Field Spectroscopy, Hyperspectral Imaging, Applications in Vegetation and Soils Analysis Alexander F. H. Goetz University of Colorado and Analytical Spectral Devices Inc. Beijing and NanJing, China June and July 1-2, 2004 Lecture 1

Spectroscopy, Hyperspectral and Applications Day 1 Spectroscopy fundamentals Spectral Imaging Hyperspectral Data Analysis Day 2 Hyperspectral Data Analysis cont. Tradeoffs: Spatial, Spectral Resolution, SNR Applications

Acknowledgements Dr. Roger Clark, US Geological Survey Dr. Greg Swayze, USGS Dr. Joe Boardman, AIG LLC Dr. Fred Kruse, Horizon GeoImaging LLC Dr. Brian Curtiss, Analytical Spectral Devices Inc. Ms. Phoebe Hauff, Spectral International Inc,

Spectroscopy Fundamentals

Reflectance Instruments measure radiance L

Reflectance (2) In practice, the spectrometer is used to measure a white standard such as Spectralon®, which is sintered PFTE (polytetrafluoroethene)(Teflon®) It has a reflectance close to 100% over the nm region In the instrument, the radiance measured from the sample is ratioed with the Spectralon radiance to produce reflectance as a function of wavelength

ASD Spectrometers and Spectroradiometers

FieldSpec Pro TerraSpec

High Intensity Probe Attaches to FieldSpec or TerraSpec

Argentina 7000 m

Peanut Field, Argentina

PROCESSES THAT CAUSE ABSORPTION FEATURES Electronic Interactions between electrons and crystal fields Vibrational Molecular vibrations Fundamental Overtone Combination

ELECTRONIC PROCESSES Crystal field effects Charge transfer Semiconductor Color centers

CRYSTAL FIELD EFFECTS Energy levels of an ion Split and displaced in crystal field Determined by Valence state Coordination number and symmetry Reflectance spectrum Determined primarily by mineralogy not cation Depth of feature grain-size dependent

CRYSTAL FIELD EFFECTS Iron most important Most abundant Fe 2+, Fe 3+ can substitute Mg 2+ Al 3+

Ruby, Al 2 O 3 + Cr +++

Emerald, Be 3 Al 2 Si 6 O 18 + Cr +++

Electronic Transitions in Iron Minerals

Iron Minerals Lepidocrocite Ferrihydrite Maghemite Goethite Hematite

CHARGE TRANSFER Electrons transfer from one atom to another Fe-O transfer responsible for reflectance falloff towards UV

SEMICONDUCTORS Absorption edge in reflectance spectrum Created by width of forbidden energy band gap Incoming photons must have enough energy to promote valence band electrons into conduction band Reflectance increases dramatically at wavelength corresponding to band gap energy

COLOR CENTERS Electron trapped in a structural defect such as a missing ion In fluorite (CaF 2 ) a color center is formed when an F ion is missing and replaced by an electron Transition states created cause red-green absorption, hence purple color

VIBRATIONAL PROCESSES Fundamental vibrations For solids, generally occur beyond 2.5  m Si-O, Al-O occur in 10  m region, no effect in VNIR or SWIR OH, H 2 O, CO 3 occur in  m region, overtones and combinations found in VNIR, SWIR 3N-6 possible degrees of freedom H 2 O has 3 fundamental vibrations at 2.66, 2.74, 6.08  m

OVERTONES AND COMBINATIONS Overtones Multiples of the fundamental frequency 2 1, 3 2, ….. Combinations Sums and differences of fundamental or overtone frequencies 1 + 2, , , …. Frequencies not wavelengths added Frequency units in cm  m = 4000 cm -1

WATER VAPOR Absorption fundamentals 1 = cm -1 =  msymmetric stretch 2 = cm -1 =  mbend 3 = cm -1 =  masymmetric stretch Important water vapor absorptions =  m =  m =  m =  m

LIQUID WATER Absorption fundamentals 1 = =  m 2 = = 6.08  m 3 = =  m

HYDROXYL Absorption fundamental 2.77  m stretch Exact location depends on site on which it is located Overtone 2 ~ 1.4  m Most common feature in terrestrial material spectra Combinations Al or Mg - OH bending modes Features in 2.2 & 2.3  m region

SPECTRAL PROPERTIES SOME COMMON ABSORPTION FEATURES FEATUREPOSITION Fe  m, 0.66  m,  m Al - OH  m Mg - OH  m Fe - OH  m Si - OH2.25  m (broad) H 2 O1.9  m CO  m NH  m

Laboratory Spectra

Coatings (thin films) Absorption features are square root 2 (0.707) narrower width than thick particulate surfaces. Coatings vary from transmissive thin films to full scattering thick layers; the natural width of spectral features varies by root 2.

The variety of absorption processes and their wavelength dependence allows us to derive information about the chemistry of a mineral from its reflected or emitted light.

SELECTED DIGITAL SPECTRAL DATA BASES JPL Laboratory reflectance spectra of 2000 natural and man-made materials, 0.4 to 14 micrometers Contact: Dr. Simon Hook JPL, MS Oak Grove Drive Pasadena, CA Phone: Fax: Web:

SELECTED DIGITAL SPECTRAL DATA BASES CSIRO Spectral Library Contact: Dr. Jon Huntington CSIRO Division of Exploration & Mining P.O. Box 136 North Ryde, N.S.W., 1670 Australia Phone: Web:

SELECTED DIGITAL SPECTRAL DATA BASES USGS (Denver) Spectral Library Contact: Dr. Roger Clark U.S.G.S. P.O. Box 25046, MS 964 Denver, CO Phone: Fax: Web: