Radiation interception

In order to compute the thermal radiation effects produced by a burning vapor cloud, it is necessary to know the flame s temperature, size, and dynamics during its propagation through the cloud. Thermal radiation intercepted by an object in the vicinity is determined by the emissive power of the flame (determined by the flame temperature), the flame s emissivity, the view factor, and an atmospheric-attenuation factor. The fundamentals of heat-radiation modeling are described in Section 3.5. 

Radiation effects from a flash fire are now fully determined if vapor cloud composition, as well as the geometry of the flame front (dependent on time), is known. Vapor cloud composition is, of course, place- and time-dependent, and the shape of flame front will greatly depend on cloud shape and ignition site within the cloud. The total radiation intercepted by an object equals the surmnation of contributions by all successive flame positions during flame propagation. This is an impossible value to compute with the simplified approach just described. Because there are many uncertainties (e.g., cloud composition, location of ignition site) which greatly influence the final result, a conservative approach is recommended for practical applications ... 

The factor n is required by the experimental conditions, under which the amount of incident radiation intercepted by the face of the crystal increases linearly with the order of reflection. The temperature factor corresponds to an estimated characteristic temperature of about 530° The /0-values used are those ofPauling and Sherman1). It is seen that the observed intensity relations (800) (600)... 

Incoming radiation from the Sun and backradiation emitted by Earth interacts with the atmosphere. Although about half of the Sun s radiation passes directly to Earth s surface, a portion is reflected back directly into space, while another portion is absorbed by atmospheric gases and reradiated. Figure 18.3 shows the fate of radiation intercepting Earth. About half of the incoming solar radiation actually reaches the surface of Earth. The rest is reflected or absorbed by the atmosphere or clouds. Infiared radiation reflected from Earth s surface is partially absorbed and reflected by the atmosphere and clouds. Some of this radiation is reradiated back toward Earth s... 

FIGURE 10.8 Changes in the percentage of photosynthetically active radiation intercepted by the foliage of Columbia and Violet de Rennes at 51°58 N. (After Spitters, C.J.T. et al., in Topinambour (Jerusalem Artichoke), Report EUR 11855, Grassi, G. and Gosse, G., Eds., Commission of the European Communities, Luxembourg, 1988, pp. 37-43.)... 

A number of models have been constructed to better understand the development physiology of Jerusalem artichoke. These models quantify the amount of solar radiation intercepted, the efficiency with which light is converted into dry matter, and the distribution of dry matter around the plant over time. Assimilated dry matter is used for structural growth or as storage reserves in different plant parts. 

The acquisition of carbon is strongly modulated by the surface area of photosynthesizing leaves hence, understanding leaf area development is germane to efforts to increase yield. In many crops, biomass is linearly related to the amount of light intercepted (Monteith, 1977). This is certainly the case for Jerusalem artichoke, where total productivity is strongly correlated with the amount of solar radiation intercepted (Denoroy, 1996 Meijer et al., 1993). Leaf area, leaf duration, and photosynthetic efficiency of the crop canopy determine how much light is intercepted and subsequently utilized (Table 10.9). 

Consider a surface different from surface i, say surface j. The total radiation from this surface is Bj Aj. The fraction of this radiation intercepted by surface i is B AjFji, which may be rearranged in terms of the reciprocity relation [Eq. (9.11) for surfaces i and j] AjFji = AiF(j to give BjAiFij. Thus, the total radiation leaving all surfaces (including /) and intercepted by surface i is... 

The Earth s climate is controlled by the amount of solar radiation intercepted by the planet and the fraction of that energy that is absorbed. The flux density of solar energy, integrated... 

Fig. 1. The mean dry weight per unit ground area in relation to the cumulative quantity of visible radiation intercepted by a Z. mays crop in N.E. Essex, England. The broken line is the expected relationship in the absence of any depression in conversion "efficiency".

Some radiation reflected from the sample in the Bjln mode may be lost out of the entrance port when external optics are used or off of the focusing mirror or lens and its support structure when internal optics are used. This effect can result in an error in the measured reflectance. Similarly, for 2nl6 mode reflectometers, the optics used to collect reflected radiation from the sample reduces the radiant power striking the sample and may affect the measured reflectance. If the sample is a Lambertian reflector and the illumination (0/27i) or viewing (2ti/0) is near normal, then the fraction of radiation intercepting the sample optics is given by... 

The observational efficiency advantage of F.T. spectroscopy presumes that detector noise is constant regardless of whether the detector is employed in a grating or F.T. spectrometer. This is true only for low quality detectors. Most high quality detectors, from bolometers in the far I.R. to photo-conductive semiconductor detectors in the mid I.R., near I.R., and visible region, can achieve the "background limited mode", on F.T. spectrometers. In that case it becomes crucial to determine whether the radiation intercepted by the detector is radiation containing spectral information of interest or not. 

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