Radiometry

In optics, radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which characterize the light's interaction with the human eye. Radiometry is distinct from quantum techniques such as photon counting.

Radiometry is important in astronomy, especially radio astronomy, and plays a significant role in Earth remote sensing. The measurement techniques categorized as radiometry in optics are called photometry in some astronomical applications, contrary to the optics usage of the term.

Spectroradiometry is the measurement of absolute radiometric quantities in narrow bands of wavelength.[1]

'
Quantity Symbol[nb 1] SI unit Symbol Dimension Notes
Radiant energy Qe[nb 2] joule J M⋅L2⋅T−2 energy
Radiant flux Φe[nb 2] watt W M⋅L2⋅T−3 radiant energy per unit time, also called radiant power.
Spectral power Φeλ[nb 2][nb 3] watt per metre W⋅m−1 M⋅L⋅T−3 radiant power per wavelength.
Radiant intensity Ie watt per steradian W⋅sr−1 M⋅L2⋅T−3 power per unit solid angle.
Spectral intensity Ieλ[nb 3] watt per steradian per metre W⋅sr−1⋅m−1 M⋅L⋅T−3 radiant intensity per wavelength.
Radiance Le watt per steradian per square metre W⋅sr−1⋅m−2 M⋅T−3 power per unit solid angle per unit projected source area.

confusingly called "intensity" in some other fields of study.
Spectral radiance Leλ[nb 3]
or
Leν[nb 4]		 watt per steradian per metre3
or

watt per steradian per square
metre per hertz

 W⋅sr−1⋅m−3
or
W⋅sr−1⋅m−2⋅Hz−1		 M⋅L−1⋅T−3
or
M⋅T−2		 commonly measured in W⋅sr−1⋅m−2⋅nm−1 with surface area and either wavelength or frequency.
Irradiance Ee[nb 2] watt per square metre W⋅m−2 M⋅T−3 power incident on a surface, also called radiant flux density.

sometimes confusingly called "intensity" as well.
Spectral irradiance Eeλ[nb 3]
or
Eeν[nb 4]		 watt per metre3
or
watt per square metre per hertz		 W⋅m−3
or
W⋅m−2⋅Hz−1		 M⋅L−1⋅T−3
or
M⋅T−2		 commonly measured in W⋅m−2⋅nm−1
or 10−22W⋅m−2⋅Hz−1, known as solar flux unit.[nb 5]
Radiant exitance /
Radiant emittance		 Me[nb 2] watt per square metre W⋅m−2 M⋅T−3 power emitted from a surface.
Spectral radiant exitance /
Spectral radiant emittance		 Meλ[nb 3]
or
Meν[nb 4]		 watt per metre3
or

watt per square
metre per hertz

 W⋅m−3
or
W⋅m−2⋅Hz−1		 M⋅L−1⋅T−3
or
M⋅T−2		 power emitted from a surface per wavelength or frequency.
Radiosity Je or Jeλ[nb 3] watt per square metre W⋅m−2 M⋅T−3 emitted plus reflected power leaving a surface.
Radiant exposure He joule per square metre J⋅m−2 M⋅T−2
Radiant energy density ωe joule per metre3 J⋅m−3 M⋅L−1⋅T−2
See also: SI · Radiometry · Photometry
  1. ^ Standards organizations recommend that radiometric quantities should be denoted with a suffix "e" (for "energetic") to avoid confusion with photometric or photon quantities.
  2. ^ a b c d e Alternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant emittance.
  3. ^ a b c d e f Spectral quantities given per unit wavelength are denoted with suffix "λ" (Greek) to indicate a spectral concentration. Spectral functions of wavelength are indicated by "(λ)" in parentheses instead, for example in spectral transmittance, reflectance and responsivity.
  4. ^ a b c Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek)—not to be confused with the suffix "v" (for "visual") indicating a photometric quantity.
  5. ^ NOAA / Space Weather Prediction Center includes a definition of the solar flux unit (SFU).

See also

References

  1. ^ Leslie D. Stroebel and Richard D. Zakia (1993). Focal Encyclopedia of Photography (3rd ed. ed.). Focal Press. p. 115. ISBN 0240514173. http://books.google.com/books?id=CU7-2ZLGFpYC&pg=PA115&dq=spectroradiometry+intitle:%22Focal+Encyclopedia+of+Photography%22#PPA115,M1. 

External links