Environ Remote Sensing
Environ Remote Sensing ERS 186
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Dan Skiles IV
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Popular in Environmental Resource Science
Dan Skiles IV
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This 15 page Class Notes was uploaded by Dan Skiles IV on Tuesday September 8, 2015. The Class Notes belongs to ERS 186 at University of California - Davis taught by Staff in Fall. Since its upload, it has received 22 views. For similar materials see /class/187674/ers-186-university-of-california-davis in Environmental Resource Science at University of California - Davis.
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Date Created: 09/08/15
Summary of Radiometric Terms Radiant ux W the amount of radiant energy emitted transmitted or received per unit time Radiant ux density Wmz radiant ux per unit area Irradiance Wm2 radiant ux density incident on a surface Radiant spectral ux density W m392 pm39l radiant ux density per unit of wavelength interval Radiant intensity Wsr ux emanating om a surface per unit solid angle Radiance W m392 sr39l radiant ux density emanating om a surface per unit solid angle Spectral radiance W m392 sr391 pm39l radiance per unit wavelength interval Radiant emittance Wmz radiant ux density emitted by a surface Summary of radiometric terms Radiant energy J l Add time Radiant ux J S W Hemispherical Directional dd area Add direct Radiant ux denSity Wmz Radiant intensityWsr Irradiance incident Add area Radiant emittance emitted Radiance W m392 srl Add wavelength Add wavelength Spectral radiance Radiant spectral ux W m z srl um 1 density W m392 um39l Re ectance terms Bi directional re ectance the ratio of the re ected radiance from a single view direction to the irradiance from some incident view direction that is con ned to a very narrow range of incident angles Directional hemispherical re ectance the ratio of the re ected radiance integrated over the entire view hemisphere to the irradiance from a single view direction con ned to a narrow range of incident angles Hemispherical directional re ectance ratio of the re ected radiation from a single view direction to the incident irradiance averaged over the entire incident hemisphere Bi hemispherical re ectance the ratio of the re ected radiance integrated over the entire view hemisphere to the incident irradiance averaged over the entire incident hemisphere of incoming radiation Bi directional re ectance factor is the ratio of the re ected radiance from a single view direction to the re ected radiance from an ideal perfectly diffuse surface experiencing the same irradiance reference panel The Cosine Law M MOCOSQ Where M0 is the ux density normal to the beam M is the ux density at the surface and 6 is the angle between the radiant beam and a normal to the surface Which is referred to as the zenith angle Irradiance For isotropic radiation With radiance of L radiance is constant across all incident directions in the hemisphere 27 2 E zL E L1 s1n6cos6d6dw7rL Where 6 is the zenith angle and w is the azimuth angle Thus the irradiance of a surface under isotropic radiation is always 7r times the radiance Radiation Components Ea L Di Lsf f 4 I I I l u I 1 I I l 4 I l l l 39 l 1 y I I 391 39 x I l 39I I 391 r 1 I w u 4 a I f A quotI m Surface re ected Unscattered Downscattered Pathscattered Radiation Components S su Sd Sp L L L L Surface Re ected Unscattered Component E2 Is the top of atmosphere irradiance It can be calculated using Plancks blackbody equation and a few geometrical terms It varies by only a couple of percent depending on the distance between the sun and earth E1 Is the irradiance at the surface of the earth and is dependent on the solar path atmospheric transmittanceTS as well as the zenith angle6 by way of the cosine rule Emav Ts1E36059xy Surface Re ected Unscattered Component The solar path atmospheric transmittance TS is the variable difficult to determine It is a function of the distance the solar beam travels through the atmosphere which is a function of the solar zenith angle 6 as well as atmospheric parameters which in uence scattering absorption and transmittance There are complex radiative transfer programs available to determine it such as MODTRAN They require estimates of atmospheric parameters such as water vapor content aerosol content etc to be used Surface Re ected Unscattered Component After calculating the irradiance at the earths surface the next energy transfer occurs upon re ectance with a surface material The irradiance downward onto a Zambertz an surface is converted to the radiance leaving the surface with the aid of a geometric factor 7r E Llx9y 10x9y9 7I Surface Re ected Unscattered Component Now we must account for the radiance leaving the surface and traveling through the atmosphere once again towards the sensor L3 gong Thus the total surface re ected unscattered component is W 239 1239 1E0 L2 Pxay91 V 7 2 cos 6x y Radiation Components Ea L Di Lsf f Surface re ected Unscattered Downscattered Pathscattered Surface Re ected Atmospheric Down scattered Component Why are shadows not completely dark Because of diffuse radiation scattered downwards by the atmosphere S TV xi Ed Lid Fx9ypx9yalamp Where F is the fraction of the sky hemisphere which is Visible from the pixel of interest and E2 is the diffuse sky irradiance Radiation Components Ea L Di Lsf f 4 I I I l u I 1 I I l 4 I l l l 39 l 1 y I I 391 39 x I l 39I I 391 r 1 I w u 4 a I f A quotI m Surface re ected Unscattered Downscattered Pathscattered Path Scattered Component The path scattered component is a function of the amount of Rayleigh Mie and nonselective scattering in the atmosphere It is highly dependent on wavelength It is assumed to be constant over a scene and can be determined using radiative transfer models