HCHO from MAXDOAS during CINDI: comparisons and use for satellite validation

1. HCHO from MAXDOAS during CINDI: comparisons and use for satellite validation G. Pinardi, I. De Smedt, K. Clémer, M. Van Roozendael, (BIRA-IASB) and data from: GIST, INTA, IUP-Bremen IUP-Heidelberg, JAMSTEC 11 March 2010, CINDI Workshop, BIRA, Brussels

2. Overview • HCHOfromMAXDOAS • overview of groups and of the retrievals settings • HCHO DSCD comparisons • HCHO VCD: geometrical approach and profiling • Comparison with satellite retrievals

3. Measurements Overview IUP-Heidelberg JAMSTEC BIRA GIST INTA IUP-Bremen • HCHO data from CINDI on the ftp last week:

4. Retrieval Settings Overview • HCHO retrieval settings: Proposition during the daily meetings and during the KNMI workshop  Did we agreed?

5. Retrieval Settings Overview

6. DSCD Comparison • HCHO DSCD comparisons: daily variations wrt elevation

7. DSCD Comparison • HCHO DSCD comparisons vs Bremen: correlations plots for each elev. BIRA

8. DSCD Comparison • HCHO DSCD comparisons vs Bremen: correlations plots for each elev. GIST

9. DSCD Comparison • HCHO DSCD comparisons vs Bremen: correlations plots for each elev. INTA

10. DSCD Comparison • HCHO DSCD comparisons vs Bremen: correlations plots for each elev. HEID.

11. DSCD Comparison • HCHO DSCD comparisons vs Bremen: correlations plots for each elev. JAMSTEC

12. DSCD Comparison • Overview regression analysis vs IUP-Bremen: How much of these differences are related to differences in the settings?

13. DSCD Comparison • Some other groups have HCHO DSCD (but not yet on the ftp): • Pandora: some HCHO showed yesterday by Alexander • MFDOAS: some HCHO analysis from Elena • NIWA: some HCHO analysis from Paul  see next few slides! • Who else? •  your input is welcomed to complete this first intercomparison!

14. Lauder CHOH using 90 deg spectrum at end of each elevation scan as reference for the whole scan

16. BLOCK YR DAY HRMN SC EHT SZA XS01 XS02 XS03 XS04 XS05 XS06 XS07 XS08 XS09 XS10 XS11 XS12 XS13 XS14 WScal Slope Resid Shift 00241 09 184 1045 51 014 31.16 0.57 6.93 -0.04 0.18 -0.22 -0.81 0.21 ***** 6.43 0.14 0.05 0.03 0.01 -0.06 -1.20 0.96 0.11 -0.52 0.46 0.55 0.02 0.03 0.04 0.01 0.06 ***** 0.19 0.02 0.00 0.00 0.01 0.01

17. Profiling tool: BePRO Profile inversion MAXDOAS measurement Radiative Transfer code LIDORT v3.3 MAXDOAS spectra 300-390 nm and 400-720nm 1°, 3°, 4°, 5°, 8°, 10°, 15°, 30°, and zenith parameters determining the atmosphere Pressure and temperature profiles Surface albedo Trace gas: cross-sections, VMR profiles Aerosol: optical properties (single scattering albedo, phase function, extinction profile) DOAS fitting O4 DSCDs O4 DSCDs + WF trace gas DSCDs trace gas DSCDs +WF Optimal Estimation 1 2 Aerosol extinction vertical profile Trace gas vertical profile

18. Profiling tool: BePRO

19. Profiling tool: BePRO

20. VCDtropo Comparison • HCHO VCDtropo comparisons: geom. approach VS BePRO Geom. approach: only points where column from 15° and 30° are within 40%

21. VCDtropo Comparison • HCHO VCDtropo comparisons: geom. approach VS BePRO In the current instrumental set-up and aerosol load: only 56% of geom. approach points selected as valid. Slightly higher AOD clouds

22. VCDtropo Comparison • HCHO VCDtropo comparisons: geom. approach VS BePRO • Morning: geom. approach underestimation • Evening: geom. approach overestimation hours Very few points

23. 2nd part: Comparison with the satellites

24. MAXDOAS-Satellite Comparison • Compare MAXDOAS (geom. approach) with the satellites: Direct comparison of satellite columns (c1) and MAX-DOAS total columns (c2): Relative diff. = (c1-c2)/c2.

25. MAXDOAS-Satellite Comparison • Compare MAXDOAS (BePRO) with the satellites: The MAX-DOAS total columns retrieved with BePro are larger than the geometrical approximation.  BePro provides the vertical profile (x2), the averaging kernel (A2) and the error estimate (that we can use to perform a more detailed comparison).

26. MAXDOAS-Satellite Comparison • Effect of the profile shape on the satellite AMF: Large impact of the a-priori profile shape AMF(xa1) = 1.25 AMF(x2) = 0.73 (AMF(x2) - AMF(xa1) / AMF(xa1)= = -41%

27. MAXDOAS-Satellite Comparison • Comparison tools (Rodgers and Connor, 2003):  The aim is to compare satellite total columns (c1, a1, xa1) with MAX-DOAS total columns (c2, a2, xa2) • Relation between the retrieved quantity and the true state x: • Adjustment for different a-priori using an arbitrary comparison ensemble xc for2 estimates of the total column: • Taking into account the differences in vertical sensitivity:

28. MAXDOAS-Satellite Comparison • Compare MAXDOAS (smoothed BePRO) with the satellites: For DOAS total column satellite retrievals of weak absorbers (Eskes and Boersma, 2003): ca1 = aT1xa1

29. Conclusion • HCHODSCDfromMAXDOAS: good agreement between the different groups, considering the remaining differences in the used settings.  we should focus more on that! • Different differences between the BIRA HCHO VCD from the geometrical approach and the profiling during the day; large different number of points (due to geometry). • Comparisons of the MAXDOAS HCHO “profile-columns” with the satellite retrievals • The shape of the a-priori profile is very important for the satellite AMF. • Very large improvement of the comparison when using the AK and a-priori information of both retrievals (smoothed comparisons).

30. Thank you…