Radiometric concepts
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Radiometric Concepts. Remote Sensing ERAU Dr. Darrel Smith September 30, 2008. Outline. Radiometric Terms Blackbody radiation Inverse-Square Law for Irradiance Lambertian Surfaces. Radiometric Terms. Irradiance (E) --flux per unit area onto a surface

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Radiometric Concepts

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Radiometric concepts

Radiometric Concepts

Remote Sensing

ERAU

Dr. Darrel Smith

September 30, 2008


Outline

Outline

  • Radiometric Terms

  • Blackbody radiation

  • Inverse-Square Law for Irradiance

  • Lambertian Surfaces


Radiometric terms

Radiometric Terms

  • Irradiance (E) --flux per unit area onto a surface

  • Radiant Exitance (M)--flux per unit area away from the surface.


Radiometric terms1

Radiometric Terms

  • Radiant Intensity (I) --describes the angular distribution of the flux from a point source.

  • The “radiance” (L)--provides both angular and spatial information about the flux from a point source.


Blackbody radiation

Blackbody Radiation

  • Blackbody spectrum -- Planck (1901)Emissivity () -- ratio of the spectral exitance to the exitance from a blackbody at the same temperature.

  • 0 <  < 1


Blackbody radiation1

Blackbody Radiation

  •  = constant describes “gray bodies”

  •  = varies with  describes “selective radiators”


Transmission reflection absorption

Transmission, Reflection, Absorption

  • Transmission ReflectionAbsorptionConservation of Energy

Note: Kirchoff’s law  = 


Properties of blackbody radiation

Properties of Blackbody Radiation

  • Calculate the “total exitance” from a blackbody radiator.where  = 5.6710-8 W/(m2K4)

  • Peak of the blackbody exitance (Wien’s Law)where A = 2898 mK

Note: 10 m window at T = 300K


Homework problem

Homework Problem

  • What fraction of the spectral radiant exitance M is in the visible spectrum (400 nm 700 nm) for the sun?Assume a temperature of 5800 K.


Stealth technologies

Stealth Technologies

  • How does stealth technology work?

  • Reduce the RCS (Radar Cross Section)

    • Choice of angles

    • Materials that act like a blackbody


Lambertian surfaces

Lambertian Surfaces

  • How is the energy leaving a surface angularly distributed into the hemisphere above the surface?

  • A lambertian surface has the following property:

  • How is the radiance angularly distributed from a Lambertian surface? Note: the visual response is proportional to the radiance.


Lambertian surfaces1

Lambertian Surfaces

  • The radiance along the normal from a Lambertian surface will be:The radiance into any direction  from the normal is:Combining the previous 3 equations, we obtain:


Lambertian surface

Lambertian Surface

  • Note: Since perceived brightness is proportional to the radiance in the visible region, this means that a Lambertian surface would look the same from all direction.

  • While we cannot assume that all surfaces are Lambertian, it is a good starting point for discussion of less well-behaved surfaces.


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