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Purpose
• To deepen your knowledge of satellite images' interpretation Preparation for the succeeding part about summer convection
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Pre-requesites
• Learning modules from EUMETSAT
• Online-presentation "Convection"
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Content
1. Physical background
2. Limitations
3. Monochromatic images- Colour tables
4. Highly sophisticated RGBs
5. Examples
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Physical background – brief repitition
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Solar and thermal radiation in relation to Meteosat channels and to absorption bands (talk by Marianne Koenig)
Wavelength (μm)
Thermal radiationsolar radiation
Absorption-bands
Ozone
Carbondioxide
Watervapour
W/m²/λ
Meteosat-channels (without HRV)
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Contribution Functions
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Influences to weighting functions
Klick upon the link below and try different combinations of– gas mixing ratio– line halfwidth– line strength– distance from the centre of the absorption band– scale height
(Tom Whittaker and Steve Ackermann)
http://cimss.ssec.wisc.edu/wxwise/class/aos340/spr00/WeightFun.html
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Technical background(channels)
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Meteosat -channels
• 12 channels (μm)– VIS/NIR: 0.6 / 0.8 /1.6– HRV: 0.5 – 1.1– WV: 6.2 / 7.3– IR: 3.8 / 8.7 / 10.8 / 12– Pseudo-Soundings: 9.7 / 13.4
• Horizontal resolution (Middle Europe)– HRV : 2 km– "others": 5 km
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Cloud amount (problems)
• Horizontal resolution: scattered Cu, Sc– HRV (first identification of convection's onset)– NOAA most suitable in Central Europe (however poor
temporal resolution problems for nowcasting)
• Contrast– VIS higher than IR
• Transparency (Ci, edges of Cb)– VIS underestimation of cloud amount
• Low clouds– IR (temperatures of cloud tops and the earth surface
similar) difficult to identify clouds (e.g., fog)
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Cloud top height
• most suitable: radiosoundings in a relevant area
• more reliable results– sharp and smooth cloud tops (e.g., St, Cb-anvil)
• less reliable results (yielding too low tops)– scattered cloudiness– thin Ci
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Meteosat-Product: Cloud top height
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Channels 1.6 and 3.9 μm
• (NIR 1.58 - 1.64 μm)– only during the day– snow/ice dark
Convective clouds with ice shield?
• (VIS/IR 3.55 - 3.93 μm)– day and night– during the night and in the case of small droplets „colder“– during the day CBs with small ice particles „warmer“
(IR+VIS defined according to IR-temperature) intense convection / updraft
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Meteosat: NIR 1.6 μm
Ice clouds - cirrus
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Meteosat: VIS/IR 3.9 μm (equalizing)
low clouds
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Meteosat: IR 10.8 μm (for comparison)
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NOAA (RGB+Kanal 3B): 30.05.97, 14:25
Characterisation of cloud top structures (overshooting tops, plumes) ofstorms over Spain and Portugal using the 3.9 mm channel on NOAA
AVHRR (M. Setvak, Czech NMS)
30 May 1997, 14.25 UTC, RGB image (ch. 1, 2, 4) 30 May 1997, 14.25 UTC, enhanced ch. 3 (3.9 mm)
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Analysis and diagnosis with coloured images
• purposes– better and simplified identification of relevant cloud
areas– specific analysis of critical thresholds
• two alternatives– colouring of monospectral images– composites (multi-spectral)
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Monospectral diagnosis (critical thresholds)
• definition of relevant thresholds icing (< 10°C) (depending among other in aircraft) probability of precipitation (< -10°C, in "warmer
regions") thunderstorms (<-25°C (summer, middle latitudes)) hail (<-55 to -60°C (summer, middle latitudes))
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Meteosat: IR 10.8 μm (enhanced)
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Channels within absorption bands
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Meteosat: Ozone-channel (IR: 9.38-9.94 IR: 9.38-9.94 μm)
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Meteosat: water vapour-channel (WV: 5.35-7.15 WV: 5.35-7.15 μm)("original")
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Enhancement: Limited range of counts
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Meteosat: water vapour-channel (WV: 5.35-7.15 WV: 5.35-7.15 μm)(equalizing)
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Meteosat: water vapour-channel (WV: 6.85-7.85 WV: 6.85-7.85 μm)(equalizing)
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Highly sophisticated MSG-interpretation
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EUMETSAT: Meteosat 8 (6,2 – 10,8) μm Overshootings?
09.06.2004, 07 UTC. (WV 6.2 μm minus IR 10.8 μm)V-structure (not quite clear) and WV 11.4 K warmer than IR (tip with the strongest updraft,round-shaped structures!)
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R = Difference WV6.2 - WV7.3G = Difference IR9.7 - IR10.8B = Channel WV6.2
THE "AIRMASS" RGB(Jochen Kerkmann, EUMETSAT (MSG-interpretation guide))
Applications:Applications: Rapid Cyclogenesis, Jet Stream Analysis, PV AnalysisArea:Area: Full MSG Viewing AreaTime:Time: Day and Night
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Airmass RGB Example(base: Jochen Kerkmann, EUMETSAT (MSG-interpretation guide))
6.2-7.3
9.7-10.8
6.2
In RGB (6.2-7.3/9.7-10.8/6.2) images, dry descending stratospheric air related to high PVappears in reddish colours !
The values shown above (in the red box) correspond tothe location (shown by an arrow) on the next slide !
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MSG-1, 7 January 2005, 22:00 UTC
Airmass RGB Example: high PV(base: Jochen Kerkmann, EUMETSAT (MSG-Interpretation guide))
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Differences and applications RGB "Severe convection" – only during day
(base: Jochen Kerkmann, EUMETSAT)
R: WV6.2 - WV7.3 overshooting tops
G: VIS/IR3.9 - IR10.8 optical thickness, phase,particle size, emissivity
B: NIR1.6 - VIS0.6 optical thickness, phase,particle size
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RGB 05-06,04-09,03-01 Example:Severe Convection (J. Kerkmann, EUMETSAT)
6.2 - 7.3
3.9 - 10.8
1.6 - 0.6
In RGB (6.2-7.3/ 3.9-10.8/1.6-0.6) images, cold Cb tops with small ice particlesappear in yellowish colours (Cbs with large ice particles appear in reddish colours) !
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New Convective
DevelopmentTop T. -65°C
MSG-1, 5 June 2003, 11:15 UTCRGB "Severe convection" WV6.2 - WV7.3 / IR3.9 - IR10.8 / NIR1.6 -
VIS0.8(from Jochen Kerkmann, EUMETSAT)