nadir observations

Abstract: . Total O3 columns have been retrieved from six years of SCIAMACHY nadir UV radiance measurements using SDOAS, an adaptation of the GDOAS algorithm previously developed at BIRA-IASB for the GOME instrument. GDOAS and SDOAS have been implemented by the German Aerospace Center (DLR) in the version 4 of the GOME Data Processor (GDP) and in version 3 of the SCIAMACHY Ground Processor (SGP), respectively. The processors are being run at the DLR processing centre on behalf of the European Space Agency (ESA). We first focus on the description of the SDOAS algorithm with particular attention to the impact of uncertainties on the reference O3 absorption cross-sections. Second, the resulting SCIAMACHY total ozone data set is globally evaluated through large-scale comparisons with results from GOME and OMI as well as with ground-based correlative measurements. The various total ozone data sets are found to agree within 2% on average. However, a negative trend of 0.2–0.4%/year has been identified in the SCIAMACHY O3 columns; this probably originates from instrumental degradation effects that have not yet been fully characterized.

Multi-year comparison of stratospheric BrO vertical profiles retrieved from SCIAMACHY limb and ground-based UV-visible measurements

Abstract: . Vertical profiles of stratospheric bromine monoxide (BrO) retrieved daily from ENVISAT/SCIAMACHY (ENVIronmental SATellite/SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) limb scatter data and from ground-based UV-visible observations performed at Harestua (60° N, 11° E), Observatoire de Haute-Provence (44° N, 5.5° E), and Lauder (45° S, 170° E) are compared in the 15–27 km altitude range for the 2002–2006, 2005–2006, and 2002–2005 periods, respectively. At the three stations, the SCIAMACHY and ground-based UV-visible mean profiles agree reasonably well, with relative difference smaller than 23%. When comparing the BrO partial columns, the agreement obtained is good, with mean relative differences smaller than 11% and corresponding standard deviations in the 13–19% range. These comparison results are obtained, however, using different BrO cross sections in SCIAMACHY limb and ground-based UV-visible retrievals. The seasonal variation of the BrO columns at the three stations is consistently captured by both retrievals as well as large BrO column events occurring during the winter and early spring at Harestua which are associated with bromine activation.

Springtime Arctic ground-based spectroscopy of O 3 and related trace gases at Eureka, Canada – Part 1: Evaluation of the analysis method and comparison with infrared measurements

Abstract: . For the first time in spring 1999 the ground-based UV-visible zenith-sky measurements of stratospheric gases were performed at Environment Canada's Arctic Stratospheric Ozone Observatory (ASTRO) located at Eureka, Nunavut, Canada (80.05° N, 86.42° W, 610 m a.s.l.). The University of Toronto UV-visible ground-based spectrometer (UT-GBS) has been deployed for nine years afterwards at Eureka to measure ozone and NO2 total columns by using sunlight scattered from the zenith sky during spring, when the conditions leading to polar ozone depletion develop. During spring 2000, elevated OClO slant column densities were also measured for the first time. First dedicated analysis of UT-GBS measurements applying two independent differential optical absorption spectroscopy algorithms was performed on spectra recorded during spring 2000. The resulting ozone and NO2 total columns agreed to 4% and 5% or better, respectively. Also, first four years of UT-GBS results (1999–2003) were compared with those made by ozonesondes and by the Meteorogical Service of Canada Fourier transform infrared spectrometer (MSC FTS) at ASTRO, which has been operated by Canada's Department of Environment for measuring the total columns of several stratospheric gases. The comparison of UT-GBS and MSC FTS ozone total columns proved to be better than 5% for the periods when both instruments were viewing similar air masses.