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The field of spectroradiometry concerns itself with the measurement of absolute radiometric quantities in narrow wavelength intervals. [1] It is useful to sample the spectrum with narrow bandwidth and wavelength increments because many sources have line structures [2] Most often in spectroradiometry, spectral irradiance is the desired measurement.
Mathematically, for the spectral power distribution of a radiant exitance or irradiance one may write: =where M(λ) is the spectral irradiance (or exitance) of the light (SI units: W/m 2 = kg·m −1 ·s −3); Φ is the radiant flux of the source (SI unit: watt, W); A is the area over which the radiant flux is integrated (SI unit: square meter, m 2); and λ is the wavelength (SI unit: meter, m).
The global irradiance on a horizontal surface on Earth consists of the direct irradiance E e,dir and diffuse irradiance E e,diff. On a tilted plane, there is another irradiance component, E e,refl, which is the component that is reflected from the ground. The average ground reflection is about 20% of the global irradiance.
For propagation of light in a vacuum, the definition of specific (radiative) intensity implicitly allows for the inverse square law of radiative propagation. [12] [14] The concept of specific (radiative) intensity of a source at the point P 1 presumes that the destination detector at the point P 2 has optical devices (telescopic lenses and so forth) that can resolve the details of the source ...
Solar irradiance spectrum above atmosphere and at surface. The overall intensity of solar radiation is like that of a black body radiator of the same size at about 5,800 K. [1] As it passes through the atmosphere, sunlight is attenuated by scattering and absorption; the more atmosphere through which it passes, the greater the attenuation.
Comparison of photometric and radiometric quantities. 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 related quantity spectral radiance is the radiance of a surface per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. Historically, radiance was called "intensity" and spectral radiance was called "specific intensity". Many fields still use this nomenclature.
Radiant intensity is used to characterize the emission of radiation by an antenna: [2], = (), where E e is the irradiance of the antenna;; r is the distance from the antenna.; Unlike power density, radiant intensity does not depend on distance: because radiant intensity is defined as the power through a solid angle, the decreasing power density over distance due to the inverse-square law is ...