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Radiance, L [W m -2 sr -1] of electromagnetic radiation (ER) (for example, Köhler 1998, Mobley 1994, Morel and Smith 1982, Raschke 1978), also known as sterance (for example, Wyatt 1991), is rhe power of ER, Φ, at a point r in space along a direction, ξ, per solid angle ω(ξ) and per projected area, Ap at r, normal (perpendicular) to that direction (Fig. 1):
| L(r, ξ) = ∂2 Φ / (∂ω ∂Ap) | (1) |
It has been tacitly assumed here that radiance, L(r, ξ), represents an integral over a wavelength range of the spectral distribution (spectrum) of radiance, Lλ(r, ξ) [W sr-1 m-3], where λ is the wavelength of ER.
Radiance is denoted by N in older publications. In the atmospheric optics literature, the radiance is frequently referred to as intensity and denoted by I. This usage of the term intensity conflicts with the radiometric definition of intensity and may lead to confusion, unless the dimension or definition is explicitly stated.
Radiance is a derivative of irradiance, E, with respect to the projected solid angle, Ω (see Eq. 2 in Radiometry: Vector irradiances):
| L(r, ξ) | = ∂E(r, ξ) / ∂Ω | |
| = (cosθ) -1 ∂E(r, ξ) / ∂ω | (2) |
where ω is the solid angle. Radiance is also a derivative of intensity, I, with respect to the projected area, Ap, measured in a plane perpendicular to direction ξ:
| L(r, ξ) = ∂I(r, ξ) / ∂Ap | (3) |
| CITATION: Jonasz M. 2006. Radiometry: Radiance (www.tpdsci.com/Tpc/RdmRadER.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 17-Jan-2006 Modified: 23-Mar-2007 Peer-reviewed: 03-Sep-2006 |
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