Lecture 9: Spectroscopy Wednesday, 2 February 2011 Lecture 9: Spectroscopy Reading Ch 5.14 Ch 6.1-3 Ch 4.5

What was covered in the previous lecture 1) reflection/refraction of light from surfaces (surface interactions) Last Friday’s lecture: 2) volume interactions - resonance - electronic interactions - vibrational interactions Today’s lecture 3) spectroscopy - continuum vs. resonance bands - spectral “mining” - continuum analysis and 4) spectra of common Earth-surface materials LECTURES Jan 05 1. Intro Jan 07 2. Images Jan 12 3. Photointerpretation Jan 14 4. Color theory Jan 19 5. Radiative transfer Jan 21 6. Atmospheric scattering Jan 26 7. Lambert’s Law previous Jan 28 8. Volume interactions today Feb 02 9. Spectroscopy Feb 04 10. Satellites & Review Feb 09 11. Midterm Feb 11 12. Image processing Feb 16 13. Spectral mixture analysis Feb 18 14. Classification Feb 23 15. Radar & Lidar Feb 25 16. Thermal infrared Mar 02 17. Mars spectroscopy (Matt Smith) Mar 04 18. Forest remote sensing (Van Kane) Mar 09 19. Thermal modeling (Iryna Danilina) Mar 11 20. Review Mar 16 21. Final Exam 2

Discussion: 1) reflection/refraction of light from surfaces (surface interactions) 2) volume interactions - resonance - electronic interactions - vibrational interactions 3) spectroscopy - continuum vs. resonance bands - spectral “mining” - continuum analysis 4) spectra of common Earth-surface materials

Spectra vary with composition Minerals Ices CaCO3 MgCO3 Be3Al2(SiO3)6 CaSO42(H2O) KAl(SO4)212H2O KFe+33(OH)6(SO4)2

Fig 2.21, Siegal & Gillespie For silica in TIR Thermal infrared Molecular vibration modes in silicates affect the thermal infrared Fig 2.21, Siegal & Gillespie For silica in TIR Thermal infrared silicates

Reflectance spectrum of SiO2 in the TIR QUARTZ: SiO2 The doubled peak is due to crystallographic asymmetry (hexagonal) in quartz The silica tetrahedron is distorted in quartz: the Si-O bond down the c-axis has a different length than it does across it

Phase affects spectra Ice – liquid transition for water Bands don’t broaden much as ice turns to water Band centers shift subtly Amount of absorption increases with optical length z in Beer’s law (e-kz) – there are no grain interfaces in water. This is a particle size affect Low water content Ice – liquid transition for water High water content

Particle size affects spectra Coarse particles – spectra dominated by absorption inside grains Fine particles – spectra dominated by surface reflection Low surface/volume ratio Average optical path is long High surface/volume ratio Path is shorter

Particle size affects spectra H2O Pyroxene XY(Si,Al)2O6

Spectral resolution: multispectral remote sensing vs. imaging spectroscopy KAl(SO4)212H2O Imaging spectroscopy is more likely to resolve absorption bands

Spatial resolution also affects spectra (by mixing) KAl(SO4)212H2O KFe+33(OH)6(SO4)2 Areal (checkerboard) mixing: additive Intimate mixing: “subtractive”

Intimate mixing can be highly non-linear Adding highly absorptive charcoal greatly reduces the optical path length (“z” in Beer’s Law: e-kz) A small amount has a large effect Larger amounts have diminishing effect

Spectroscopy considerations - continuum vs. resonance bands Absorption bands are measured relative to the “continuum” – the value of the spectrum if the absorption band was not present

Discussion: 1) reflection/refraction of light from surfaces (surface interactions) 2) volume interactions - resonance - electronic interactions - vibrational interactions 3) spectroscopy - continuum vs. resonance bands - spectral “mining” - continuum analysis 4) spectra of common Earth-surface materials

Spectra of common Earth-surface materials SOIL Path length Clay H2O Fe-O Water absorption

Spectra of common Earth-surface materials Cellular scattering Green Vegetation Water absorption Chlorophyll absorption

Spectra of common Earth-surface materials Dry Vegetation Cellulose Cellular scattering Water absorption Chlorophyll absorption

Leaf structure and its relation to spectra Absorption band in red: chlorophyll pigment Reflective NIR: scattering in the prismatic leaf cells SWIR absorption: absorption by leaf water

Next Class: Satellites & orbits Review for Midterm