SCILOV10 FP MeetingSCIAMACHY irradiance validation

SCILOV10 FP, Frascati, 26/27 February, 2014

M. Weber and S.NoëlInstitute of Environmental Physics (IUP), University of Bremen (weber@uni-bremen.de)

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

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!

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

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

Past validation activities

• x

Skupin et al., 2005, Noel et al., 2007, Pagaran et al. 2011

SIM/SORCE 250-3000 2003-2010 Harder et al., (2010)

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

SCIAMACHY SSI V7 versus V8

Comparison to ATLAS-3 composite

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

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)

Correction w.r.t preflight

• Improves UV and NIR!

WLS lamp correction (inflight to preflight):

Changes from preflight

Fit range

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)