Visual range measurement

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... 

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. 

Ozkaynak, H., A. D. Schatz, G. D. Thurston, R. G. Isaacs, and R. B. Husar, Relationships between Aerosol Extinction Coefficients Derived from Airport Visual Range Observations and Alternative Measures of Airborne Particle Mass, J. Air Pollut. Control Assoc., 35, 1176-1185 (1985). 

First rough estimation of linear range measure blank + minimum of six independent concentration levels, set up calibration curve and estimate linear range visually... 

Long term observations indicate that UV-B radiation reaching the earth s surface may have decreased by 5-18% since the industrial revolution in the industrialised midlatitudes of the Northern Hemisphere (NH). However, on a global basis, this may have been offset by the stratospheric ozone layer reduction. It is not possible to estimate the net effect from both, attenuation and increase, because of the limited amount of spatial and temporal coverage of measurements (Liu et al., 1991). In an attempt to present calculated and modelled effects of aerosol on UV flux the authors used the Discrete Ordinate Radiative Transfer Model (DISORT Stammes et al. 1988) for different visual ranges and boundary layer depths (Figure 1). The decrease at 310 nm is 18% and 12 % for a 2km and 1km PBL respectively. 

Transmissometers in simplest form consist of a light source and a detector located some distance along the axis of the light beam. Among their applications, these devices are commonly used at airports to provide data in visual ranging conditions and are used to measure particle loadings in smokestacks. When calibrated for the type of particles present in this aerosol, a semiquantitative measure of the particulate emissions can be made, with knowledge of the volumetric gas flow. 

One of the most widely recognized aspects of atmospheric pollution is reduced visibility, which is due primarily to light extinction by particles. A common measure of visibility is visual range (F/ ), which is defined as the maximum distance at which a black object can be seen against the horizon, as follows ... 

Optical densities were measured in 4 cm cells with a Unicam SP600 visual range... 

When the data set is being examined visually, several measurements can already be marked as potentially bad data, especially the measurements that lie considerably out of the expected range of the process. But there are also bad data that are not directly visible. Therefore several methods have been developed to recognize this. One of these methods, the principal component analysis, will be discnssed in the following chapter, but its merits will already be shown here. 

Above Re = 10 the vortex shedding is difficult to see in flow visualization experiments, but velocity measurements still show a strong spectral component at St = 0.2 (Panton, p. 392). Experimental data suggest that the vortex street disappears over the range 5 X 10 < Re < 3.5 X 10 , but is reestablished at above 3.5 X 10 (Schhchting). 

If results of color measurements are expressed in Munsell notation, a reader can use Munsell color charts as an aid in visualizing approximate ranges of color differences involved. Such a means has been suggested (15) for expressing color of light-colored juices. The necessary experimental data were obtained with a reflection meter similar to the reflectometer described. 

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