Progress of total ozone data retrieval from Phaeton - REG(AUTH)

Transcription

1 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

2 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

3 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

4 Distribution of errors in TOC retrieval Data before Data after ATMOZ Meeting, Prague29-30 October

5 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

6 Standard DOAs analysis Spectral window: nm Removal of broadband features with 3 rd degree polynomial Cross section O 3 : [Paur and Bass, 228 K Cross section NO 2 : [Vandaele et al., 298 K Cross section SO 2 : [Vandaele et al., 294 K Cross section HCHO: [Meller and Moortgat, 293K Ring effect Raman Scattering [Chance and Spurr, 1997] ATMOZ Meeting, Prague29-30 October

7 Absorption cross-section dataset of ozone Reference: Alternative: Bass & Paur, [Paur and Bass, 228 K Burrows [Burrows et al., 221 K Bremen [Serdyuchenko et al., 223, 228, 233 K ATMOZ Meeting, Prague29-30 October

8 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

9 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

10 Spectral window of DOAS retrieval Five ranges were investigated , , , and 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

11 Spectral window of DOAS retrieval ATMOZ Meeting, Prague29-30 October

12 Spectral window of DOAS retrieval ATMOZ Meeting, Prague29-30 October

13 Raman scattering ( Ring effect ) ATMOZ Meeting, Prague29-30 October

14 Additional species (BrO, HONO, OClO) ATMOZ Meeting, Prague29-30 October

15 Phaethon vs Brewer (El Arenosillio) ATMOZ Meeting, Prague29-30 October

16 Phaethon vs Brewer El Arenosillio 27/5 5/ Thessaloniki Pre-campaign Post-campaign ATMOZ Meeting, Prague29-30 October

17 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

18 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 present ATMOZ Meeting, Prague29-30 October

19 Thank you for your attention! ATMOZ Meeting, Prague29-30 October