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SCOPE-NWC, Geneva, 19-22 November 2013
IR10.8 IR10.8-IR12.0Meteosat-9, 201004015, 14:00 UTCSlide: 3
SEVIRI Ash Detection - Example
SCOPE-NWC, Geneva, 19-22 November 2013
SEVIRI Ash Detection
Simple test on brightness temperature difference:
BTD := T10.8 – T12.0 < 0. K
Many false alarms• over clear land at night• over cloud edgesi.e. "simple" detection is faced with many false alarms- Additional channel tests were introduced
Slide: 4
SCOPE-NWC, Geneva, 19-22 November 2013
IR10.8-IR12.0 Ash detection Prata v1Meteosat-9, 201004015, 14:00 UTCSlide: 5
SEVIRI Ash Detection: Simple BTD Test
SCOPE-NWC, Geneva, 19-22 November 2013Slide: 6
SEVIRI Ash Detection: Less False Alarms
IR10.8-IR12.0 Ash detection v2010Meteosat-9, 201004015, 14:00 UTC
SCOPE-NWC, Geneva, 19-22 November 2013
For Detected Ash: Retrieval of Quantitative Information
(following scientific collaboration with Dr. Fred Prata, NILU)
Slide: 7
Background:
Retrieval of effective particle size and optical depth as a function of the BTD difference IR10.8 – IR12.0 (and some other parameters) , from pre-defined lookup-tables (computed using a given spectroscopic dataset).
Combining the size and optical depth gives the total mass loading as the final product.
Note:
“Thick” ash clouds cannot be discriminated from opaque water/ice clouds!
SCOPE-NWC, Geneva, 19-22 November 2013Slide: 9
Corresponds to mass loading of
~ 0.4 g/m2
SEVIRI Ash Retrieval - Validation
SCOPE-NWC, Geneva, 19-22 November 2013Slide: 10
Corresponds to mass loading of
~ 0.2 g/m2
SEVIRI Ash Retrieval - Validation
SCOPE-NWC, Geneva, 19-22 November 2013Slide: 11
Additional information on ash cloud thickness was used to turn MSG total mass loadings into concentrations:
Very good agreement found in this case (assumption is that concentration is vertically homogeneous)
SEVIRI Ash Retrieval - Validation
SCOPE-NWC, Geneva, 19-22 November 2013Slide: 12
0.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0
Mass loading (g m-2)
0.20.2 0.2
0.2
0.2
0.2
2.0
2.0
Date:2010.05.17 16:15 UT
-3 -2 -1 0 1 2 3 4 5 6 7
52
53
54
55
56
London
Amsterdam
Glasgow
Manchester
Track 1
Track 2
Track 3
Track 4
Track 5
1.6 1.8 2.0 2.2 2.4Longitude (o)
0.0
0.2
0.4
0.6
0.8
Con
cent
ratio
n (m
g m
-3)
SEVIRI
Less good agreement found in this case – but note:
These are very low concentrations!
SEVIRI Ash Retrieval - Validation
SCOPE-NWC, Geneva, 19-22 November 2013Slide: 13
SEVIRI can derive total mass loading, and with additional information on ash cloud thickness (models, other measurements), this can be turned into mass concentrations.
SEVIRI can thus derive ash concentrations over the entire range of interest
Very thick ash is not detected
Ash below thick clouds is not detected
Reliable detection remains a problem
SEVIRI Ash Retrieval - Validation
SCOPE-NWC, Geneva, 19-22 November 2013
SEVIRI Volcanic Ash Product
The ash product is available in the following formats:
•netCDF format (with ash effective radius, mass loading, height (incl. quality) per pixel) – 96 times per dayand in case of an event (upon request from the London VAAC):•CAP (Common Alert Protocol) format •Text files•Image (PNG format)Access restricted to National Meteorological Services of the EUMETSAT Member States and the London and Toulouse VAAC
Slide: 14
SCOPE-NWC, Geneva, 19-22 November 2013
Word of Caution
No full validation of the operational product done yet – satellite product should always be used in combination with other information!
Example: Combination with “visual” impression from the RGB composites, e.g. the RGB colour composites
IR12.0 – IR10.8IR10.8 - IR8.7 IR10.8
Slide: 15
SCOPE-NWC, Geneva, 19-22 November 2013Slide: 17
SEVIRI Ash DetectionFuture Plans
• Reliable ash detection still a problem
• Improvements and tests are ongoing
• Plans to investigate all volcanic eruptions in the Meteosat FOV: science study commissioned with the Met Office in Nov 2013
• Use of two Meteosats (or Meteosat and a LEO satellite) for stereo height assignment – science study to be commissioned end of 2013
• Explore potential of an optimal estimation approach (promising especially in case of ash above lower clouds) – science study commissioned with RAL in Nov 2013 (also baseline for MTG);OE approach: fitting radiances of all channels to find best solution for ash properties, notably also height
SCOPE-NWC, Geneva, 19-22 November 2013
International Collaboration
CGMS resolution at its 40th meeting (2012):
”EUMETSAT, JMA and NOAA are invited to report on their development toward common and consistent volcanic ash products from Meteosat and MTSAT-2 and GOES, respectively.“
JMA and KMA have received a copy of our prototype code (following the Prata algorithm) and will make the product operationally available for MTSAT and COMS, in order to have a globally consistent product
Slide: 19
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