Menu
Home Explore People Places Arts History Plants & Animals Science Life & Culture Technology
On this page
Radiometry
Techniques for measuring electromagnetic radiation

Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics 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. The fundamental difference between radiometry and photometry is that radiometry gives the entire optical radiation spectrum, while photometry is limited to the visible spectrum. Radiometry is distinct from quantum techniques such as photon counting.

The use of radiometers to determine the temperature of objects and gasses by measuring radiation flux is called pyrometry. Handheld pyrometer devices are often marketed as infrared thermometers.

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.

We don't have any images related to Radiometry yet.
We don't have any YouTube videos related to Radiometry yet.
We don't have any PDF documents related to Radiometry yet.
We don't have any Books related to Radiometry yet.
We don't have any archived web articles related to Radiometry yet.

Radiometric quantities

SI radiometry units
  • v
  • t
  • e
QuantityUnitDimensionNotes
NameSymbol2NameSymbol
Radiant energyQe3jouleJM⋅L2⋅T−2Energy of electromagnetic radiation.
Radiant energy densitywejoule per cubic metreJ/m3M⋅L−1⋅T−2Radiant energy per unit volume.
Radiant fluxΦe4wattW = J/sM⋅L2⋅T−3Radiant energy emitted, reflected, transmitted or received, per unit time. This is sometimes also called "radiant power", and called luminosity in astronomy.
Spectral fluxΦe,ν5watt per hertzW/HzM⋅L2⋅T −2Radiant flux per unit frequency or wavelength. The latter is commonly measured in W⋅nm−1.
Φe,λ6watt per metreW/mM⋅L⋅T−3
Radiant intensityIe,Ω7watt per steradianW/srM⋅L2⋅T−3Radiant flux emitted, reflected, transmitted or received, per unit solid angle. This is a directional quantity.
Spectral intensityIe,Ω,ν8watt per steradian per hertzW⋅sr−1⋅Hz−1M⋅L2⋅T−2Radiant intensity per unit frequency or wavelength. The latter is commonly measured in W⋅sr−1⋅nm−1. This is a directional quantity.
Ie,Ω,λ9watt per steradian per metreW⋅sr−1⋅m−1M⋅L⋅T−3
RadianceLe,Ω10watt per steradian per square metreW⋅sr−1⋅m−2M⋅T−3Radiant flux emitted, reflected, transmitted or received by a surface, per unit solid angle per unit projected area. This is a directional quantity. This is sometimes also confusingly called "intensity".
Spectral radianceSpecific intensityLe,Ω,ν11watt per steradian per square metre per hertzW⋅sr−1⋅m−2⋅Hz−1M⋅T−2Radiance of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅sr−1⋅m−2⋅nm−1. This is a directional quantity. This is sometimes also confusingly called "spectral intensity".
Le,Ω,λ12watt per steradian per square metre, per metreW⋅sr−1⋅m−3M⋅L−1⋅T−3
IrradianceFlux densityEe13watt per square metreW/m2M⋅T−3Radiant flux received by a surface per unit area. This is sometimes also confusingly called "intensity".
Spectral irradianceSpectral flux densityEe,ν14watt per square metre per hertzW⋅m−2⋅Hz−1M⋅T−2Irradiance of a surface per unit frequency or wavelength. This is sometimes also confusingly called "spectral intensity". Non-SI units of spectral flux density include jansky (1 Jy = 10−26 W⋅m−2⋅Hz−1) and solar flux unit (1 sfu = 10−22 W⋅m−2⋅Hz−1 = 104 Jy).
Ee,λ15watt per square metre, per metreW/m3M⋅L−1⋅T−3
RadiosityJe16watt per square metreW/m2M⋅T−3Radiant flux leaving (emitted, reflected and transmitted by) a surface per unit area. This is sometimes also confusingly called "intensity".
Spectral radiosityJe,ν17watt per square metre per hertzW⋅m−2⋅Hz−1M⋅T−2Radiosity of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅m−2⋅nm−1. This is sometimes also confusingly called "spectral intensity".
Je,λ18watt per square metre, per metreW/m3M⋅L−1⋅T−3
Radiant exitanceMe19watt per square metreW/m2M⋅T−3Radiant flux emitted by a surface per unit area. This is the emitted component of radiosity. "Radiant emittance" is an old term for this quantity. This is sometimes also confusingly called "intensity".
Spectral exitanceMe,ν20watt per square metre per hertzW⋅m−2⋅Hz−1M⋅T−2Radiant exitance of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅m−2⋅nm−1. "Spectral emittance" is an old term for this quantity. This is sometimes also confusingly called "spectral intensity".
Me,λ21watt per square metre, per metreW/m3M⋅L−1⋅T−3
Radiant exposureHejoule per square metreJ/m2M⋅T−2Radiant energy received by a surface per unit area, or equivalently irradiance of a surface integrated over time of irradiation. This is sometimes also called "radiant fluence".
Spectral exposureHe,ν22joule per square metre per hertzJ⋅m−2⋅Hz−1M⋅T−1Radiant exposure of a surface per unit frequency or wavelength. The latter is commonly measured in J⋅m−2⋅nm−1. This is sometimes also called "spectral fluence".
He,λ23joule per square metre, per metreJ/m3M⋅L−1⋅T−2
See also:
Radiometry coefficients
  • v
  • t
  • e
QuantitySI unitsNotes
NameSym.
Hemispherical emissivityεRadiant exitance of a surface, divided by that of a black body at the same temperature as that surface.
Spectral hemispherical emissivityεν ελSpectral exitance of a surface, divided by that of a black body at the same temperature as that surface.
Directional emissivityεΩRadiance emitted by a surface, divided by that emitted by a black body at the same temperature as that surface.
Spectral directional emissivityεΩ,ν εΩ,λSpectral radiance emitted by a surface, divided by that of a black body at the same temperature as that surface.
Hemispherical absorptanceARadiant flux absorbed by a surface, divided by that received by that surface. This should not be confused with "absorbance".
Spectral hemispherical absorptanceAνAλSpectral flux absorbed by a surface, divided by that received by that surface. This should not be confused with "spectral absorbance".
Directional absorptanceAΩRadiance absorbed by a surface, divided by the radiance incident onto that surface. This should not be confused with "absorbance".
Spectral directional absorptanceAΩ,ν AΩ,λSpectral radiance absorbed by a surface, divided by the spectral radiance incident onto that surface. This should not be confused with "spectral absorbance".
Hemispherical reflectanceRRadiant flux reflected by a surface, divided by that received by that surface.
Spectral hemispherical reflectanceRνRλSpectral flux reflected by a surface, divided by that received by that surface.
Directional reflectanceRΩRadiance reflected by a surface, divided by that received by that surface.
Spectral directional reflectanceRΩ,νRΩ,λSpectral radiance reflected by a surface, divided by that received by that surface.
Hemispherical transmittanceTRadiant flux transmitted by a surface, divided by that received by that surface.
Spectral hemispherical transmittanceTνTλSpectral flux transmitted by a surface, divided by that received by that surface.
Directional transmittanceTΩRadiance transmitted by a surface, divided by that received by that surface.
Spectral directional transmittanceTΩ,νTΩ,λSpectral radiance transmitted by a surface, divided by that received by that surface.
Hemispherical attenuation coefficientμm−1Radiant flux absorbed and scattered by a volume per unit length, divided by that received by that volume.
Spectral hemispherical attenuation coefficientμνμλm−1Spectral radiant flux absorbed and scattered by a volume per unit length, divided by that received by that volume.
Directional attenuation coefficientμΩm−1Radiance absorbed and scattered by a volume per unit length, divided by that received by that volume.
Spectral directional attenuation coefficientμΩ,νμΩ,λm−1Spectral radiance absorbed and scattered by a volume per unit length, divided by that received by that volume.

