1. MT Workshop - 17-20 October 2005 JUNE 2004 DECEMBER 2004 End of OCTOBER 2005 ? MAY 2002 ? Capabilities of multi-angle polarization cloud measurements from satellite : POLDER results POLDER and PARASOL are very similar instruments Frédéric Parol and the POLDER “ERB and Clouds”science team Laboratoire d ’Optique Atmosphérique / CNRS

2. MT Workshop - 17-20 October 2005 Outlines  Context and rationale : Cloud, radiation and climate  The POLDER instrument  Interests of multi-angle polarization measurements  Cloud properties  Earth radiation balance  POLDER “ERB,WV and Clouds” operational products  Conclusion and perspectives

3. MT Workshop - 17-20 October 2005 ~ -50Wm -2 in the SW ~ +30 Wm -2 in the LW Context and rationale : cloud, radiation and climate How clouds impact the Earth’s radiative energy balance Net cloud radiative forcing -20 W.m -2

4. MT Workshop - 17-20 October 2005 Change in the TOA Cloud Radiative Forcing associated with a CO 2 doubling is still uncertain Context and rationale : cloud, radiation and climate (IPCC 2001 ; from Le Treut and Mc Avaney, 2000) Effect of instantaneous CO 2 doubling Variation of emitted LW : 4 W.m -2 positive feedback : increases the warming negative feedback : reduces the warming

5. MT Workshop - 17-20 October 2005 Context and rationale : cloud, radiation and climate Small changes in clouds are potentially important for climate change “Probably the greatest uncertainty in future projections of climate arises from clouds and their interactions with radiation” (IPCC 2001) Clouds affect radiation through their height, their thickness and their radiative properties Satellite instruments allow for deriving and monitoring the radiation fluxes and/or the cloud properties (cloud cover, phase, temperature…) at the global scale

6. MT Workshop - 17-20 October 2005 POLDER concept and capabilities (POLarization and Directionality of the Earth’s Reflectances ) o POLDER instrument LOA/CNES o Japanese platforms Adeos 1 – Adeos 2 and CNES micro satellite Myriad platform o Missions o POLDER 1 : Nov 1997 – June 1997 o POLDER 2 : Jan 2003 – Oct 2003 o PARASOL : since Dec 2004 Main technical features Wide field of view lens ± 43° along track, ± 51° cross track  2400km x 1800km Filter wheel 8 spectral bands (443, 490, 565, 670, 763, 765, 865, 910 nm) + 1020nm for PARASOL Some are polarized CCD detector array 242 x 288 pixels  Spatial resolution - full resolution (~ 6x6 km 2 ) - coarse resolution [superpixel scale] (~ 20x20 km 2 )

7. MT Workshop - 17-20 October 2005 The multi-directional viewing capability of POLDER Up to 14  viewing angles per pixel for a single satellite pass France 97/01/13

8. MT Workshop - 17-20 October 2005 (A)Derivation of cloud properties from POLDER just two examples… Interests of the multiangle polarization measurements

9. MT Workshop - 17-20 October 2005 Multiangle polarisation measurements and Cloud Phase Variations of cloud polarized reflectance with scattering angle exhibits very different features depending on particle shapes (liquid droplets vs ice crystals). The cloud phase algorithm uses 4 major differences between these angular signatures. Riedi et al, GRL, 2000 140° 180° liquid ice

10. MT Workshop - 17-20 October 2005 Cloud thermodynamic phase from multiangle polarization

11. MT Workshop - 17-20 October 2005 Multiangle measurements : a tool for testing cloud (microphysical) models (1/3) Departure from the model are coded in spherical (or diffuse) albedo reflectances Optical thickness Spherical albedo

12. MT Workshop - 17-20 October 2005 Overcast conditions over ocean 0.01 - 0.05 0.25 - 0.300.10 - 0.15 0.15 - 0.20 0.20 - 0.25 0.05 - 0.01 0.30 - 0.35 0.35 - 0.40> 0.40 Liquid water clouds Scattering angle (deg.) Departure from the model Ice clouds 10µm-spheres Multiangle measurements : a tool for testing cloud microphysical models (2/3) What's happened when all clouds are assumed to be composed of spherical droplets ? Parol et al, IEEE, 1999 Doutriaux-Boucher et al, GRL, 2000

