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

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

3. Spectra vary
with composition
Minerals
Ices

4. 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

5. 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

6. 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

7. 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

9. Particle size affects spectra
H2O
Pyroxene

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

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

12. 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

13. 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

14. 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

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

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

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

18. 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

19. Next Class:
Satellites
Review for Midterm