1. GSICS meeting 5-8 March 2012, Beijing, China Slide: 1 Discussion Using GOME and SCIAMACHY as re- calibration reference for Visible and Near-Infrared channels Rob Roebeling Thanks to: Rűdiger Lang, Rose Munro, Yakov Livschitz, Richard Dyer, and Antoine Lacan

2. GSICS meeting 5-8 March 2012, Beijing, China Slide: 2 Content Introduction Results GOME-2 vs AVHRR Summary Pro’s and Con’s Discussion

3. GSICS meeting 5-8 March 2012, Beijing, China Slide: 3 MethodChannels (μm) Refl. Range (%) AvailabilityUpdate Freq.Errors (1σ) Sun-glint0.4–3.90-30TropicsDaily~4% inter-band DCC0.4–1.180-100TropicsMonthly2% LWC0.4–0.7, & 1.630-50YesMonthly4% Deserts0.4–1.225-45No (sel. areas)Monthly2-3% rel. Moon0.4–2.415Needs schedulingMonthly2-3% rel. 5% abs Ray- matching 0.4–3.90-100GlobalMonthly3% now 2% with SRF Rayleigh0.4–0.855-10Global (sel. oceans)Daily>2% Stars (abs)0-1?Needs navigationYearly??  All above figures currently under review  Strategy might be to combined methods Table : Summary of visible and near-infrared recalibration methods through intercalibration Visible and near-infrared re-calibration methods (GEO and LEO)

4. GSICS meeting 5-8 March 2012, Beijing, China Slide: 4 GOME-2 as a Reference Wavelength [nm] GOME-2 main channel transmittance I/I 0 Launch: Metop-A 10/2006 Orbit: Sun-synchronous, 09:30 Repeat cycle: 412 orbits (29 days) Coverage: Global 1.5 days Wavelengths: 240 nm to 800 nm Spectral resolution: 0.25 to 0. 5 nm (FWHM) Spatial resolution: -4 ch (40 x 80 km 2 ) with 4098 energy measurements -2 ch (40 x 10 km 2 ) with 512 energy measurements

5. GSICS meeting 5-8 March 2012, Beijing, China Slide: 5 Reflectivity ( (  /  0 )I/I 0 ) degradation until December 2010 Sahara – 745nm – relative to mean of 2007 Fig: Earthshine Sahara (Every 2 nd scanner angle position is shown) Preliminary Analysis!

6. GSICS meeting 5-8 March 2012, Beijing, China Slide: 6 SCIAMACHY as a Reference Operation Period: Since 1998 Radiometric: <4% Spatial Resolution: Limb vert. 3 x 132km, Nadir hor. 32 x 215km Swath Width: Limb and nadir mode: 1000km (max) Waveband UV-SWIR: 240-314,309-340,394-620,604-805,785-1050, 1000-1750,1940-2040,2265-2380 nm

7. GSICS meeting 5-8 March 2012, Beijing, China Slide: 7 GOME-2 Ch:3 (Band 5) 1024 measurements GOME-2 Ch:4 (Band 6) 1024 measurements AVHRR ch1 response function Inter-calibration - AVHRR/Metop-A using GOME-2

8. GSICS meeting 5-8 March 2012, Beijing, China Slide: 8 Inter-calibration - AVHRR/Metop-A using GOME-2 2007 2009 2011 AVHRR channel 1 to GOME-2 offset in reflectivity of ~9 to 10% (AVHRR < GOME-2) Preliminary results indicate that the offset has been quite stable during the last four years. see GSICS Quarterly Newsletters, vol 5, number 3, by B. Latter, RAL

9. GSICS meeting 5-8 March 2012, Beijing, China Slide: 9 Discussion & Conclusions I. Entire spectrum is resolved. When perfectly collocated the accuracy and precision are very high. II. GOME and GOME-2 record spans the period 1995- date III. GOME and GOME-2 suited for inter-calibration of the visible channels (0.6 and 0.8 micron IV. SCIAMACHY record spans the period 2002 –date V. SCIAMACHY suited for inter-calibration of the visible and shortwave infrared channels (0.6, 0.8, 1.6 and 2.1 micron) VI. Degradation issue (GOME-2 & SCIAMACHY ??) VII. Data provision needs to be coordinated with ESA VIII. Collocation and synchronisation might be more uncertain

10. GSICS meeting 5-8 March 2012, Beijing, China Slide: 10 Thank You Any Questions?

11. GSICS meeting 5-8 March 2012, Beijing, China Slide: 11 GOME-2 Ch:3 (Band 5) 1024 measurements GOME-2 Ch:4 (Band 6) 1024 measurements Seviri ch1 response function Inter-calibration – SEVIRI/MSG-2 using GOME-2 Preliminary results

12. GSICS meeting 5-8 March 2012, Beijing, China Slide: 12 Co-location of GOME-2 Metop-A with Seviri / MSG data. Spatial collocation: Average of all Seviri measurements (~4km) in one GOME-2 ground pixel (40 by 80 km) Temporal collocation: Within +- 7.5 min of sensing time. Inter-calibration – SEVIRI/MSG-2 using GOME-2 Preliminary results

13. GSICS meeting 5-8 March 2012, Beijing, China Slide: 13 More work needed!!! 1.Improve spatial co-location by taking spatial aliasing into account 2.Improved temporal co-location still possible at the expense of worse statistics 3.Filter for low variability, low path length difference, etc.. Inter-calibration – SEVIRI/MSG-2 using GOME-2 Preliminary results