13. MT Workshop - 17-20 October 2005 Multiangle measurements : a tool for testing cloud microphysical models (3/3) The discrepancy observed for ice clouds decreases when the Inhomogeneous Hexagonal crystal Model (IHM) is used

14. MT Workshop - 17-20 October 2005 (B) Multiangle visible measurements : TOA SW albedo (and SW flux) retrievals Radiance (or reflectance) measurement Flux (or albedo) Theoretical ADM (RT calculations) Statistical ADM (observations) Interests of the multiangle polarization measurements

15. MT Workshop - 17-20 October 2005 Cloud optical thickness is retrieved under up to 14 directions Directional parameters (optical thickness and cloud albedo) are calculated at 443 nm (or 490nm), 670 nm and 865 nm. 1. The theoretical approach Multiangle multispectral measurements

16. MT Workshop - 17-20 October 2005 Multispectral integration : shortwave albedo = 443 nm  200 – 550 nm = 670 nm  550 – 700 nm = 865 nm  700 – 4000 nm SW ALBEDO 3 Spectral albedo

17. MT Workshop - 17-20 October 2005 Juin 2003 POLDER ALBEDO (x 100) POLDER-CERES differences, 20°S-20°N mean : -0,57 (-2,6%) Monthly mean shortwave albedo Viollier et al, GRL, 2002

18. MT Workshop - 17-20 October 2005 2. The statistical approach : ADMs based on satellite-derived cloud properties 0.50.70.91.11.3 (a) Optical Depth < 2.5 (b) Optical Depth 18-40 60 o 30 o 0o0o 60 o 30 o 0o0o 60 o  =0 o (fwd)  =0 o (fwd)  =180 o (bwd)  =180 o (bwd) R(  o, ,  ) Radiance measurement TOA flux R j (  0, ,  ) is the ADM for the scene type « j » (Loeb et al, JAS,2000)

19. MT Workshop - 17-20 October 2005 POLDER ERB,WV and Clouds Products Rapid overview of the different levels of operational cloud products

20. MT Workshop - 17-20 October 2005 Products availability POLDER1 : November 1996 to June 1997 POLDER2 : April 2003 to October 2004 PARASOL : since Dec 2004  Level1 : calibrated georeferenced data  Level2 : daily products – one file per orbit swath The level 2 (orbital swath) products contain about thirty non- directional parameters and ten directional parameters (for each of the 14 viewing directions)  Level3 : monthly global products The level 3 (monthly) products contain about forty parameters  Joint Atmosphere product (selected daily and monthly parameters) This product contains combined cloud and aerosol parameters Projection Lat-Lon 1080*2160 ( 1/6° ) HDF file format

21. MT Workshop - 17-20 October 2005 Data ordering interface from the CNES POLDER web portal... Web POLDER http://polder.cnes.fr

22. MT Workshop - 17-20 October 2005 Conclusion POLDER is a very nice research instrument with still no equivalent It provides : - Usual “standard” cloud parameters : ° Cloud cover, ° Cloud Optical thickness, ° Cloud pressure, ° etc…. - Original parameters : ° Cloud phase index ° Information on shape and size of cloud particles + Angular variability

23. MT Workshop - 17-20 October 2005 Conclusion/Perspectives Possible contribution of POLDER (and the A-train) to the MT mission : - to establish a climatology of cloud properties in the Tropics frequency of occurrence of liquid water clouds/ice clouds discrimination between thick cirrus and semi-transparent cirrus multiangle measurements could be analyzed in order to investigate regional variability of ice cloud particles others… - to evaluate the existing ADMs or/and to construct new ADMs based on multi-satellite-derived cloud properties - To be discussed with the ERB people (M. Viollier, …)