traditional‘ satellite methods (clouds are bright) • what...

Satellite Satellite Group:Group:http://satellitehttp://satellite..iupiup..uniuni--heidelbergheidelberg.de.de

Institut fInstitut füür Umweltphysikr UmweltphysikUniversity of HeidelbergUniversity of Heidelberg

thomasthomas..wagnerwagner@@iupiup..uniuni--heidelbergheidelberg.de.deFrascati, May 2006Frascati, May 2006

Probing internal cloud properties from spaceThomas Wagner, Steffen Beirle, Tim Deutschmann, Michael

Grzegorski, Suniti Sanghavi, Ulrich Platt

Institut für Umweltphysik, University of Heidelberg, Germany

• ‚Traditional‘ satellite methods (clouds are bright...)

• What can new satellite observations offer? (spectral measurements)

• Model results & measurements of O4 & O2 absorption and Ring effect

• Conclusions & outlook




Early satellite remote sensing of clouds: Images taken from space

First image of the earth

Tiros 1 1960

Tiros IX, 1965




Measurements of radiometers: Cloud images

0.58-0.68µm 1.58 - 1.64µm

AVHRR, chan. 1

29 Apr 2006 at 1330 UTC

Dundee Satellite Receiving Station (http://www.sat.dundee.ac.uk)

AVHRR, chan. 3Radiance

dependends on optical depth

and particle size

Usually clouds are bright and whiteExceptions: smoke clouds, aerosols

Visible Near IR

© MODIS algorithm document





AVHRR, chan. 1

29 Apr 2006 at 1330 UTCAVHRR, chan. 3 AVHRR, chan. 4 SSM/I

0.58-0.68µm 1.58 - 1.64µm 10.3 - 11.3µm 0.8 - 1.5 cm

Visible Near IR Thermal IR Microwave: liquid water

Dundee Satellite Receiving Station (http://www.sat.dundee.ac.uk)Remote sensing systems (http://www.ssmi.com/)





AVHRR, chan. 1

29 Apr 2006 at 1330 UTCAVHRR, chan. 3 AVHRR, chan. 4 SSM/I

Many cloud parameters can be retrieved from radiometers:

Cloud fraction, Optical depth, Cloud top height, Droplet size, Thermodynamical state, Liquid water path, etc....

0.58-0.68µm 1.58 - 1.64µm 10.3 - 11.3µm 0.8 - 1.5 cm

Visible Near IR Thermal IR Microwave liquid water

Dundee Satellite Receiving Station (http://www.sat.dundee.ac.uk)Remote sensing systems (http://www.ssmi.com/)




GOME & SCIA spectral propertiesO3 UV

O3 vis

HCHO

OClO

O4

O2

H2O

SO2 NO2 BrO

Satellite group: http://satellite.iup.uni-heidelberg.de

Set of Atmospheric Absorbers Identified in GOME Spectra at the Satellite Group at the Institut für Umweltphysik

0.0

0.2

0.4

0.6

300 400 500 600 700 800Wavelength [nm]

Spec

tral a

lbed

o

Spectra also from:

SCIAMACHY, OMI, GOME-II, etc….

What additional information can be expected from spectral measurements? (e.g. GOME)




GOME & SCIA spectral propertiesO3 UV

O3 vis

HCHO

OClO

O4

O2

H2O

SO2 NO2 BrO

Satellite group: http://satellite.iup.uni-heidelberg.de

Set of Atmospheric Absorbers Identified in GOME Spectra at the Satellite Group at the Institut für Umweltphysik

0.0

0.2

0.4

0.6

300 400 500 600 700 800Wavelength [nm]

Spec

tral a

lbed

o

Both, trace gas absorptions and Ring effect (Raman scattering) are affected by modifications of the atmospheric light path, especially due to clouds.

=> They can serve as Light path tracers

What additional information can be expected from spectral measurements? (e.g. GOME)



thomasthomas..wagnerwagner@@iupiup..uniuni--heidelbergheidelberg.de.deFrascatiFrascati, May 2006, May 2006




Which trace gases are well suited as Light Path Tracer?

• Concentration should be constant and known (e.g. from independent measurements)






• Absorption should be strong enough for a good signal to noise ratio, but weak enough to ensure sensitivity for full range of light paths







Possible candidates:

-UV/visible: O2, O4 (oxygen dimer)

-Near IR: O2, CO2, CH4(what about water vapor?)







