Paul Geladi feb 06
Is Hyperspectral Imaging an Analytical Instrument?
Paul Geladi feb 06
Paul Geladi
Head of Research NIRCEChairperson NIR Nord
Unit of Biomass Technology and ChemistrySwedish University of Agricultural SciencesUmeåTechnobothniaVasa
paul.geladi @ btk.slu.se paul.geladi @ uwasa.fi
Paul Geladi feb 06
Paul Geladi feb 06
Content
• Short introduction of the topic
• Space imaging
• Instrumentation
• Examples, history and philososphical thoughts
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Multivariate Image
K << I ≈ J
I
J
K
I
J
K
HyperspectralImageK≈I≈J
What is a hyperspectral image?
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256
320
128
512
614
224
MatrixNIR
AVIRIS
First defined in airborne imaging
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Na Mg
Al Si
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Cr Fe
Ni
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Cu Zn
Van Espen P., Janssens G., Vanhoolst W. & Geladi P., Imaging and image processing in analytical chemistry, Analusis, 20, 81-90, 1992.
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Airborne hyperspectral imaging•http://www.microimages.com/getstart/hyprspec.htm
• Randall Smith 2001
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Some airborne systems
Sensor Country Nr bands Range m
AVIRIS USA 224 0.4 - 2.5
AISA FI 286 0.45 - 0.9
CASI CA 288 0.43 - 0.87
DAIS USA 211 0.4 - 12
HYMAP AU 128 0.4 - 2.45
PROBE1 USA 128 0.4 - 2.45
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Orig
Veg
Water
Soil
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Conclusions Airborne
• Not too much chemometrics
• Calibration / standardization / correction problems
• Comparison of airborne / ground spectra
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0 nm 3000 nm
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Lab versus airplane
• We have our own “sun”
• It is controllable
• Only within limits
• Problems still exist
• How to quantify / correct problems?
Paul Geladi feb 06
Content
• Short introduction of the topic
• Space imaging
• Instrumentation
• Examples, history and philososphical thoughts
Paul Geladi feb 06
AVIRIS
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Rotating filter wheel
Camera
Filter wheel
Field of study under polychromatic illumination
Signal out
Alternative: illumination diode array
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PbS camera
Fiber ring
Radiation source
Interference filters
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680 nm 740 nm 800 nm 840 nm
1010 nm 1110 nm 1200 nm
Geladi P, Sethson B, Nyström J, Lillhonga T, Lestander T & Burger J, Chemometrics in spectroscopy: Part 2. Examples, Spectrochimica Acta Part B: Atomic Spectroscopy, 59, 1347-1357, 2004.
Paul Geladi feb 06Prism-Grating -Prism
Prism
Grating
Prism
Focusing
Focusing
Rectangulardetector
Pushbroom
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Interferometer
Fixed mirror
Moving mirror
Semitransparentmirror (50%)
Detector(interferogram)
a
b
Sample (scan by moving)
Radiationsource
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Most FT-IRFT-Raman
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InGaAs array
LCTF
Objective
Sample(s)
Lamp(s)
≈5 cm
≈5 cm
To file
12 bit A/D convertor
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InGaAs array
LCTF
Objective
Sample(s)
Lamp(s)
≈5 cm
≈5 cm
To file
12 bit A/D convertor
256x3200.2x0.2 mm2 pixel
max 128 900-1700 nm
Paul Geladi feb 06
Paul Geladi feb 06
Content• Short introduction of the topic
• Examples, history and philososphical thoughts
• Standardization
• Calibration
• Sampling problems
• Comparison
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Paul Geladi feb 06
Edmundcatalog
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900 1000 1100 1200 1300 1400 1500 1600 17000
500
1000
1500
2000
2500
3000
3500
4000
4500
wavelength nm
A/D counts
Specular reflection
99%
2%
75%
50%
Raw A/D convertor data
Paul Geladi feb 06900 1000 1100 1200 1300 1400 1500 1600 1700
50
50.5
51
51.5
52
52.5
53
53.5
54
54.5
55
wavelength nm
Reflectance %
NIST calibration
Interpolation
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2%
25%
50%
75%
99%
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R= 1, 0.8, 0.6, 0.4
R= 0.2, 0.1, 0.05, 0
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Content• Short introduction of the topic
• Examples, history and philososphical thoughts
• Standardization
• Calibration
• Sampling problems
• Comparison
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Metal frame
2% refl.
50% refl. 75% refl.
99% refl.
Cheddar
Blue
Edam
Emmenthal
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Reference values (y)
• Pure standards
• Known mixtures
• Wet chemistry
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Reference values
• Impossible to measure wet chemistry in every pixel
• All standards are heterogeneous at high magnification
• Not always possible with synthetic standards
Geladi P., Burger J. & Lestander T., Hyperspectral imaging: calibration problems and solutions, Chemometrics and Intelligent Laboratory Systems, 72, 209-217, 2004.
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Content• Short introduction of the topic
• Space imaging
• Instrumentation
• Examples, history and philososphical thoughts
• Standardization
• Calibration
• Sampling problems
• Comparison
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One pixel
50/50 mixture
Sampling problem
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One pixel
50/50 mixture
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Paul Geladi feb 06
Content• Short introduction of the topic
• Examples, history and philososphical thoughts
• Standardization
• Calibration
• Sampling problems
• Comparison
• Examples (removed, paper in review)
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Comparison with a spectrometer
• Integration over a volume / area
• Only 1 detector• High resolution 216
• Wide range possible• Lower noise
• Information in pixels / depth?
• Many detectors• Low resolution 212
• Limited range• Noisier
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Comparison
• Linearity better controlled
• No populations• Quick
• Linear?• Missing pixels• Populations!• Slow
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Conclusions
• Airborne/space are ahead
• Many principles
• Instrument standardization needed
• No material is homogeneous at the nanolevel
• Camera ≠ spectrometer, but we get close
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Acknowledgements
Torbjörn Lestander, SLU, Umeå
Jim Burger, SLU, Umeå
EASIM European Association for Spectral Imaging
started in Umeå 14 February 2006
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