1 / 35

CMa & CT Cloud mask and type

This presentation provides an illustration of the algorithms used for the CMa & CT Cloud Mask and Type with MSG/SEVIRI. It includes examples of cloud types, known problems, and planned activities for 2004.

markpope
Download Presentation

CMa & CT Cloud mask and type

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CMa & CTCloud mask and type 15th June 2004 Madrid Hervé Le Gléau and Marcel Derrien Météo-France / CMS lannion

  2. Plan of CMa & CT presentation Illustration of algorithms’ basis with MSG/SEVIRI Algorithms’ very short description Some examples Known problems Planned activities in 2004

  3. As Meteosat-7

  4. As Meteosat-7 IR 10.8 mm 6th November 2003 05h00

  5. As Meteosat-7 VIS 0.6mm VIS 0.8mm 6th November 2003 09h00

  6. MSG/SEVIRI improvement for low clouds

  7. MSG/SEVIRI improvement for low clouds Low clouds T10.8mm – T3.9mm at night-time 6th November 2003 05h00

  8. MSG/SEVIRI improvement for low clouds Low clouds T3.9mm – T10.8mm at day-time 6th November 2003 09h00

  9. MSG/SEVIRI improvement for cirrus

  10. MSG/SEVIRI improvement for cirrus High semi-transparent clouds Low clouds T10.8mm – T3.9mm at night-time 6th November 2003 05h00

  11. MSG/SEVIRI improvement for cirrus High semi-transparent clouds Low clouds T8.7mm – T10.8mm 6th November 2003 05h00

  12. MSG/SEVIRI improvement for cirrus High semi-transparent clouds Low clouds T10.8mm – T12.0mm 6th November 2003 05h00

  13. MSG/SEVIRI improvement for snow

  14. MSG/SEVIRI improvement for snow Low clouds VIS 0.6mm Snow VIS 1.6mm 6th November 2003 09h00

  15. Cloud mask (CMa) categories

  16. Cloud type (CT) categories

  17. CMa algorithm • Clouds and snow are detected in each pixel of the image using multispectral theshold techiques : • Thresholds are computed using: • Atlas: height map • land/sea mask • Climatological maps: SST • continental visible reflectance • NWP short range forecast data: • surface temperature, • integrated atmospheric precipitable water • Most thresholds are tuned to radiometer’s spectral characteristics with Radiative Transfer Models in cloud free conditions (6S,RTTOV).

  18. CT algorithm • Cloudy pixels are classified according their radiative characteristics: • Semi-transparent and fractional clouds are distinguished from low/medium/high clouds using: • spectral features [T10.8mm-T12.0mm, T8.7mm-T10.8mm • T10.8mm-T3.9mm (night) or R0.6mm&T10.8mm (day)] • textural features [local variance of T10.8mm&R0.6mm (day)] • Low, medium and high clouds are then separated by comparing their T10.8mm to combination of NWP forecast temperature at various pressure levels [850, 700, 500 hPa and at tropopause levels]. • Separation between cumuliform & stratiform not performed. • Cloud phase flag not available

  19. Examples of cloud types Cloud types are displayed using colour palette available in hdf file: -First SEVIRI image 12th February 2003 13h30 -Low clouds/fog 5th February 2004 0h & 12h 6th November 2003 5h-9h -Convective clouds 28th July 2003 12h-16h -Snow 2nd March 2004 6h-12h

  20. Snow Low clouds High semi-transparent clouds 12 February 2003 13h30 VIS 0.6mm

  21. Snow Low clouds High semi-transparent clouds 12 February 2003 13h30 VIS 1.6mm

  22. Snow Low clouds High semi-transparent clouds 12 February 2003 13h30 T3.9mm - T10.8mm

  23. Snow Low clouds High semi-transparent clouds 12 February 2003 13h30 IR 10.8mm

  24. 12 February 2003 13h30 Cloud type

  25. Examples of low clouds/fog 5th february 2004 0h & 12h

  26. 5th February 2004 00h IR 10.8 mm T10.8mm – T3.9mm at night-time

  27. 5th February 2004 12h IR 10.8 mm VIS 0.6mm

  28. Examples of low clouds/fog: 6th November 2003 5h-9h

  29. Examples of convective clouds:28th July 2003 12h-16h

  30. Examples of snow:2nd March 2004 6h-12h

  31. Known problems CMa: -Low clouds may be missed at night-time or in case low solar elevation -Snow is not detected at night-time CT: -Very thin cirrus are classified as fractional -Low clouds may be classified as medium in case strong thermal inversion -Low clouds surmounted by cirrus may be classified as medium

  32. Planned activities in 2004 • Improvements to be included in SAFNWC (v1.2) • additional tuning where needed • Validation • cloud mask and type with SYNOP

More Related