Lecture 9: Spectroscopy Tuesday, 3 February Lecture 9: Spectroscopy Reading assignment: Ch 7, Digital Image Processing -- 7.1 – 7.76 (p. 482 – 545)

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

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

Spectral resolution: multispectral remote sensing vs. imaging spectroscopy Imaging spectroscopy is more likely to resolve absorption bands

Spatial resolution also affects spectra (by mixing) Areal (checkerboard) mixing: additive Intimate mixing: “subtractive”

Intimate mixing can be highly non-linear Adding highly absorptive charcoal greatly reduces the optical path length (“d” in Beer’s Law: e-kd) 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” that is supposed to be the spectrum in the 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 Water absorption SOIL Path length Clay H2O Fe-O

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 Review for Midterm