Grégory Bazalgette Courrèges-Lacoste Diffuser trade-off ... · Grégory Bazalgette Courrèges-Lacoste. CEOS-IVOS workshop 13 October 2004 2 Contents

13 October 2004CEOS-IVOS workshop

TNO TPD

Diffuser trade-off study vsspectral features

Grégory Bazalgette Courrèges-Lacoste

13 October 2004CEOS-IVOS workshop 2

Contents

Spectral features overview

Speckle theory vs spectral features

Diffuser trade-off study


On-board diffuser on earthobservation satellites Instruments for atmospheric space research measure the sunlight

diffusely reflected and absorbed in the atmosphere and at theEarth’s surface.

As a reference spectrum for atmospheric measurements the diffusereflection of the sun is measured via an ‘on-board diffuser’ in thesatellite sensor.

on-board diffusers add a spectral signature to the diffusely scatteredsunlight that may resemble certain spectral characteristics of theatmosphere, the so-called SPECTRAL FEATURES.


Spectral features on diffusers

Spectral features dedicated set-up

spectral features on Aluminium diffuser

GOME 2 FM2 spectralfeatures on Aluminiumdiffuser

98.0%

100.0%

102.0%

104.0%

106.0%

108.0%

110.0%

112.0%

114.0%

0 200 400 600 800 1000

Wavelength [nm]

Ra

tio


Theoretical approach : speckle effect

-5 -4 -3 -2 -1 0 1 2 3 4 5 -5

-4

-3

-2

-1

0

1

2

3

4

5

Position [m]

Position [m]

-5 -4 -3 -2 -1 0 1 2 3 4 5 -5

-4

-3

-2

-1

0

1

2

3

4

5

Position [m]

Position [m]

#22.1..

61.0 fAN

ds !!=!= ""

I

I

II

IIC

!=

+

"=

minmax

minmax

Speckle contrast

Speckle size

Speckle effect = interference of coherent (or partially coherent) beams ofradiation from many secondary light point sources located on the roughsurface of an object.


Speckle with (partially) coherent light

Speckle pattern in partially coherent light, from LASERSPECKLES, J.C. Dainty (1975).


Spectral features vs speckle effect

Spectral features on Aluminium diffuser

-6.0%

-4.0%

-2.0%

0.0%

2.0%

4.0%

6.0%

360 460 560 660 760

Wavelength [nm]

Rati

o

Entrance slit of thespectrometer

Diffuser surface Spectral features

Detector pixels

(Partially)coherent light ona rough surface

Dispersion

Variation of thenumber of speckleson a detector cell


Spectral features empirical formula

( )Q

P

aInd.Spectr#

ëf

speckles#

VCV

speckles

SF !!!=

Effect of thepolarization

Diffuserquality factor

Contrast in thespeckle patternScaling factor

Number of independent specklepatterns that are being

averaged during a recording

Wavelengtheffects


Diffuser trade-off

Objectives : establish appropriate diffuser technologyfor on-ground calibration/validation and for the on-board calibration systems to be used in future earthobservation mission.

Measurement programme :

Measurement and analysis of Spectral features of 5diffusers over the spectral range 250-1600 nm (2400).

Measurement of the effect of environment(air/vacuum/degradation) on diffuser’s BSDF accuracyover the spectral range 280 –1000 nm.


TNO TPDQVDMaterial = QuartzSpace qualified = Yes (GOME2, OMI, …)

NPLWhite TileMaterial = Depolished white ceramicSpace qualified = No

AvianTechnology

FLUORIONMaterial = PTFESpace qualified = No

LabsphereSPECTRALONMaterial = PTFESpace qualified = Yes (MERIS, …)

TNO TPDAluminiumMaterial = AluminiumSpace qualified = Yes (SCIAMACHY, …)

ProviderDiffuser type


SF dedicatedMeasurement set-up


Speckle Model (1)

The Test facility has been modeled using the 1D Spectral Features analysis package (in MatLab).

The modeling consists of four steps : A simulation of the scattering surface has to be made (the diffuser) The optical beam has to be propagated towards an intermediate image (free space propagation) Fourier Transform mode as performed by a single lens Integrate the intensity over the entrance slit

SPECTROMETER MODULE

ILLUMINATION MODULE

DIFFUSER MODULE

IMAGING MODULE


Speckle Model (2)


Conclusion Relationship between spectral features and speckle effect

Spectral features measurement program : 5 diffuser types (surface, volume, stacked) Measured over the spectral range 250 nm –1600 nm Results extrapolated up to 2400 nm thanks to the speckle model

Measurement campaign begins on Friday at TNO TPD

___________________________________________________________

Which instruments are affected ??? [email protected]


Jokers


Spectral features on diffusersSpectral features dedicated set-upspectral features on Aluminium diffuser

GOME 2 FM2 spectralfeatures on Aluminiumdiffuser

TNO TPD

Spectral Features Scan

0,970

0,980

0,990

1,000

1,010

1,020

1,030

1,040

850 900 950 1000

Wavelength [nm]

Sig

nal R

ati

o [

-]

TNO TPD

Spectral Features Scan

0,980

0,985

0,990

0,995

1,000

1,005

1,010

1,015

1,020

390 440 490 540

Wavelength [nm]

Sig

nal R

ati

o [

-]


Spectral features dependenciesSpectral features in the UV range

-0.10%

-0.08%

-0.06%

-0.04%

-0.02%

0.00%

0.02%

0.04%

0.06%

0.08%

0.10%

280 290 300 310 320 330 340 350 360

Wavelength [nm]

Rati

o

Spectral features in the visible range

-6.0%

-4.0%

-2.0%

0.0%

2.0%

4.0%

6.0%

360 460 560 660 760

Wavelength [nm]

Rati

o

Spectral features measured with a point source

-2.0%

-1.5%

-1.0%

-0.5%

0.0%

0.5%

1.0%

1.5%

2.0%

0 200 400 600 800 1000

Wavelength [nm]

Rati

o

Spectral features measured with an extended source

-2.0%

-1.5%

-1.0%

-0.5%

0.0%

0.5%

1.0%

1.5%

2.0%

0 200 400 600 800 1000

Wavelength [nm]

Rati

o

Spectral features on Aluminium diffuser

-6.0%

-4.0%

-2.0%

0.0%

2.0%

4.0%

6.0%

360 460 560 660 760

Wavelength [nm]

Rati

o

Spectral features on QVD (Quasi-Volume Diffuser)

-0.5%

-0.4%

-0.3%

-0.2%

-0.1%

0.0%

0.1%

0.2%

0.3%

0.4%

0.5%

360 460 560 660 760

Wavelength [nm]

Rati

o

Wavelength Light sourcecharacteristics

Diffuser material

Documents

Grégory Bazalgette Courrèges-Lacoste Diffuser trade-off ... · Grégory Bazalgette Courrèges-Lacoste. CEOS-IVOS workshop 13 October 2004 2 Contents