Radiometry – Remote sensing via microwave emission辐射–通过微波辐射遥感.ppt

Radiometry – remote sensing via microwave emission Outline Thermal radiation Blackbody radiation and Planck’s law Stefan-Boltzmann law Emissivity, graybodies, selective radiators Rayleigh-Jeans approximation Temperature Brightness temperature Apparent temperature Antenna temperature Radiative transfer Extinction (absorption and scattering) Emission Apparent temperature of terrain Thermal radiation Emission (or absorption) of radiated energy may be the result of an atom-bound electron transitioning from one energy level to another or from a change in a molecule’s vibrational or rotational mode. In atomic and molecular gases these energy transitions are represented by a set of energy levels forming discrete lines in the electromagnetic spectrum. In liquids and solids the interaction between particles increases the number of degrees of freedom complicating the radiated (and absorbed) spectral characteristics. The probability of interactions is related to the atom’s or molecule’s kinetic energy in its random motion. Since a substance’s kinetic (or heat) energy is represented by its absolute temperature, the radiated energy intensity increases with temperature. Blackbody radiation and Planck’s law Using classical physics (mechanics), theories were put forth by Wilhelm Wien (1893) and Lord Rayleigh (1900) that, in a piecemeal fashion, agreed well with experimentally measured radiative emissions. While the Wein law was valid for shorter (optical) wavelengths, the Rayleigh law was valid for longer wavelengths. In 1905 Lord Rayleigh and Sir James Jeans offered a more complete theory was presented (Rayleigh-Jeans law) that again only agreed well with experimental measurements at long wavelengths. Max Planck’s blackbody radiation law (1901) accurately predicted the spectral intensity of electromagnetic radiation at all frequencies or wavelengths by incorporating quantum theory. Blackbody radiation and Planck’s law Notation for radiometric quantities Planck’s blackbody radiati