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8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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André Szantai, P. Lopes, M. Desbois, A. Lahellec, G. Sèze
Laboratoire de Météorologie Dynamique
Palaiseau, France
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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Plan
1) New data : AMVs from EUMETSAT,
Trajectories (LMD method).
2) Comparison of different motion estimators : Qualitative comparisons
3) Prospects Quantitative results for comparisons - statistics.
Cloud classification (LMD method)
ECMWF analysed winds.
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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Atmospheric motion vectors (AMV)
EUMETSAT product, available every 3 hours (2:45,
5:45, 8:45UTC…)
1 file per instant with all channels (currently 3) : IR 10.8,
VIS 0.8 during daytime,
WV 6.2 cloud + WV 6.2 non cloudy areas.
Parameters : Position (longitude, latitude),
Wind speed and direction,
Pressure and corrected temperature.
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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Main differences between LMD motion vectors and EUMETSAT AMVs
AMVs repositioned on clouds (from original regular
grid) ==> irregular grid.
Calculation of a quality coefficient (QI).
Pressure level derived mainly from satellite data
(corrected brightness temperatures).
In some cases, 2 vectors can be found on the same
grid point and channel (with different quality
coefficients).
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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LMD motion vectors vs. EUMETSAT AMVs (VIS 0.8)
(low) 1000 - 925 - 850 - 700700 - 500 - 400 - 300 - 250 - 200 hPa (high) Best fit level (LMD) EUMETSAT pressure level (QI > 0.5)
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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AMVs in the WV 6.2 channel (mid- and high-level structures)
High-level cloud structures Quality indicator QI > 0.5 (both images)
Pure water vapour structures. Better tracking than in LMD
fields (esp. dry areas) Motion at 2 levels--------.
Pressure (hPa) 1000 925 850 700 500 400 300 250 200
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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Influence of the quality indicator (QI) of AMVsIR 10.8 image
QI = 0.5 More inconsistent vectors
QI = 0.8 Less dense vector groups
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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Cloud and atmospheric structure trajectories
Calculation method developed at LMD :
Extension of cloud motion vector calculation method
(block matching, minimization of the sum-of-squared
differences).
Similar quality tests applied along trajectories
Consistency tests detect the end of trajectories
(dissipation…) Variable number of vectors.
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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IR 10.8 cloud trajectories
IR 10.8 : Long living low level cloud trajectories, Medium-level trajectories (red, orange), High-level cloud trajectories (green, blue)
Maximal duration : 13 h 45.
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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WV 6.2 and WV 7.3 trajectories
WV 6.2 Numerous high-level cloud trajectories, Westward motion in bright (moist) pure WV
areas Few trajectories in very dry areas (bottom)
WV 7.3 More trajectories at medium-level, Different motion (medium-level) at
the edge of the pure WV structure (lower part).
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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Comparison of different motion estimators
Qualitative comparisons
Examined cases : vector fields from ULPGC
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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Vector field comparisons (VIS 0.8, NAtl, image 48)
LMD motion vectors More vectors in areas with complex
motion
ULPGC optical flow - correlation method
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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Remarks about the ULPGC vector fields(NAtl, VIS 0.8)
Closest fields with LMD motion vector fields (visually): 1) OF correlation vector field, 2) OF PDE vector field (smoother), 3) OF Structure Tensor vector field.
But statistics indicate : Larger differences for OF correlation
vector fields than for PDE fields.
Planned : Best-fit level for all fields Vectors expected at lower altitude :
bias > 0 ==>
(stronger winds at higher altitude)
LMDV > OFcorrV ⇒LMDP <
OFcorrP
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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Conclusions and prospects
Systematic comparisons (all motion vector fields) : Qualitative comparisons
Quantitative results - statistical parameters :
RMS vector difference, bias, NRMSVD, angular error.
With / without use of a cloud classification-based selection.
Use of complementary data : New cloud classification (LMD dynamical clustering-based)
method.
ECMWF analysed winds.
8/12/2005 FLUID Meeting Las Palmas (8-9 Dec. 2005)
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