The range of validity of the anomalous diffraction approximation to electromagnetic scattering by a sphere.
The ranges of refractive index and particle size over which the anomalous diffraction approximation is valid to within 15%, 50%O, and 100% are mapped. The approximation is found to have a broader range of applicability for the extinction efficiency than the Rayleigh-Gans approximation. The large range of validity explains the success of schemes for determining particle size distributions of spheres from extinction measurements based on analytic inversions of formulas containing the approximation.
Aerosol studies by light scattering. V. Preparation and particle-size distribution of aerosols consisting of particles exhibiting high optical absorption
Aerosols consisting of solid spheres have been prepared in a newly designed generator by two-stage evaporation-condensation of vanadium pentoxide in a furnace capable of operating up to 1500”. Nuclei were prepared by evaporation of aluminum a t 1000”, condensation to an aluminum aerosol, and subsequent burning in oxygen to A1203. The particle size distribution of the aerosols was determined by analysis of the angular distribution of the polarization of the scattered light. The special feature of this work resides in the high optical absorption of aerosol particles a t the blue end of the visible spectrum (comparable to that of metals) and the low absorption a t the red end (comparable to dielectrics). By considering several wavelengths, the very different scattering data on the same physical system led to size distributions which agreed with each other. The uniqueness of these results was explored with the aid of error contour maps.
Thermal remote sensing
Thermal Atmospheric Windows • The signal in the thermal infrared portion of the spectrum is caused by emission of electromagnetic radiation emitted from the earth. Thermal infrared region runs from 3-14 μm; • Large portions of this spectral region are affected by atmospheric absorption (blinds); • Typically remote sensing utilizes the 3-5μm wavelengths and 8-14μm wavelengths; • Ozone strongly absorbs in 9.2-10.2μm range, so this range is cannot be utilized by spacecraft remote sensing systems, but can be used by airborne systems. • Dominant wavelength of the emitted energy from Earth’s surface 9.7 μm. • 3-5μm region is especially useful for monitoring hot targets such as forest fires and geothermal activities. • Vegetation, soil rock are best monitored using the 8-14μm region for suborbit data collection. 10.5-12.5μm region is used when thermal imagery is acquired from orbital sensors above the Earth’s ozone layer. Fundamentals of Thermal Remote Sensing Wien's Displacement Law • Wavelength at which the largest portion of energy is emitted from a blackbody depends on temperature.