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