Possible candidates:

-UV/visible: O2, O4

-Near IR: O2, CO2, CH4(what about water vapor?)

used in this study

O4

O2

Atmospheric height profiles




O4-Absorptionen (Greenblatt et al., 1990)

300 350 400 450 500 550 600 650 700Wellenlänge [nm]

O4 absorption bands in the UV/vis spectral region

O2 absorption




O4-Absorptionen (Greenblatt et al., 1990)

300 350 400 450 500 550 600 650 700Wellenlänge [nm]

O4 absorption bands analysed in GOME spectra

O4 360 nm

-0.025

-0.02

-0.015

-0.01

-0.005

0

0.005

348 353 358 363 368 373

Wavelength [nm]

OD

-0.08-0.06-0.04-0.020.00

-0.20-0.15-0.10-0.050.00

O4

O2

610 620 630 640 650 660 670 680

Wavelength [nm]

O2 absorption




Ring effect:‚Filling-in‘ of Fraunhofer lines due to rotational Raman-scattering

Solar Fraunhofer line in directand scattered light

Ratio spectrum of scatteredand direct solar light

320 340 360 380 400Wavelength [nm]

Ref

lect

ivity







320 340 360 380 400Wavelength [nm]

Ref

lect

ivity

The Ring effect is strongest in the UV

5.0E-2

1.0E-1

1.5E-1 Ring

344 348 352 356 360Wavelength [nm]

-0.06

-0.04Ring

610 630 650 670

Wavelength [nm]

Optical depth

≈ 10%

Optical depth

≈ 2%

GOME red GOME UV







320 340 360 380 400Wavelength [nm]

Ref

lect

ivity

• The strength of the Ring effect depends on the relative fraction of photons which have undergone (inelastic) Raman-scattering

• elastic processes are: -Rayleigh-scattering

-aerosol-scattering

-ground reflection




Instrument

Green points indicate scattering points of photons => reception area of the detectorBackward Monte Carlo

(TRACY-II)

Tim Deutschmann, IUP Heidelberg

Realistic modelling of microscopic and macroscopic cloud properties

aerosol layer

Instrument

aerosol layer





Instrument

Green points indicate scattering points of photons => reception area of the detectorBackward Monte Carlo

(TRACY-II)


Realistic modelling of microscopic and macroscopic cloud properties

aerosol layer

Instrument

aerosol layer


Instrument

Strong forward peak

aerosol layer

Moderateforward peak

Suniti Sanghavi, IUP Heidelberg




Model results as function of cloud altitude:(Preliminary results)

Different dependence for O2 and O4

• Absorption is expresses as air mass factor (AMF)

• It is a measure of sensitivity

• AMF = 1 indicates an absorption corresponding tothe vertical atmospheric column






Ring effect shows monotonous decrease






Ring effect shows monotonous decrease

Intensity and photon pathincrease slightly

+ information onscattering statistics





Absorptions become higher than for clear skies

Intensity and photon pathmuch higher than for lowOD




-60 -30 0 30 60Latitude

0.2

0.4

0.6

[rel.

units

]

20

40

60

SZA

[]

Ring 370nm

O2 630nm

O4 630nm

SZA

O4 370nm

GOME orbit, 81120145

0.0

0.5

1.0

Clo

ud F

ract

ion

0

2

4

6

[rel.

units

]

0123

O4

AMF

0123

O4

AMF

GOME measurements

Typically the shielding effect ofclouds is dominant

It can be caused by clouds or mountains




-60 -30 0 30 60Latitude

0.2

0.4

0.6

[rel.

units

]

20

40

60

SZA

[]

Ring 370nm

O2 630nm

O4 630nm

SZA

O4 370nm

GOME orbit, 81120145

0.0

0.5

1.0

Clo

ud F

ract

ion

0

2

4

6

[rel.

units

]

0123

O4

AMF

0123

O4

AMF

GOME measurements

Sometimes, strongly enhanced absorptions indicate long light paths inside clouds

The Ring effect shows noenhancement




The high values occur at the edge of an extended cloud




The cloud is also seen by the microwave measurements (liquid water path)




-60 -30 0 30 60Latitude

0.2

0.4

0.6

rel.

units

20

40

60

SZA

Ring 370nm

O2 630nm

O4 630nm

SZA

O4 370nm

GOME orbit, 81114194 (narrow mode)

0.0

0.5

1.0

Clo

ud ra

ctio

n

0123

O4

AMF

0123

O4

AMF

0

2

4

6

rel.

units

GOME measurements

Additional examples of strongly enhanced absorptions

(about 10 per month)




Conclusions

• Spectral measurements (O2 & O4 absorption & Ring effect) offer new kindof information on clouds:

• Average light paths inside (or between) clouds

• Spatial information (also horizontal, 3D???)

• scattering statistics (number of Mie-scattering events, etc...)

• Monte-Carlo radiative transfer modelling provides optimum link between observations and macroscopic and microscopic cloud properties

• Strongly enhanced absorptions found in GOME data (about 10 times permonth, especially frequent for narrow swath mode)




Outlook

• Additional light path tracers:

-CO2, CH4, O2 in near IR, Intensity, Colour index

• More accurate RTM:

-O4 temperature dependence

-strong & narrow absorbers

• Comprehensive analysis of observations

-global statistics of light paths, scattering statistics, etc..

• Helpful: smaller size of ground pixels for SCIA & GOME-2

traditional‘ satellite methods (clouds are bright) • what...

Documents