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CH5: Radiative Properties of Natural Surfaces

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CH5: Radiative Properties of Natural Surfaces

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  1. BRDF: One of the most general means to characterize the reflection properties of a surface is by use of the bi-directional reflection distribution function (BRDF), a function which defines the spectral and spatial reflection characteristic of a surface. The BRDF of a surface is the ratio of reflected radiance to incident irradiance at a particular wavelength: L = reflected radiance (radiant intensity) and E is the incident irradiance (flux). From http://math.nist.gov/~FHunt/appearance/brdf.html CH5: Radiative Properties of Natural Surfaces

  2. Polarization States: A reminder Wave/Photon boson: Polarization. Linear Polarization: E-field in one direction. Circular, elliptical polarization: E-Efield rotates due to phase difference between horizontal and vertical components. From: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polclas.html

  3. More Details on the Polarization States Elliptical Polarization: The most general representation. Circular Polarization

  4. Fresnel Reflection Coefficients: What is the magnitude of the light specularly reflected from an ice surface as a function of wavelength? i Medium 1 Medium 2 t

  5. Mirages can complicate the BRDF Here assume n1=n1r, n1i=0, n2=n2r, n2i=0. Another type of reflection without a real interface. n1sin(1)= n2sin(2) MIRAGES z For a gas, (nr-1) ≈  =gas density. d/dz > 0 for this type or mirage. What does this say about the likelihood of convection?

  6. Solar Wavelengths: Reflection + Absorption = Total Radiation Incident = 1 Reflection = r() Transmission = Absorption = a() 1 = a() + r()

  7. Radiant Intensity and Flux: How do we deal with reflected radiation? What are examples of each type of reflection?

  8. Reflection is Complex !!!

  9. Reflection Coefficient of Various Surfaces Notes: Snow varies greatly with wavelength, especially in the IR. Note the straw versus alfalfa (dry dead plant versus live plant).

  10. General Case: BDRF BRDF, Bidirectional Reflection Function. General Case: Why the cos and sin? Special Case: Lambertian Surface. General Case: reflectivity

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