Post on 17-Jun-2020
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
13 October 2004CEOS-IVOS workshop 3
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.
13 October 2004CEOS-IVOS workshop 4
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
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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.
13 October 2004CEOS-IVOS workshop 6
Speckle with (partially) coherent light
Speckle pattern in partially coherent light, from LASERSPECKLES, J.C. Dainty (1975).
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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
13 October 2004CEOS-IVOS workshop 8
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
13 October 2004CEOS-IVOS workshop 9
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.
13 October 2004CEOS-IVOS workshop 10
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
13 October 2004CEOS-IVOS workshop 11
SF dedicatedMeasurement set-up
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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
13 October 2004CEOS-IVOS workshop 13
Speckle Model (2)
13 October 2004CEOS-IVOS workshop 14
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 ??? bazalgette@tpd.tno.nl
13 October 2004CEOS-IVOS workshop 15
Jokers
13 October 2004CEOS-IVOS workshop 16
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 [
-]
13 October 2004CEOS-IVOS workshop 17
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