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Unformatted text preview: Click to edit Master subtitle style 9/13/11 ENV 6146, Atmospheric Dispersion Modeling Yi Guo 2011/03/15 9/13/11 Table of Content  General concept (1) What makes a object visible? (2) What makes a plume visible? (3) What cause plume contrast? 9/13/11 WHAT MAKES A PLUME 9/13/11 What Makes a Object Visible Any viewed object is visually perceptible to human observer if the light emanating from the object and impinging on the retina of the eye is sufficiently different from light emanating from other objects so that the difference or contrast between the given object and surrounding objects produce a perceptible signal to the optic nerve and the brain. The most important for visible is contrast 9/13/11 9/13/11 Definition of Contrast C=(I obj-I back )/I back  If contrast>0, object is brighter than background  If contrast<0, object is darker than background 9/13/11 9/13/11 What Cause Plume Contrast? Plume contrast is cause by the decrease or increase in light transmitted from the viewing background through the plume to the observer and this increase and decrease in the light intensity is caused by plume constituents that scatter and/or absorb light b ext = b scat+ b abs b scat ----light scattering coefficient 9/13/11 9/13/11 Plume Effects on Light Transmission  The change in the spectral light intensity at any point along the line of sight: r= the distance along the line of sight from the object to observer =the scattering distribution or phase function for scattering angle Fs( )=solar flux incidence on the atmosphere ( ) ( , ) ( ) ( ) ( ) ( ) 4 est scat s dI p b I b F dr = - + ( , ) p 9/13/11 9/13/11 Two Important Situations in VISCREEN  Plume contrast against the sky  Plume contrast against the terrain 9/13/11 Plume Contrast Against the Sky  I h =Special radiance of horizon sky(without plume present)  I h-plume =Spectral radiance of plume viewed in front of horizon sky  =Average phase function for the plume constituents and the background atmosphere  = average albedo of plume and background, where albedo is the ratio of light scattering to total light extinction  =Plume optical thickness along the line of sight ( 29 ex ( ) [ 1][1 exp ]exp( ) ( ) h plume h plume plume plume t p h background I I pw C b r I pw -- = =---- p plume - 9/13/11 Plume Contrast Against Terrain C r =the sky-terrain contrast of a terrain feature at distance r from an observer...
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This note was uploaded on 09/11/2011 for the course ENV 6146 taught by Professor Staff during the Spring '11 term at University of Florida.

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