1. SCILOV10 FP Meeting SCIAMACHY irradiance validation SCILOV10 FP, Frascati, 26/27 February, 2014 M. Weber and S.Noël Institute of Environmental Physics (IUP), University of Bremen (weber@uni-bremen.de)weber@uni-bremen.de

2. Overview SCIAMACHY calibration Past validation activities Comparison of SCIAMACHY V7 and V8 spectral solar irradiance (SSI) with Atlas-3 composite (considered a reference dataset) Recent results on NIR SSI (controversy) NOTE: – comparisons are done for SCIAMACHY data at the beginning of the mission (change from pre-flight condition) – timeseries information available from SOST web page (degradation monitoring) http://www.iup.uni-bremen.de/sciamachy/LTM/LTM.html

3. SCIAMACHY SSI 230-2400 nm, moderateley high spectral resolution (0.2-1.5 nm) Daily measurements available Preflight absolute radiometrically calibrated (TPD-TNO) using FEL lamps and NASA sphere, partially in thermal vacuum (not for all scan angles) Additional inflight calibration (Lichtenberg et al. 2006): – Straylight (inner-, intrachannel, spatial) – UV/VIS, Si detector, Ch. 1-5 memory effect dark current (leakage current, analog offset) – NIR channel, InGaAs detector, Ch. 6-8 non-linearity bad and dead pixels dark current (large thermal background) pixel-to-pixel gain Ice-layer (rapid throughput changes)  decontamination phases – Corrections to mirror surface polymerisation and other effects (degradation correction): WLS correction (Pagaran et al. 2011) Drawback: WLS degrades too! m-factor approach (Bramstedt et al. 2009)  V7 Optical throughput model with layer contamination (Krijger et al. 2014)  V8 Drawback, both assume constant sun!

4. Atlas-3 Composite SSI (Thuillier et al., 2004) Composite – 200-400 nm: SSBUV, SUSIM and SOLSPEC data from the ATLAS 1 and 3 (shuttle) missions, and SOLSTICE and SUSIM from UARS – 400-800 nm: SOLSPEC data – > 800 nm SOSP IR data Spectral resolution: 0.25-0.5 nm

5. Ballon LPMA/DOAS absolute radiometrically calibrated LPMA/DOAS at 32 km altitude above Aire-sur- l‘adour, Oct. 9, 2003 SSI ratios with respect to Kurucz Kitt Peak FTS Keydata update for V6 Gurlit et al., 2005

6. Past validation activities x Skupin et al., 2005, Noel et al., 2007, Pagaran et al. 2011 SIM/SORCE 250-30002003-2010Harder et al., (2010)

7. Few examples of past validation Comparison of V5 with WLS correction with SIM (Noel et al., 2007) Comparison of V6 with/without WLS correction with several other data (Pagaran et al., 2011) SCIAdata from April 2004

8. SCIAMACHY SSI V7 versus V8

9. Comparison to ATLAS-3 composite

10. Conclusion and Outlook SCIAMACHY agrees to within 3% with Atlas-3 in the visible (very similar to V7 and earlier comparisons) SCIAMACHY in V7 and V8 underestimate ATLAS-3 in the UV (3-10%), differences increase towards lower wavelengths SCIAMACHY V8 improves in the overlap regions Ch. 3/4 and 4/5 and near 350 nm, but also produces features (near 850 nm, > 1500 nm) both m-factors (Bramstedt et al., 2009) and optical throughput model (Krijger et al. 2014) do not account for natural solar variability (solar cycle, 27-day solar rotation) which is probably ok for trace gas and cloud/aerosol atmospheric retrievals

11. Recommendations Still some issues with NIR channels in V8 (quick icing a problem, 850 nm)  needs further evaluation Specific solar data products for space and solar science communities (no removals of natural variability) in addition to V8 data Improving degradation (optical throughput model) by allowing for natural SSI variability (EU Solid, BMBF ROMIC) Corrections from pre-flight condition is still not complete (check on etalon corrections)

12. Correction w.r.t preflight Improves UV and NIR! WLS lamp correction (inflight to preflight): Changes from preflight Fit range

13. Some hot topics: NIR SSI Bolsee et al., Sol. Phys., 2014 NIR SSI lower by 8% (>1600 nm) w.r.t. ATLAS-3 and SIM SCIAMACHY in agreement with ground data (IRSPERAD) and ISS SOLAR/SOLSPEC Using WLS correction also good agreement in Channels 7/8 with SOLAR/SOLSPEC on ISS (Thuillier et al., 2013)