Methane distributions retrieved from IASI measurements

1. HYMN – Garmisch meeting, October 2008 Methane distributions retrieved from IASI measurements A. Razavi, C. Clerbaux, P-F. Coheur and D. Hurtmans

2. HYMN – Garmisch meeting, October 2008 Outline • Overview of IASI • Method for CH4 retrieval • Methane global distribution • Conclusion and perspective

3. HYMN – Garmisch meeting, October 2008 Overview of IASI Nadir looking FTS 12 km pixel x 4 @ nadir + scanning = ~ 48.3° Spectral coverage = 645-2760 cm-1 Spectral resolution = 0.5 cm-1 Radiometric noise ~ 0.25-0.5 K Timeline : • Oct. 19, 2006 MetOp-A launch  Nov. 29, 2006 First spectra • Jun. 4, 2007 L1C Operational dissemination (Eumetcast) • Sep. 27, 2007 L2 (P, T, clouds) operational dissimination • Mar. 1, 2008 L2 (trace gases) operational dissimination Up to 1.3 106 spectra/day (16Gb) [Clerbaux et al., 2007]

4. HYMN – Garmisch meeting, October 2008 IASI Spectra Thermal + reflected solar radiation (daytime) Measurements and products : • Climate: T, CO2, H2O, CH4 • Stratospheric Ozone: O3, HNO3 • Tropospheric Chemistry: O3 , CO, HNO3 + others • Operational applications : Pollution, fires, volcanoes, storms

5. HYMN – Garmisch meeting, October 2008 Outline • Overview of IASI • Method for CH4 retrieval • Methane global distribution • Conclusion and perspective

6. HYMN – Garmisch meeting, October 2008 Retrieval method Atmosphit (Research Mode) Constrained retrieval: Optimal Estimation theory measurement a priori information • profiles of any (IR absorbing) species • errors • averaging kernels [Coheur et al., 2005; Barret et al., 2005; Wespes et al., 2007; Herbin et al., 2007]

7. HYMN – Garmisch meeting, October 2008 CH4 retrieval regions ν4 band of CH4 completely covered some absorption lines of the ν3 band

8. HYMN – Garmisch meeting, October 2008 ν4 band of CH4 Interval chosen : 1240 - 1290 cm-1 Interfering species : H2O and N2O A priori temperature and humidity profiles from EumetCast L2 data

9. HYMN – Garmisch meeting, October 2008 ν4 band of CH4 Maximum sensitivity between 8 and 10 km

10. HYMN – Garmisch meeting, October 2008 ν3 band of CH4 Interval chosen : 2527 - 2760 cm-1 Interfering species : HDO and N2O New fitting parameter :  (slope of the baseline)

11. HYMN – Garmisch meeting, October 2008 ν3 band of CH4 Higher sensitivity from 0 to 6 km Improved information in the boundary layer

12. HYMN – Garmisch meeting, October 2008 Outline • Overview of IASI • Method for CH4 retrieval • Methane global distribution • Conclusion and perspective

13. HYMN – Garmisch meeting, October 2008 Global distribution 28th May 2008 • Using only the ν4 band of CH4 • Averaged on a 1° x 1° grid • Filters : - Cloud coverage (L2) <20% • - RMS lower than 4 x 10-6 W/(cm² sr m-1) • - errors lower than 1.5%

14. HYMN – Garmisch meeting, October 2008 Global distribution 28th May 2008 CH4 averaged column vmr CH4 averaged vmr over the N2O column (SCIAMACHY-like product)

15. HYMN – Garmisch meeting, October 2008 Water vapor correlation No apparent correlation But what drives these points down ?

16. HYMN – Garmisch meeting, October 2008 New covariance matrix From the LMDZ model : 4 days of 2004 a) with sa matrix variability : 3% b) With 15% variability Differences:

17. HYMN – Garmisch meeting, October 2008 Outline • Overview of IASI • Method for CH4 retrieval • Methane global distribution • Conclusion and perspective

18. HYMN – Garmisch meeting, October 2008 Conclusion and perspective • Improvement of the boundary layer sensitivity with the CH4ν3 band • First global distribution with IASI • Implementation of the new covariance matrix • Operational treatment using a “fast Atmosphit” based on look-up tables • Coupled inversions with the two spectral regions • Validation