Extinction, Scattering, and Absorption

Measurement over medium view path (10-25 km) measures total extinction, scattering and absorption unaffected by clouds, night... 

EXTINCTION, SCATTERING, AND ABSORPTION 3.4 EXTINCTION, SCATTERING, AND ABSORPTION... 

We may define efficiencies (or efficiency factors) for extinction, scattering, and absorption ... 

Several authors have addressed the determination of the optical properties of aqueous titanium dioxide suspensions in the context of photoreactor modeling (Brandi et al., 1999 Cabrera et al., 1996 Cured et al., 2002 Salaices et al., 2001, 2002 Satuf et al., 2005 Yokota et al., 1999). Among the determined properties are extinction, scattering, and absorption coefficients, as well as the asymmetry parameter of the scattering phase function. In general the procedures involve fitting of a radiative transfer model to the experimental results for reflectance and transmittance of radiation. 

FIGURE 24.10 Total extinction, scattering, and absorption coefficients for internal versus external mixtures of soot and (NH4)2S04. 

Essentially, Cgcat and Cabs represent the electromagnetic powers removed from the incident wave as a result of scattering and absorption of the incident radiation, while Cext gives the total electromagnetic power removed from the incident wave by the combined effect of scattering and absorption. The optical cross-sections have the dimension of area and depend on the direction and polarization state of the incident wave as well on the size, optical properties and orientation of the particle. The efficiencies (or efficiency factors) for extinction, scattering and absorption are defined as... 

It is interesting to compare these results with calculations of the triangle anteima in ftee space. Plots of the extinction, scattering, and absorption cross sections for the 100-nm triangle antenna in free space along with the peak field intensity at the apex are shown in Fig. 32. The resonance occurs at 675 nm, significantly shifted from the resonance wavelength in the presence of the medium. The peak field intensity occurs at the apex of the antenna, and is clearly... 

Figure 32. Extinction, scattering, and absorption cross sections normalized by the area of the antenna for the 100-nm triangle antenna on a glass substrate as a function of wavelength. The peak E field intensity versus wavelength is also plotted.

The extinction coefficient is dependent on the presence of gases and molecules that scatter and absorb light in the atmosphere. The extinction coefficient may be considered as the sum of the air and pollutant scattering and absorption interactions, as shown in Eq. (10-4) ... 

Suspended particles are the most important factor in visibility reduction. In most instances, the visual quality of air is controlled by partide scattering and is characterized by the extinction coeffident The size of particles plays a crucial role in their interaction with light. Other factors are the refractive index and shape of the particles, although their effect is harder to measure and is less well understood. If we could establish these properties, we could calculate the amount of light scattering and absorption. Alternatively, the extinction coeffident associated with an aerosol can be measured directly. 

Measurement over long view path (up to 100 km) with suitable illumination and target, contrast transmittance, total extinction, and chromaticity over sight path can be determined includes scattering and absorption from all sources can detect plume blight automated... 

Extinction the attenuation of light due to scattering and absorption as it passes through a medium. 

The extinction coefficient can be expressed as the sum of terms which account for light scattering and absorption by gases and suspended particles ( ) ... 

Light extinction Loss of light from a pathway from scattering and absorption of light by particles and gas molecules. 

The attenuation of a light beam is given in terms of the extinction coefficient, sometimes called the attenuation coefficient or turbidity, and it is a key measure of the optical behavior of particulate systems. In terms of the separate contributions for particle scattering and absorption,... 

Aerosol particle optical thickness AOT, Dimensionless Tep = J Oep Total optical thickness (or commonly optical depth) T= — In r cos 0g, where T is transmittance of direct solar beam for solar zenith angle 0q optical thickness (or commonly optical depth) due to extinction by aerosol particles r p = t — Tg, where Tg is optical thickness arising from scattering and absorption by gases depends on wavelength... 

The net result of absorption and scattering is extinction, while the light that is not extinct is said to be transmitted. In terms of the extinction efficiency, Q, which is defined as the ratio of the radiant power scattered and absorbed by a particle to the radiant power geometrically incident on the particle (proportional to the cross-sectional area). Therefore the extinction efficiency per cross-sectional area of the particle is the sum of its scattering and absorption efficiency per cross-sectional area, and Q, respectively ... 

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