Progress of total ozone data retrieval from Phaeton - REG(AUTH) Alkis Bais, Fani Gkertsi, Theano Drosoglou, Natalia Kouremeti* Lab of Atmospheric Physics Aristotle University of Thessaloniki *PMOD/WRC Davos, Switzerland The European Metrology Research Programme (EMRP) is jointly funded by the EMRP participating countries within EURAMET and the European Union. ATMOZ Meeting, Prague29-30 October 2015 1
Layout Introduction to methodology for DOAS TOC retrieval Sensitivity tests on uncertainties arising from DOAS settings Comparisons with Brewer TOC data Outlook ATMOZ Meeting, Prague29-30 October 2015 2
DOAS data analysis Direct radiance spectra I(λ) are compared with a reference spectrum of unknown ozone slant column density (SCD REF ) in the DOAS equation: n I( ( )) offset( ) ln j( ) SCDj P( ) 0 I ( ) j 1 Effects of scattering (molecular and aerosol) are removed by fitting a loworder polynomial (P(λ)) Effects from n absorbers are included as products of cross-sections (σ j ) and SCD j : The differential slant column density (DSCD) of ozone is derived for each spectrum : DSCD SCD - SCD VCD * AMF - SCD i i REF i i REF Following the determination of SCD REF by Langley extrapolation, for each spectrum: DSCD i SCD REF VCDi TOCi AMF i ATMOZ Meeting, Prague29-30 October 2015 3
Distribution of errors in TOC retrieval Data before 19-6-2014 Data after 19-6-2014 ATMOZ Meeting, Prague29-30 October 2015 4
Uncertainties in TOC from DOAS retrieval Absorption cross sections of ozone Quality of the reference spectrum Spectral window of DOAS retrieval Raman scattering ( Ring effect ) Interferences from additional absorbers in the same spectral window ATMOZ Meeting, Prague29-30 October 2015 5
Standard DOAs analysis Spectral window: 310-337 nm Removal of broadband features with 3 rd degree polynomial Cross section O 3 : [Paur and Bass, 1984] @ 228 K Cross section NO 2 : [Vandaele et al., 1996] @ 298 K Cross section SO 2 : [Vandaele et al., 1994] @ 294 K Cross section HCHO: [Meller and Moortgat, 2000] @ 293K Ring effect Raman Scattering [Chance and Spurr, 1997] ATMOZ Meeting, Prague29-30 October 2015 6
Absorption cross-section dataset of ozone Reference: Alternative: Bass & Paur, [Paur and Bass, 1984], @ 228 K Burrows [Burrows et al., 1999], @ 221 K Bremen [Serdyuchenko et al., 2014], @ 223, 228, 233 K ATMOZ Meeting, Prague29-30 October 2015 7
Quality of the reference spectrum 31 May 2014 (DOY 151) for 18.7, 20.9, 25.1 SZA, Brewer Avg TOC ~368 DU 24 June 2014 (DOY 175) for 38.0, 40.0, 23.8 SZA, Brewer Avg TOC ~310 DU 30 June 2014 (DOY 181) for 25.2, 27.3, 29.4 SZA, Brewer Avg TOC ~305 DU ATMOZ Meeting, Prague29-30 October 2015 8
Quality of the reference spectrum Ideally, the Reference spectrum should correspond to zero absorption, affected only by solar Fraunhofer structures Quality of Reference spectrum depends on suitability of data/location for Langley extrapolation Careful selection of days/data may allow Langley extrapolations even at urban locations Tropospheric absorptions reduce the quality of Reference spectrum Radiance spectra with similar SCD with SCD ref have larger uncertainties, due to very small DSCD Reference spectra of low and high SCD may be combined to avoid small DSCD ATMOZ Meeting, Prague29-30 October 2015 9
Spectral window of DOAS retrieval Five ranges were investigated 305-330, 305-335, 310-337, 312-325 and 315-333 nm, showing large dependencies for the TOC retrieval (straylight effect at wavelengths shorter than ~310 nm?) Sensitivity restricted to ranges stating at wavelength longer than 315 nm: Start wavelength: 315, 316, 317.3, 318, 319.7, 321 nm End wavelength: 337 nm ATMOZ Meeting, Prague29-30 October 2015 10
Spectral window of DOAS retrieval ATMOZ Meeting, Prague29-30 October 2015 11
Spectral window of DOAS retrieval ATMOZ Meeting, Prague29-30 October 2015 12
Raman scattering ( Ring effect ) ATMOZ Meeting, Prague29-30 October 2015 13
Additional species (BrO, HONO, OClO) ATMOZ Meeting, Prague29-30 October 2015 14
Phaethon vs Brewer (El Arenosillio) ATMOZ Meeting, Prague29-30 October 2015 15
Phaethon vs Brewer El Arenosillio 27/5 5/6 2015 Thessaloniki Pre-campaign Post-campaign ATMOZ Meeting, Prague29-30 October 2015 16
Remarks The Phaethon-derived TOC shows higher noise compared to Brewer, which may arise from: Noise in the measured radiance spectra Non-linear response of the detector Missalignment of the optics Insufficient cloud screening Problems that have been encountered in the performance of the system (e.g., occasional irregular dark signal, reduction of sensitivity, distortion of spectral responsivity) Unexpected hardware problems in Brewer #005 during the campaign in Arenosillio, induced further uncertainties in the TOC derived from Brewer. So far data for 2014 have been analyzed in order to determine the sensitivity of the DOAS analysis ATMOZ Meeting, Prague29-30 October 2015 17
Outlook Development of filtering processes for Phaethon spectra to eliminate contamination from think clouds, miss-alignment of the optics, and level of signal Optimization of the DOAS settings by comparison with Brewer #005 in Thessaloniki Analysis of all available data 2014 - present ATMOZ Meeting, Prague29-30 October 2015 18
Thank you for your attention! ATMOZ Meeting, Prague29-30 October 2015 19