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APPLICATIONS OF METEOSAT SECOND GENERATION (MSG)

This article explores the optimum channel selection and enhancements for creating RGB image composites using Meteosat Second Generation (MSG) data. It covers topics such as channel selection based on physical properties, attribution of images to color beams, proper enhancement techniques, and final image enhancements.

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APPLICATIONS OF METEOSAT SECOND GENERATION (MSG)

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  1. APPLICATIONS OF METEOSAT SECOND GENERATION (MSG) RGB IMAGES: PART 03 CHANNEL SELECTION AND ENHANCEMENTS Author: Jochen Kerkmann (EUMETSAT) kerkmann@eumetsat.de Contributors: D. Rosenfeld (HUJ), HP. Roesli (MeteoSwiss) M. König (EUM)

  2. PART 3: CHANNEL SELECTION AND ENHANCEMENTS

  3. Channel Selection & Enhancements Optimum colouring of RGB image composites depends on: • I. Selection of the channels • Physical properties represented by the channels (e.g. IR10.8 provides cloud top temperature, VIS0.6 provides cloud optical thickness, VIS0.8 provides "greeness" of vegetation etc…) • II. Attribution of images to individual colour beams depends on: • Reproduction of RGB schemes inherited from other imagers; • Contrast and colours of the resulting RGB composite, which can be more or less pleasant (depending on personal view); • III. Proper enhancement of individual colour channels requires: • Conversion from radiances to brightness temperatures/reflectances; • Selection of display mode (inverted or not inverted); • Stretching of the intensity ranges (linear stretching of active dynamic range); • Gamma corection; • Gamma2 correction; • IV. Final enhancement • e.g. Gamma correction of final RGB image,

  4. I. (Cloud) Physical Properties representedby the MSG Channels VIS0.6: optical thickness and amount of cloud water and ice VIS0.8: optical thickness and amount of cloud water and ice "greeness" of vegetation NIR1.6, IR3.9r: particle size and phase WV6.2, WV7.3: mid- and upper level moisture IR8.7, IR10.8, IR12.0: top temperature IR8.7 - IR10.8: phase and optical thickness IR12.0 - IR10.8: optical thickness IR3.9 - IR10.8: optical thickness, phase, particle size IR13.4 - IR10.8: top height WV6.2 - IR10.8: top height, overshooting tops

  5. II.a RGB Schemes inhereted fromNOAA AVHRR The most popular RGB schemes used for NOAA AVHRR images are: RGB 1-2-4 (Day) RGB 1-3A-4 (Day) RGB 3B-4-5 (Day/Night) VIS0.6-VIS0.8-IR10.8 VIS0.6-NIR1.6-IR10.8 IR3.7-IR10.8-IR12.0 O. Hyvärinen, FMI, 2003

  6. II.a RGB Schemes inhereted from MODIS For MODIS (27 channels, not considering channels 8-16) there are 17550 different ways (this is 27!/(27-3)!) to choose 3 channels from 27 channels. Some popular RGB schemes used for MODIS images are: 01-04-03 (VIS0.6-VIS0.5-VIS0.4) 01-02-03 (VIS0.6-VIS0.8-VIS0.4) 01-06-31 (VIS0.6-NIR1.6-IR11.0) 26-06-31 (NIR1.3-NIR1.6-IR11.0) MODIS 5 March 2000 ?? UTC RGB Composite 01-04-03

  7. II.b Personal Choice/View RGB 01-02-03 RGB 03-02-01 gives bluish surface colours gives more "natural colours" MSG-1, 16 March 2004, 16:00 UTC

  8. II.b Personal Choice/View RGB 04r-02-09 RGB 02-04r-09 gives green Cb clouds gives better "warning colours" MSG-1, 5 May 2003, 13:30 UTC

  9. III.a Conversion from Radiances to Brightness Temperatures / Reflectances The best RGBs are achieved usingbrightness temperatures for IRand reflectances for VIS channels !!! • Counts  • Radiances  • Brightness temp. (IR channels)  • Reflectances (VIS channels) 

  10. III.a Conversion from Rad to BT / Refl. Example: MSG-1, 5 June 2003, 14:45 UTC, Channel 09 (IR10.8) Radiance Brightness Temperature Range = 14 / 115 mW/m2/sr/cm-1, =1.0 Range = 200 / 305 K, =1.0 better contrast !

  11. III.a Conversion from Rad to BT / Refl. Example: MSG-1, 5 June 2003, 14:45 UTC, Channel 02 (VIS0.8) Radiance Reflectance Range = 0 / 17 mW/m2/sr/cm-1, =1.0 Range = 0 / 100 %, =1.0 better contrast, no sun correction needed !

  12. III.a Conversion from Rad to BT / Refl. Example: MSG-1, 5 June 2003, 14:45 UTC, RGB 03-02-01 based on Radiances based on Reflectances better contrast, no sun correction needed ! no Gamma correction needed !

