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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