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Specific (radiative) intensity is a quantity used in physics that describes electromagnetic radiation. It is a term used in much of the older scientific literature. The present-day SI term is spectral radiance, which can be expressed in base SI units as . It gives a full radiometric description of the field of classical electromagnetic radiation of any kind, including thermal radiation and light. It is conceptually distinct from the descriptions in explicit terms of Maxwellian electromagnetic fields or of photon distribution. It refers to material physics as distinct from psychophysics. For the concept of specific intensity, the line of propagation of radiation lies in a semi-transparent medium which varies continuously in its optical properties. The concept refers to an area, projected from the element of source area into a plane at right angles to the line of propagation, and to an element of solid angle subtended by the detector at the element of source area.〔Planck, M. (1914) ''The Theory of Heat Radiation'', second edition translated by M. Masius, P. Blakiston's Son and Co., Philadelphia, pages 13-15.〕〔Chandrasekhar, S. (1950). ''Radiative Transfer'', Oxford University Press, Oxford, pages 1-2.〕〔(Mihalas, D., Weibel-Mihalas, B. (1984). ''Foundations of Radiation Hydrodynamics'', Oxford University Press, New York, ISBN 0-19-503437-6. ), pages 311-312.〕〔Goody, R.M., Yung, Y.L. (1989). ''Atmospheric Radiation: Theoretical Basis'', 2nd edition, Oxford University Press, Oxford, New York, 1989, ISBN 0-19-505134-3, page 16.〕〔Liou, K.N. (2002). ''An Introduction of Atmospheric Radiation'', second edition, Academic Press, Amsterdam, ISBN 978-0-12-451451-5, page 4.〕〔Hapke, B. (1993). ''Theory of Reflectance and Emittance Spectroscopy'', Cambridge University Press, Cambridge UK, ISBN 0-521-30789-9, page 64.〕〔Rybicki, G.B., Lightman, A.P. (1979/2004). ''Radiative Processes in Astrophysics'', reprint, John Wiley & Sons, New York, ISBN 0-471-04815-1, page 3.〕 The term ''brightness'' is also sometimes been used for this concept.〔〔Born, M., Wolf, E. (1999). ''Principles of Optics: Electromagnetic theory of propagation, interference and diffraction of light'', 7th edition, Cambridge University Press, ISBN 0-521-64222-1, page 194.〕 The SI system states that the word brightness should not be so used, but should instead refer only to psychophysics. ==Definition== The specific (radiative) intensity is a quantity that describes the rate of radiative transfer of energy at , a point of space with coordinates , at time . It is a scalar-valued function of four variables, customarily〔〔〔〔Kondratyev, K.Y. (1969). ''Radiation in the Atmosphere'', Academic Press, New York, page 10.〕〔Mihalas, D. (1978). ''Stellar Atmospheres'', 2nd edition, Freeman, San Francisco, ISBN 0-7167-0359-9, pages 2-5.〕〔Born, M., Wolf, E. (1999). ''Principles of Optics: Electromagnetic theory of propagation, interference and diffraction of light'', 7th edition, Cambridge University Press, ISBN 0-521-64222-1, pages 194-199.〕 written as : where: : denotes frequency. : denotes a unit vector, with the direction and sense of the geometrical vector in the line of propagation from :the effective source point , to :a detection point . is defined to be such that a virtual source area, , containing the point , is an apparent emitter of a small but finite amount of energy transported by radiation of frequencies in a small time duration , where : , and where is the angle between the line of propagation and the normal to ; the effective destination of is a finite small area , containing the point , that defines a finite small solid angle about in the direction of . The cosine accounts for the projection of the source area into a plane at right angles to the line of propagation indicated by . The use of the differential notation for areas indicates they are very small compared to , the square of the magnitude of vector , and thus the solid angles are also small. There is no radiation that is attributed to itself as its source, because is a geometrical point with no magnitude. A finite area is needed to emit a finite amount of light. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Specific radiative intensity」の詳細全文を読む スポンサード リンク
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