Visual range

Visibihty or visual range is the maximum distance at which a black object, a target, can be distinguished from the horizon. Under certain viewing conditions, the apparent contrast (C) between a target and the horizon decreases exponentially with the distance (x) between the target and observer (42)... 

Standard polyester fibers contain no reactive dye sites. PET fibers are typically dyed by diffusiag dispersed dyestuffs iato the amorphous regions ia the fibers. Copolyesters from a variety of copolymeri2able glycol or diacid comonomers open the fiber stmcture to achieve deep dyeabiHty (7,28—30). This approach is useful when the attendant effects on the copolyester thermal or physical properties are not of concern (31,32). The addition of anionic sites to polyester usiag sodium dimethyl 5-sulfoisophthalate [3965-55-7] has been practiced to make fibers receptive to cationic dyes (33). Yams and fabrics made from mixtures of disperse and cationicaHy dyeable PET show a visual range from subde heather tones to striking contrasts (see Dyes, application and evaluation). 

Tombach, 1., "A Critical Review of Methods for Determining Visual Range in Pristine and Near-Pristine Areas," Proceedings of the Annual Meeting of the Air Pollution Control Association, Pittsburgh, 1978. 

A simplified relationship developed by Koschmieder which relates the visual range and the extinction coefficient is given by Eq. (10-3),... 

While the Koschmieder relationship is useful as a first approximation for determining visual range, many situations exist in which the results are only qualitative. 

The Rayleigh scattering extinction coefficient for particle-free air is 0.012 km for "green" light (y = 0.05 /rm) at sea level (4). This permits a visual range of —320 km. The particle-free, or Rayleigh scattering, case represents the best visibility possible with the current atmosphere on earth. 

Atmospheric haze has been observed in both the western and eastern portions of the United States. Typical visual ranges in the East are <15 miles and in the Southwest >50 miles. The desire to protect visual air quality in the United States is focused on the national parks in the West. The ability to see vistas over 50-100 km in these locations makes them particularly vulnerable to atmospheric haze. This phenomenon is generally associated with diffuse or widespread atmospheric degradation as opposed to individual plumes. 

Zannetti et al. (20) did an analysis of visual range in the eastern United States again showing the importance of humidity but also showing the importance of air mass type, which is usually related to its direction of origin. 

Zannetti, P., Tombach, I. H., and Cvencek, S. ]., An analysis of visual range in the eastern United States under different meteorological regimes. /, Air Pollut. Control 39,... 

Perceived visual quality, atmospheric color, plume blight, visual range... 

Flexibility, judgment large existing data base (airport visual range)... 

Labor intensive variability in observer perception suitable targets for visual range not generally available... 

Complement to instrumental observations areas with frequent plume blight, discoloration visual ranges with available target distances Areas experiencing periodic, well-mixed general haze medium to short viewing distances small absorption coefficient (b ) relating to point comptosition measurements... 

Haze (Hazy) an atmospheric aerosol of sufficient concentration to be visible. The particles are so small that they cannot be seen individually, but are still effective attenuating light and reducing visual range. 

Natural Conditions conditions substantially unaltered by humans or human activities, as applied in the context of visibility, natural conditions include naturally occurring phenomena that reduce visibility as measured in terms of light extinction, visual range, contrast, or coloration. 

Regional Haze Visibility Impairment any humanly perceptible change in visibility (light extinction, visual range, contrast, coloration) from that which would have existed under natural conditions, caused predominantly by a combination of many sources from, and occurring over, a wide geographic area. 

Visual Range the distance at which a large black object would just disappear from view. 

Seh-rohr, n. periscope telescope viewing tube. -schMrfe, /. sharpness of vision, -weitc, /. visual range or distance, -zelle, /-visiial cell. 

Fluorescence spectroscopy is commonly used to characterize fluorescence effects in the UV and visual range of the electromagnetic spectrum. Such fluorescence is caused by the fact that the absorption of UV or visible light of specific wavelengths causes excitation of electrons within a molecule. If radiating relaxation occurs directly from the singlet Sj state, the process is called fluorescence. 

A proper control strategy for visibility protection at a given location requires information about the relationship between each source and its contribution to a quantity called the extinction coefficient, bg. The visual range, Vj, and bg are related through the Koschmieder equation (1 ). 

When only the fine aerosol (D <2 ym) is considered, it is seen that the calculated scattering coefficient, bgpi> agrees very well with the data. In a statistical analysis, bgo was very well correlated with the volume of fine particles, r = 0.81, but not with the total volume of particles smaller than 10 ym, r = 0.44. Similarly, Trijonis and Yuan 3) found that the total concentration was a poor indicator of visual range in Phoenix. 

Aerosol Species Average Mass Extinction Efficiency mVg % Decrease in Current Visual Range Due to Additional 2 pg/m of Species... 

---