Integral and spectral radiometric quantities

Integral quantities (like radiant flux) describe the total effect of radiation of all wavelengths or frequencies, while spectral quantities (like spectral power) describe the effect of radiation of a single wavelength λ or frequency ν. To each integral quantity there are corresponding spectral quantities, defined as the quotient of the integrated quantity by the range of frequency or wavelength considered.24 For example, the radiant flux Φe corresponds to the spectral power Φe,λ and Φe,ν.

Getting an integral quantity's spectral counterpart requires a limit transition. This comes from the idea that the precisely requested wavelength photon existence probability is zero. Let us show the relation between them using the radiant flux as an example:

Integral flux, whose unit is W: Φ e . {\displaystyle \Phi _{\mathrm {e} }.} Spectral flux by wavelength, whose unit is W/m: Φ e , λ = d Φ e d λ , {\displaystyle \Phi _{\mathrm {e} ,\lambda }={d\Phi _{\mathrm {e} } \over d\lambda },} where d Φ e {\displaystyle d\Phi _{\mathrm {e} }} is the radiant flux of the radiation in a small wavelength interval [ λ − d λ 2 , λ + d λ 2 ] {\displaystyle [\lambda -{d\lambda \over 2},\lambda +{d\lambda \over 2}]} . The area under a plot with wavelength horizontal axis equals to the total radiant flux.

