paul geladi feb 06 is hyperspectral imaging an analytical instrument?

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?

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Content

• Short introduction of the topic

• Space imaging

• Instrumentation

• Examples, history and philososphical thoughts

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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

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Paul Geladi feb 06

Content• Short introduction of the topic

• Examples, history and philososphical thoughts

• Standardization

• Calibration

• Sampling problems

• Comparison

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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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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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