  13. III.a Conversion from Rad to BT / Refl. The relation between the SEVIRI radiances and the equivalent brightness temperatures / reflectances is described in a separate Powerpoint file (see conversion.ppt) !

  14. III.b Selection of Display Mode(Inverted or not Inverted) There are no general rules as regards the display mode (in particular for the IR channels). As described under II.a and II.b, it is a matter of traditions and personal view to select the display mode. Traditionally, for AVHRR RGB composites the IR channels are inverted. In this MSG Interpretation Guide, if not stated differently, all RGB composites are created from non-inverted (black = low energy, white = high energy) images.

  15. III.c Stretching of Intensity Ranges The range of interest for the MSG SEVIRI channels varies, depending on: • the phenomenon of interest (high clouds, low clouds, surface features, dust, smoke … ) • the season (winter, summer) • the time of the day (day / night / twilight)

  16. III.c Stretching of Intensity Ranges- Examples Overview- Feature Channel Total Range Range of Interest Cb Clouds Europe IR10.8 180 K / 340 K 203 K / 233 K Cb Clouds Africa IR10.8 180 K / 340 K 180 K / 220 K Dust Storm IR12.0-IR10.8 -15 K / +5 K -4 K / +2 K Dust Storm IR8.7-IR10.8 -15 K / +15 K -15 K / 0 K Fog Night IR3.9-IR10.8 -15 K / +25 K -10 K / 0 K Thin Cirrus IR8.7-IR10.8 -15 K / 15 K 0 K / +7 K

  17. III.c Stretching of Intensity Ranges- Example Cb Clouds Africa - Range = 180 K / 340 K, =1.0 Range = 180 K / 233 K, =1.0 MSG-1, 20 May 2003, 14:00 UTC, Channel 09 (IR10.8)

  18. III.c Stretching of Intensity Ranges- Example Cb Clouds Europe - Range = 180 K / 340 K, =1.0 Range = 203 K / 233 K, =1.0 MSG-1, 5 June 2003, 14:45 UTC, Channel 09 (IR10.8)

  19. III.c Stretching of Intensity Ranges- Example Dust Storm - Range = -15 K / +5 K, =1.0 Range = -4 K / +2 K, =1.0 MSG-1, 3 March 2004, 12:00 UTC, Diff. IR12.0 - IR10.8

  20. III.c Stretching of Intensity Ranges- Example Dust Storm - Range = -15 K / +15 K, =1.0 Range = -15 K / 0 K, =1.0 MSG-1, 3 March 2004, 12:00 UTC, Diff. IR8.7 - IR10.8

  21. III.c Stretching of Intensity Ranges- Example Fog at Night - Range = -15 K / +25 K, =1.0 Range = -10 K / 0 K, =1.0 MSG-1, 9 November 2003, 03:15 UTC, Diff. IR3.9 - IR10.8

  22. III.c Stretching of Intensity Ranges- Example Thin Cirrus - Range = -15 K / +15 K, =1.0 Range = 0 K / +7 K, =1.0 MSG-1, 25 June 2003, 10:00 UTC, Diff. IR8.7 - IR10.8

  23. III.d Gamma Correction In a nutshell, gamma correction changes the overall brightness (and color saturation) of an image as it is displayed on a monitor. The formula to perform a Gamma correction on a MSG IR (brightness temperature) image, within a range of BTmin and BTmax (see stretching of intensity ranges) is: where BRIT is the brightness intensity (0-255) of the displayed image. For Gamma < 1.0, the image is darkened, with the biggest effect happening for the dark (low input) pixel values. If Gamma > 1.0, the image is brightened overall, with the largest changes happening again for the dark shadows. The formula for the Gamma correction on a MSG VIS (reflectance) image is analog.

  24. III.d Gamma Correction Mapping function for different Gamma corrections

  25. III.d Gamma Correction: Examples Reflectance 0 20 40 60 80 100 BRIT (=1.0) 0 51 102 153 204 255 BRIT (=2.0) 0 114 161 197 228 255 BRIT (=0.5) 0 10 41 92 163 255 Examples of mapping functions for different Gamma corrections for displaying the reflectance (0 - 100%) for the MSG visible channels.

  26. III.d Gamma Correction: Examples Range = 0 - 100%, =0.5 Range = 0 - 100%, =1.0 Range = 0 - 100%, =2.0 MSG-1, 3 March 2004, 12:00 UTC, Channel 01 (VIS0.6)

  27. III.d Gamma Correction: Examples Click on the icon or on the image to see the animation (2805 KB) ! Left: Channel 01 (VIS0.6), various Gamma corrections (=1.0 … =5.0) Right: resulting RGB Composite 03,02,01

  28. III.e Gamma2 Correction The Gamma2 correction helps to enhance the middle part of the selected intensity range. This can be done e.g. with a tanh function. To be written

  29. IV. Final Enhancement To be written

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