PowerPoint Presentation

RADIATION, FLUXES IN THE ENVIRONMENT1BY: PRAKHAR PRASHANT SINGH, RAM SEVAK GUPTA & MOHAN PRAKASHIT REQUIRE AT LEAST 3 STREAMS OUT OF THESE 5 STREAMS:

SP:- DIRECT RADIATION ON THE SURFACE PEERPENDICULAR TO THE BEAM.SD:-DIFFUSE SKY IRRADIANCE ON A HORIZONTAL PLANE.SR:-REFLECTED RADIATION FROM THE GROUND.ST:- TOTAL IRRADIANCE.SB:- BEAM OF IRRADIANCE ON THE HORIZONTAL SURFACE.2ESTIMATING DIRECT AND DIFFUSE SHORTWAVE IRRADIANCE

(SP)3SRSDRELATION BETWEEN THESE TERMS:- SB = SP COS

AND

ST = SB + SD

WHERE IS THE SOLAR ZENITH ANGLE.4SOLAR ZENITH ANGLEThe zenith angle is the angle between the sun and the vertical. The zenith angle is similar to the elevation angle but it is measured from the vertical rather than from the horizontal, thus making the zenith angle =90- elevation.5

IRRADIENCE VS ZENITH ANGLE6

REFLECTED RADIATIONIT IS THE PRODUCT OF THE AVERAGE SURFACE REFLECTED FOR THE SOLAR WAVEBAND AND THE TOTAL SHORTWAVE IRRADIANE OF THE SURFACE:

SR= pSSt

THE SHORTWAVE SURFACE REFLECTANCE IS ALSO CALLED ALBEDO.

7SHORTWAVE REFLECTIVITY(ALBEDO) OF SOILS AND VEGETATION CANOPIES

8ABSORPTIVITIES FOR THERMAL AND SOLAR RADIATONThe absorptivity in a given waveband is equal to the emissivity in that waveband.

ET=Er+Ea+Et

Absorbed energy raised the temperature of body and this energy is emitted latter in formof thermal radiation.9KIRCHHOFFS RADIATION LAW:Absorbed-light(Ea)(Er)(ET)(Et)9

Figure shows the spectral absorptivities of some leaf surfaces in the short-wave region of the spectrum.While all of the surfaces show variation of absorptivity with wavelength,the leaf absorptivity changes dramatically between the visible and near infrared portions of the spectrum.10In the visible, most of the radiation is absorbed, and is used to carry on photosynthesis.Absorption is somewhat lower in the green(around0.55um) part of the spectrum, resulting in green colour of vegetation, but overall,approximately 85% of the incident visible radiation is absorbed while about 15% of the NIR is absorbed.The NIR wavelength are not useful for biochemical processes and are largely reflected or transmitted by the leaf.Since all of the incident radiation is either reflected or absorbed, the absorptivity of these surfaces can be computed as = (1-s) (s=Average short wave refluctance)

11VIEWFACTORS

VIEW FACTOR IS A COMMONLY USED TERM IN ENGINEERINGHEAT TRANSFER AND REFERS TO THE FRACTION OF RADIATION LEAVING ONE OBJECT OF SOME SHAPE THAT IS INTERCEPTED BY ANOTHER OBJECT OF SIMILAR OR DIFFERENTSHAPE.THUS IF AN OBJECT A IS RADIATING AND AN OBJECT B IS RECEIVINGSOME OF THAT RADIATION,THEN THE VIEW FACTOR WOULD BE EXPRESSED AS FA-B.THIS VIEW FACTOR IS GENERALLY DIFFERENTFROM THE VIEW FACTOR FOR RADIATION LEAVING OBJECT B AND RECEIVED BY OBJECT A FB-A.12 Radiation balance

Part of the radiaton on a leaf ,an animal,a crope ,canopy or soil surface is obserbed at the surface.This energy can be warm the surface or be disiplated to the environment or radiaton, Since we are intersted in the energy exchang btw organisms and their sourroundings.The amount emitted is easily computedusing by the Stefan Boltmann equation. The amount obserbed is computed from: Rabs=(FpSp+FdSd+FrSr)+al(FaLa+FgLg)Where,s and l are the absorptivities on the solar and thermal wave bondLa,L are the long wave- flux densities from the atmossphare and the ground Sp Sd Sr are the components of solar radiationFp,Fd,Fr and Fg are view factores btw the surface and the various of radiation

1313The net flux density of radiant energy at a surface aften called net radiation is computed from Rn=Rabs-FesTs4Where:Ts is the surface temp.Fe is the view factor btw the entire surface of the object and the complete sphere of view.14