ch5: radiative properties of natural surfaces
DESCRIPTION
- PowerPoint PPT PresentationTRANSCRIPT
![Page 1: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/1.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
CH5: Radiative Properties of Natural Surfaces
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
![Page 2: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/2.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
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
![Page 3: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/3.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
More Details on the Polarization States
Circular Polarization
Elliptical Polarization:
The most general representation.
![Page 4: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/4.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
Fresnel Reflection Coefficients: What is the magnitude of the light specularly reflected from an ice surface as a function of wavelength?
Medium 2
Medium 1
i
t
![Page 5: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/5.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
Here assume n1=n1r, n1i=0, n2=n2r, n2i=0.
MIRAGES
n1sin(1)= n2sin(2)
For a gas, (nr-1) ≈ =gas density.
d/dz > 0 for this type or mirage.
What does this say about the likelihood of convection?
z
Another type of reflection without a real interface.
Mirages can complicate the BRDF
![Page 6: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/6.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
Solar Wavelengths: Reflection + Absorption = Total Radiation
Incident = 1
Reflection = r()
Transmission = Absorption = a()
1 = a() + r()
![Page 7: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/7.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
Radiant Intensity and Flux: How do we deal with reflected radiation?
What are examples of each type of reflection?
![Page 8: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/8.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
Reflection is Complex !!!
![Page 9: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/9.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
Reflection Coefficient of Various Surfaces
Notes: 1. Snow varies greatly with wavelength, especially in the IR.2. Note the straw versus alfalfa (dry dead plant versus live plant).
![Page 10: CH5: Radiative Properties of Natural Surfaces](https://reader036.vdocuments.net/reader036/viewer/2022062409/5681514c550346895dbf6cf2/html5/thumbnails/10.jpg)
Pat Arnott, ATMS 749 Atmospheric Radiation Transfer
General Case: BDRF BRDF, Bidirectional Reflection Function.
Special Case: Lambertian Surface.
General Case: Why the cos and sin?
General Case: reflectivity