SAFNWC/MSG Dust flag.

Transcription

1 SAFNWC/MSG Dust flag. Dust Week 1-5 March 2010 Hervé LE GLEAU, Marcel DERRIEN Centre de météorologie Spatiale. Lannion Météo-France 1

2 Plan SAFNWC context Dust flag in SAFNWC/MSG Cma product Algorithm description Validation Exemple of dust flag Exemple of application using dust flag 2

3 Plan SAFNWC context Dust flag in SAFNWC/MSG Cma product Algorithm description Validation Exemple of dust flag Exemple of application using dust flag 3

4 SAFNWC context -SAFNWC is a part of the Eumetsat ground segment -SAFNWC delivers software to process data from MSG and polar platforms (METOP/NOAA) registered users, including 29 European NMS and 3 SAFs (OSISAF, CMSAF, LSASAF) -SAFNWC/MSG SW includes three cloud products (CMa, CT, CTTH) developed by Météo-France/Lannion. A dust flag is part of CMa. -Detailed description of cloud algorithms and validation results available from -Daily synthesis of dust flag can be visualized on 4

5 Plan SAFNWC context Dust flag in SAFNWC/MSG Cma product Algorithm description Validation Exemple of dust flag Exemple of application using dust flag 5

6 Dust flag in SAFNWC/MSG CMa product CMa consist in two processes: The cloud detection which includes the following steps: Thresholding tests (applied to individual pixels in each slot): Channels differences are compared to thresholds which correspond to cloud free condition Thresholds are tabulated using RTTOV and 6S in clear sky conditions Atlas and NWP are used to describe surface and atmosphere Temporal and morphological analysis : to detect low clouds at day/night transition and thin fast moving clouds HRV analysis : to detect sub-pixel (ex: cumulus ) The dust detection which is applied to all pixels (cloudy and cloud 6

7 Dust flag in SAFNWC/MSG CMa product Main Cma output 1 Non-processed 2 Cloud-free 3 Cloud contaminated 4 Ccloud filled 5 Snow/ice contaminated 6 Undefined Quality Illumination/viewing geometry Availability of NWP input Availability of SEVIRI input Quality of CMa processing Dust flag: Volcanic plume flag Non processed Dust Not dust undefined Information on cloud detection successful tests 7

8 Plan SAFNWC context Dust flag in SAFNWC/MSG Cma product Algorithm description Validation Exemple of dust flag Exemple of application using dust flag 8

9 Daytime algorithm over land: spectral characteristics Dust Continental cloud free low clouds 9

10 Daytime algorithm over land: spectral characteristics Dust Continental cloud free low clouds 10

11 Daytime algorithm over land Daytime over land, dust detection is based on the thresholding of VIS0.6 m, NIR1.6 m, T10.8 m, T12.0 m, T8.7 m, T3.9 m as illustrated in previous slides To limit false alarm, addtional testing: -smooth in infrared and visible channel -not too cold and not too bright Dust detection needs illumination (T3.9 m, VIS0.6 m and NIR1.6 m) and thermal contrast (10.8 m and T12.0 m) -> performs worse at low sun elevation (morning/evening) 11

12 Daytime algorithm over sea: spectral characteristics Dust Continental cloud free low clouds 12

13 Daytime algorithm over sea: spectral characteristics Dust Continental cloud free low clouds 13

14 Daytime algorithm over sea Daytime over ocean, dust detection is based on the thresholding of VIS0.6 m, NIR1.6 m, T10.8 m, T12.0 m, T8.7 m as illustrated in previous slides To limit false alarm, addtional testing: -smooth in infrared and visible channel -not too cold and not too bright Dust detection needs illumination (VIS0.6 m and NIR1.6 m) and thermal contrast (10.8 m and T12.0 m): some events may be missed (if too warm) 14

15 Night-time algorithm over sea: spectral characteristics SDI=-0.20 SDI=0.6 A Saharan Dust Index is defined as: SDI= *(T39 m-t87 m) *(t108 m-t120 m) Large SDI indicates presence of dust. 15

16 Night-time algorithm over sea Night-time over ocean, dust detection is based on the thresholding of the Saharan Dust Index defined in previous slot. To limit false alarm, addtional testing: -smooth in infrared -not too cold -minimum rough value for T12.0 m-t10.8 m and T8.7 m-t10.8 m Note that the assumption is a dust layer colder than the back-ground - > the detection of warm low layer may be a problem 16

17 Plan SAFNWC context Dust flag in SAFNWC/MSG Cma product Algorithm description Validation Exemple of dust flag Exemple of application using dust flag 17

18 Validation with interactive target database (daytime) Dataset interactively gathered: small areas (5*5 pixels) -where a dust flag computed and -compared to label (cloud free, covered by dust or clouds) manually given by forecasters. POD dust = Not detected detected dust dust FAR dust = dust observed h m dust not observed fa cr Over ocean POD dust FAR dust v Over land POD dust FAR dust v h h+m fa fa+cr 18

19 Validation with aeronet (daytime) Comparison of dust flag daily synthesis with average aerosol optical thickness (aeronet network) 19

20 Validation with aeronet (daytime) 20

21 Validation with aeronet (daytime) 21

22 Coherency day-night dust flag over ocean Daytime dust flag Night-time dust flag 22

23 Coherency day-night dust flag over ocean Daytime dust flag Night-time dust flag Monthly SEVIRI dust flag over June

24 Plan SAFNWC context Dust flag in SAFNWC/MSG Cma product Algorithm description Validation Exemple of dust flag Exemple of application using dust flag 24

25 Example available on Eumetsat web image galery Illustration of coloured rain in Bulgaria 23 March h00UTC Eumetsat Dust RGB SEVIRI dust flag (in green) included in SEVIRI CT (usual colours) 25

26 Comparison with POLDER dust products Polder monthly averaged optical depth SEVIRI dust flag monthly synthesis 26

27 Comparison with POLDER dust products April 2008 April

28 Plan SAFNWC context Dust flag in SAFNWC/MSG Cma product Algorithm description Validation Exemple of dust flag Exemple of application using dust flag 28

29 Use at MF Support to Paris-Dakar race (now stopped!) Support to the elaboration of TEMSI: (forecasted map widely used for aeronautic purposes). dust flag used as an alert in conjonction with: observation, streched visible channel, RGBs 29

30 Use at MF Exemple of TEMSI 27 July h00TU 30

31 Use at MF 27 July h00TU 31

32 Use at MF 20 January h00TU 32