Field Spectroscopy Hyperspectral Imaging Applications in Vegetation and

Field Spectroscopy, Hyperspectral Imaging, Applications in Vegetation and Soils Analysis Alexander F. H. Goetz University of Colorado and Analytical Spectral Devices Inc. goetz@cses. colorado. edu Beijing and Nan. Jing, China June 28 -29 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 http: //speclab. cr. usgs. gov • Dr. Greg Swayze, USGS gswayze@usgs. gov • Dr. Joe Boardman, AIG LLC www. aigllc. com • Dr. Fred Kruse, Horizon Geo. Imaging LLC www. hgimaging. com • Dr. Brian Curtiss, Analytical Spectral Devices Inc. www. asdi. com • Ms. Phoebe Hauff, Spectral International Inc, www. specmin. com

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 400 -2500 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

Terra. Spec Field. Spec Pro

High Intensity Probe Attaches to Field. Spec or Terra. Spec

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 (Ca. F 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 2. 6 -6 m region, overtones and combinations found in VNIR, SWIR • 3 N-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 , 2 1 + 3, 1 + 2 + 3, …. • Frequencies not wavelengths added • • Frequency units in cm-1 • 2. 5 m = 4000 cm-1

WATER VAPOR • Absorption fundamentals • 1 = 3657. 05 cm-1 = 2. 734 m symmetric stretch • 2 = 1594. 75 cm-1 = 6. 271 m bend • 3 = 3755. 93 cm-1 = 2. 662 m asymmetric stretch • Important water vapor absorptions • 2 + 3 = 1. 865 m • 1 + 3 = 1. 379 m • 1 + 2 + 3 = 1. 135 m • 2 1 + 3 = 0. 942 m

LIQUID WATER • Absorption fundamentals • 1 = 3219. 57 = 3. 106 m • 2 = 1644. 74 = 6. 08 m • 3 = 3444. 71 = 2. 903 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 FEATURE POSITION Fe 3+ 0. 4 - 0. 6 m, 0. 66 m, 0. 85 0. 95 m Al - OH 2. 15 - 2. 22 m Mg - OH 2. 30 - 2. 39 m Fe - OH 2. 24 - 2. 27 m Si - OH 2. 25 m (broad) H 2 O 1. 9 m CO 3 2. 30 - 2. 35 m NH 4 2. 0 - 2. 13 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 183 -501 4800 Oak Grove Drive Pasadena, CA 91109 Phone: 818 -354 -0974 Fax: 818 -354 -0966 E-mail: Simon. J. Hook@jpl. nasa. gov Web: http: //speclib. jpl. nasa. gov/

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: +61 -2 -94908839 E-mail: Jon. Huntington@csiro. au Web: http: //www. syd. dem. csiro. au/research/MMTG/

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 80225 -0046 Phone: 303 -236 -1332 Fax: 303 -236 -1425 E-mail: rclark@usgs. gov Web: http: //speclab. cr. usgs. gov/