2. SEMIANALYTICAL CLOUD RETRIEVAL ALGORITHM AND ITS APPLICATION TO DATA FROM MULTIPLE OPTICAL INSTRUMENTS ON SPACEBORNE PLATFORMS: SCIAMACHY, MERIS, MODIS, SeaWiFS AND GOME Alexander A. Kokhanovsky, Vladimir V. Rozanov Wolfgang von Hoyningen-Huene, John P. Burrows Institute of Remote Sensing, Bremen University P. O. Box 330440 Bremen, Germany alexk@iup.physik.uni-bremen.de

3. PARAMETERS to be retrieved: 1. Cloud optical thickness /5-100/ 2. Cloud top height /0.5-10km/ 3. Cloud cover /0-1/ 4. Cloud albedo/0.3-0.8/ 5. Liquid water path /50-200 / 6. Thermodynamic phase /ice, water or mixed clouds/ 7. Average size of droplets/crystals

4. PHYSICAL BASIS Bi-spectral measurement of TOA reflectance to get cloud optical thickness (visible), cloud droplet radius (IR) Spectrally resolved measurements (approximately, 50 spectral points in the oxygen A-band 758- 772nm) to get CTH, CBH The ratio R(1550)/R(1670) for the ice/water cloud discrimination

9. Exponential approximation

11. Table 1. Characteristics of selected space instruments, related to measurements of the backscattered light in the oxygen A-band (7550-7750 ). InstrumentPlatformYearSpectral interval, Spectral resolution, Spatial resolution, km 2 GOMEERS-219955760- 7940 3.340*320 SCIAMACHYENVISAT20026040- 8050 4.830*60 MERISENVISAT20027600 250.3*0.3 or 1.1*1.1 GLIADEOS-II20027630 80 0.25*0.25 and 1.0*1.0 POLDERADEOS-II20027633 7651 100 400 6.0*7.0

12. Typical SCIAMACHY spectra in the oxygen A-band Cloud top height determination from SCIAMACHY

13. WWW.IUP.PHYSIK.UNI-BREMEN.DE

15. VALIDATION MULTIPLE TECHNIQUES

19. Cloud top height determination from GOME data using oxygen A-band information as compared to ATSR-2 IR retrievals (ERS-2 satellite)

26. CONCLUSION SACURA has great potentials in cloud remote sensing

27. Acknowledgements K. Bramstedt, M. Buchwitz R. de Beek, K.-U. Eichmann W. Lotz, T. Nauss S. Noel, A. Rozanov H. Schroeter, M. Vountas European Space Agency DLR(grant 50EE0027) and NASA

28. The retrieval techniques 1: The look-up-table approach

29. 2: The semi-analytical approach

30. Optical characteristics of clouds Trishchenko and Liu, 2001 Number of cases Optical thickness ISCCP data Surface observations Kokhanovsky, 2003

31. The physics behind the semi-analytical approach SatelliteSun 1 2

32. The cloud optical thickness determination

33. The accuracy of the semi-analytical asymptotic theory

36. Cloud top height determination from a satellite The geometry of the problem

37. Nadir observation, solar zenith angle – 20 degrees Cloud optical thickness –20. The accuracy of the forward model Cloud top height determination from a satellite

38. The accuracy of the forward model Cloud top height determination from a satellite

39. The physical principle behind the retrieval

40. Preliminary results ! Cloud geometrical thickness determination from a satellite

41. Table 1. Characteristics of selected space instruments, related to measurements of the backscattered light in the oxygen A-band (7550-7750 ). InstrumentPlatformYearSpectral interval, Spectral resolution, Spatial resolution, km 2 GOMEERS-219955760- 7940 3.340*320 SCIAMACHYENVISAT20026040- 8050 4.830*60 MERISENVISAT20027600 250.3*0.3 or 1.1*1.1 GLIADEOS-II20027630 80 0.25*0.25 and 1.0*1.0 POLDERADEOS-II20027633 7651 100 400 6.0*7.0

42. Typical SCIAMACHY spectra in the oxygen A-band Cloud top height determination from SCIAMACHY

46. Cloud top height determination from GOME data using oxygen A-band information as compared to ATSR-2 IR retrievals (ERS-2 satellite)

53. Conclusions Most of important cloud parameters can be retrieved using spectral top of atmosphere reflectance measured by SCIAMACHY. The calibration of the instrument should be improved for this, however. Cases of inhomogeneous clouds can bias retrieval results considerably. This should be clarified in future research. The information on clouds obtained on a global and regional scale should enhance our studies of climate change, including anthropogenic influences on cloud microphysical and optical properties. JGR, 2003, 2004; IEEE TGRS, 2004; JQSRT, 2004; IEEE TGRS Letters, 2004

54. Acknowledgements K. Bramstedt, M. Buchwitz R. de Beek W. von Hoyningen-Huene S. Noel, M. Vountas ---- European Space Agency DLR(grant 50EE0027)