Rob Roebeling,

Hartwig Deneke and Arnout Feijt

GEWEX Cloud Assessment Meeting

Madison, United States of America

6 -7 July 2006

"METEOSAT-8 (SEVIRI) CLOUD PROPERTY RETRIEVALS

FOR CLIMATE STUDIES"

2

Introduction

Introduction

Validation for the CloudNet sites

Sensitivity

Norrkoping Cloud Work Shop results

Conclusions

3

Introduction

4

Retrieval Method

Project: Climate Monitoring SAF (CM-SAF)

Satellites: METEOSAT-8/SEVIRI and NOAA-17/AVHRR

Channels: VIS (0.63 m) and NIR (1.6 m) and IR (10.8 m)

Products: COT, CLWP, CPH (and Reff)

RTM: Doubling Adding KNMI model (DAK)

Surface reflectance: MODIS white sky albedo

Optical thicknesses: 0 -256

Water clouds: spherical droplets (1 -24 m)

Ice clouds: imperfect hexagonal crystals (6,12, 26, 51 m)

5

Examples Meteosat-8 Cloud Properties

Cloud Thermodynamic Phase

Water Ice Clear

Cloud Optical Thickness

6

Inter-calibration

NOAA-17/AVHRR&

METEOSAT-8/SEVIRI

7

Inter-Calibration: NOAA17 vs. METEOSAT-8

Diff. ~5% Diff. ~20%

SEVIRI vs. AVHRR reflectances using observations from

August – December 2004 over Central Africa.

8

Results after re-calibration

SEVIRI and AVHRR COT and CLWP after re-calibration to MODIS

using observations of April and May 2004 over Northern Europe.(SEVIRI: 0.6 m + 6% and 1.6 m +2%; AVHRR: 0.6 m + 6% and 1.6 m +22%)

Diff. 0- 5% Diff. 0- 5%

9

Validation

10

CloudNet Data

Cabauw

Paris

Chilbolton

Chilbolton

CLWP: 1 year of microwave radiometer

data at 2 CLOUDNET sites

COT: 1 year of pyranometer data, 27 stations

11

Comparison: Example CLWP product

SEVIRI CLWP 1 May 2004 CLWP time series from SEVIRI and microwave radiometer at Chilbolton, UK

12

CLWP Validation

Distribution of diff. LWP Meteosat-8 - MW, July 2004 (Chilbolton)

Distribution of Meteosat-8 LWP July 2004(Chilbolton)

13

CLWP Validation: Daily medians summer

Chilbolton, UK

14

CLWP Validation: Monthly medians summer

Chilbolton, UK

Palaiseau, France

15

CLWP Validation: Daily medians one year

Chilbolton, UK

16

CLWP Validation: Monthly medians one year

Chilbolton, UK

17

Validation Pyranometer

18

Sensitivity

19

Assessment error budget

Co-location & resolution (48 g m-2) Position ground station Parallax VIS – NIR mismatch Wobbling of the satellite Plane parallel assumption

MW – Radiometer (30 g. m-2)

Difference due to sampling different cloud portions (20 g m-2)

20

Assessment error budget

RT RT & FOV

FOV FOV

FOV

Total

21

Assessment error budget

222

2222

36~6070__

60~203048__

mgSumErrMSG

mgErrValTot

22

Sensitivity: viewing geometry6:00hr

0 = 70 = 83 7:00 hr

0 = 60 = 97 8:00 hr

0 = 51 = 110 9:00 hr

0 = 42 = 123

Fig. CLWP frequency distributions 21 June 2006 over Northern Europe

23

Sensitivity: viewing geometry

Loeb and Coakley, 1997, Journal of Climate

24

Conclusions

25

Conclusions (1)

Re-calibration reduces the differences between NOAA-17

and METEOSAT-8 retrievals of COT and CLWP over

Northern-Europe to about 5%.

There is good agreement between SEVIRI and microwave

radiometer retrieved cloud liquid water path.

The accuracy of SEVIRI CLWP retrievals decreases at solar

zenith angles > 60 degrees.

Accuracy changes due to geometry may manifest artificial

trends

26

Conclusions (2)

Part of the validation differences can be explain by co-

location and sampling differences.

The 15 minutes time resolution SEVIRI have enabled the

synergetic use of ground-based and satellite

observations.

27

Comparison Cloud Work Shop17 January 2006

28

Comparison CWS: Cloud Optical Thickness

29

Comparison CWS: Effective Radius

30

31

Methods: Radiative Transfer Modelling

R(sur)

Above the cloud

Below the cloud

ac

bc

Scattering and absorption

Reflectance,

Cloud properties

•Geometric thickness •Thermodynamic phase

•Optical thickness

•Effective radius

•Droplet distribution

Cloud properties

•Geometric thickness •Thermodynamic phase

•Optical thickness

•Effective radius

•Droplet distribution

32

Inter-calibration

NOAA-17/AVHRR&

METEOSAT-8/SEVIRI

33

Inter-Calibration: NOAA17 vs. METEOSAT-8

Diff. ~5% Diff. ~20%

SEVIRI vs. AVHRR reflectances using observations from

August – December 2004 over Central Africa.

34

Results after re-calibration

SEVIRI and AVHRR COT and CLWP after re-calibration to MODIS

using observations of April and May 2004 over Northern Europe.(SEVIRI: 0.6 m + 6% and 1.6 m +2%; AVHRR: 0.6 m + 6% and 1.6 m +22%)

Diff. 0- 5% Diff. 0- 5%

35

Sensitivity: viewing geometry

Fig. 0.6 m reflectance vs. viewing zenith angle

AVHRR MSG AVHRR MSG

36

Sensitivity: viewing geometry

Fig. 1.6m reflectance vs. viewing zenith angle

AVHRR MSG AVHRR MSG

37

Retrieval Method

Wate

r

Cloud

s

Ice

Cloud

s

38

Influence of reflectance spectra

SCIAMACHY reflectance spectra for 5 typical scenes (Stammes et al. 2005)

0

0.2

0.4

0.6

0.8

1

1450 1500 1550 1600 1650 1700 1750Wavelengths [nm]

Re

fle

cta

nc

e

Water CloudIce CloudVegetationOceanDesert

AVHRR SEVIRI

Diff. Ice clouds < 10%Diff. Water cloud < 3%

39

Monthly COT and CLWP compositesCOT Meteosat-8, May 2004

CLWP Meteosat-8, May 2004 CLWP NOAA-AVHRR, May 2004

COT NOAA-AVHRR, May 2004

40

CLWP Validation: Palaiseau daily results

41

Sensitivity: retrieval cloud optical thickness

Fig. 0.63 m reflectivities

Error in retrieved COT and Reff assuming errors of ± 1, 2 and 3%

Fig. 1.6 m reflectivities

42

Results using pre-launch calibration

Cum. freq. dist. COT for water clouds

Cum. freq. dist. CLWP for water clouds

SEVIRI > AVHRR

Diff. 0- 20% Diff. 10 - 20%

SEVIRI < AVHRR

43

Position station