Book contents
- Frontmatter
- Contents
- Introduction to first edition
- Introduction to second edition
- 1 Foundation of radiation theory
- 2 Radiative transfer
- 3 Interaction of radiation with matter
- 4 The emerging radiation field
- 5 Instruments to measure the radiation field
- 6 Measured radiation from planetary objects up to Neptune
- 7 Trans-Neptunian objects and asteroids
- 8 Retrieval of physical parameters from measurements
- 9 Interpretation of results
- Closing remarks
- Appendices
- References
- Abbreviations
- Index
3 - Interaction of radiation with matter
Published online by Cambridge University Press: 07 September 2009
- Frontmatter
- Contents
- Introduction to first edition
- Introduction to second edition
- 1 Foundation of radiation theory
- 2 Radiative transfer
- 3 Interaction of radiation with matter
- 4 The emerging radiation field
- 5 Instruments to measure the radiation field
- 6 Measured radiation from planetary objects up to Neptune
- 7 Trans-Neptunian objects and asteroids
- 8 Retrieval of physical parameters from measurements
- 9 Interpretation of results
- Closing remarks
- Appendices
- References
- Abbreviations
- Index
Summary
The discussions of the equation of transfer and the solution of this equation in Chapter 2 rest entirely on concepts of classical physics. Such treatment was possible because we considered a large number of photons interacting with a volume element that, although it was assumed to be small, was still of sufficient size to contain a large number of individual molecules. But with the assumption of many photons acting on many molecules we have only postponed the need to introduce quantum theory. Single photons do interact with individual atoms and molecules. The optical depth, τ(υ), depends on the absorption coefficients of the matter present, which must fully reflect quantum mechanical concepts. The role of quantum physics in the derivation of the Planck function has already been discussed in Section 1.7. Both the optical depth and the Planck function appear in the radiative transfer equation (2.1.47).
The interaction of radiation with matter can take many forms. The photoelectric effect, the Compton effect, and pair generation–annihilation are processes that occur at wavelengths shorter than those encountered in the infrared. Infrared photons can excite rotational and vibrational modes of molecules, but they are insufficiently energetic to excite electronic transitions in atoms, which occur mostly in the visible and ultraviolet. Therefore, a discussion of the interaction of infrared radiation with matter in the gaseous phase needs to consider only rotational and vibrational transitions, while in the solid phase lattice vibrations in crystals must be included.
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- Exploration of the Solar System by Infrared Remote Sensing , pp. 58 - 128Publisher: Cambridge University PressPrint publication year: 2003