Spectral flux by frequency, whose unit is W/Hz: Φ e , ν = d Φ e d ν , {\displaystyle \Phi _{\mathrm {e} ,\nu }={d\Phi _{\mathrm {e} } \over d\nu },} where d Φ e {\displaystyle d\Phi _{\mathrm {e} }} is the radiant flux of the radiation in a small frequency interval [ ν − d ν 2 , ν + d ν 2 ] {\displaystyle [\nu -{d\nu \over 2},\nu +{d\nu \over 2}]} . The area under a plot with frequency horizontal axis equals to the total radiant flux.

The spectral quantities by wavelength λ and frequency ν are related to each other, since the product of the two variables is the speed of light ( λ ⋅ ν = c {\displaystyle \lambda \cdot \nu =c} ):

Φ e , λ = c λ 2 Φ e , ν , {\displaystyle \Phi _{\mathrm {e} ,\lambda }={c \over \lambda ^{2}}\Phi _{\mathrm {e} ,\nu },} or Φ e , ν = c ν 2 Φ e , λ , {\displaystyle \Phi _{\mathrm {e} ,\nu }={c \over \nu ^{2}}\Phi _{\mathrm {e} ,\lambda },} or λ Φ e , λ = ν Φ e , ν . {\displaystyle \lambda \Phi _{\mathrm {e} ,\lambda }=\nu \Phi _{\mathrm {e} ,\nu }.}

The integral quantity can be obtained by the spectral quantity's integration:

Φ e = ∫ 0 ∞ Φ e , λ d λ = ∫ 0 ∞ Φ e , ν d ν = ∫ 0 ∞ λ Φ e , λ d ln ⁡ λ = ∫ 0 ∞ ν Φ e , ν d ln ⁡ ν . {\displaystyle \Phi _{\mathrm {e} }=\int _{0}^{\infty }\Phi _{\mathrm {e} ,\lambda }\,d\lambda =\int _{0}^{\infty }\Phi _{\mathrm {e} ,\nu }\,d\nu =\int _{0}^{\infty }\lambda \Phi _{\mathrm {e} ,\lambda }\,d\ln \lambda =\int _{0}^{\infty }\nu \Phi _{\mathrm {e} ,\nu }\,d\ln \nu .}

See also

References

  1. Leslie D. Stroebel & Richard D. Zakia (1993). Focal Encyclopedia of Photography (3rd ed.). Focal Press. p. 115. ISBN 0-240-51417-3. spectroradiometry Focal Encyclopedia of Photography. 0-240-51417-3

  2. Standards organizations recommend that radiometric quantities should be denoted with suffix "e" (for "energetic") to avoid confusion with photometric or photon quantities. /wiki/Standards_organization

  3. Alternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant exitance.

  4. Alternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant exitance.

  5. Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek letter nu, not to be confused with a letter "v", indicating a photometric quantity.) /wiki/Frequency

  6. Spectral quantities given per unit wavelength are denoted with suffix "λ". /wiki/Wavelength

  7. Directional quantities are denoted with suffix "Ω". /wiki/%CE%A9

  8. Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek letter nu, not to be confused with a letter "v", indicating a photometric quantity.) /wiki/Frequency

  9. Spectral quantities given per unit wavelength are denoted with suffix "λ". /wiki/Wavelength

  10. Directional quantities are denoted with suffix "Ω". /wiki/%CE%A9

  11. Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek letter nu, not to be confused with a letter "v", indicating a photometric quantity.) /wiki/Frequency

  12. Spectral quantities given per unit wavelength are denoted with suffix "λ". /wiki/Wavelength

  13. Alternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant exitance.

  14. Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek letter nu, not to be confused with a letter "v", indicating a photometric quantity.) /wiki/Frequency

  15. Spectral quantities given per unit wavelength are denoted with suffix "λ". /wiki/Wavelength

  16. Alternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant exitance.

  17. Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek letter nu, not to be confused with a letter "v", indicating a photometric quantity.) /wiki/Frequency

  18. Spectral quantities given per unit wavelength are denoted with suffix "λ". /wiki/Wavelength

  19. Alternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant exitance.

  20. Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek letter nu, not to be confused with a letter "v", indicating a photometric quantity.) /wiki/Frequency

  21. Spectral quantities given per unit wavelength are denoted with suffix "λ". /wiki/Wavelength

  22. Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek letter nu, not to be confused with a letter "v", indicating a photometric quantity.) /wiki/Frequency

  23. Spectral quantities given per unit wavelength are denoted with suffix "λ". /wiki/Wavelength

  24. "ISO 80000-7:2019 - Quantities and units, Part 7: Light and radiation". ISO. 2013-08-20. Retrieved 2023-12-09. https://www.iso.org/standard/64977.html