Radiometric Quantities Research Articles

Radiometric Properties of Isothermal, Diffuse Wall Cavity Sources

Total radiant power emission from various diffuse wall cavity sources is calculated without approximation. In addition, a useful radiometric quantity, (o-d), the fraction of blackbody power received by a distant viewer, is precisely defined and calculated. Extensive tabulation of numerical results and tutorial background are included. A new method, faster and more accurate than traditional quadrature methods, for the numerical solution of integral-equations is described in an appendix. Results are applied to the practical problems of cavity design and analysis.

Normalization in Radiometry

When the absolute value X = ?Xmicro(micro).dmicro of incident radiation cannot be obtained from the output V = ?Xmicro(micro) R(x)(micro) dmicroof a selective instrument, with nonuniform responsivity R(x)(micro) = V(micro)(micro)/X(micro)(micro), because the incident distribution X(micro),(micro) is not known, recourse is had to various normalization methods. There is continuing confusion over the significance of a normalized quantity X(n) = V/R(n) and its relationship to the absolute value X. This problem, first discussed for the familiar spectral parameter micro = lambda, is analyzed generally for different normalization methods, in terms of any radiometric quantity X, distributed as Xmicro (micro) identical withdX/dmicro with respect to any radiation parameter a. Peak normalization, most often used, gives conservative, lower-bound values. Bandwidth normalization is also discussed. It is recommended that units for all normalized quantities, such as lumens for photometric quantities, be distinctively designated, e.g., normalized watts or [NW], to emphasize that, without at least the relative incident distribution x(micro) (micro)= X(micro) (micro)/C, they cannot be directly converted to absolute quantities.

Spectroradiometric Characteristics of Natural Light Under Water*

This paper presents spectroradiometric data on the natural radiant flux occurring underwater at three locations in the Gulf of California, in Pacific coastal water near San Diego, and in the plankton-rich water of San Vicente Reservoir (San Diego County). Spectral radiance and irradiance have been measured, and it is shown that under certain circumstances spectral data for these two radiometric quantities are directly proportional. The data have been used to calculate spectral values of the attenuation coefficient and of the reflection function. The various spectra correlate qualitatively with apparent chlorophyll concentration and water color.

Radiance

Wide generality for optical radiometry can be achieved by treating the basic radiometric quantities as field quantities. The treatment is that of classical ray optics, with emphasis on the geometrical relations involved. It is shown that radiance, defined as N ≡ ∂2P∂Ω cosθ∂A [W·cm−2·sr−1], the radiant flux or power per unit solid-angle-in-the-direction-of-a-ray per unit projected-area-perpendicular-to-the-ray, has the same value at any point along this ray within an isotropic medium, in the absence of losses by absorption, scattering, or reflection. More generally, the quantity N/n2 (where n is the index of refraction of the medium) in the direction of a ray is shown to be invariant along that ray, even across a smooth boundary between different lossless media. The usefulness of this invariant property of radiance is illustrated by examples of practical applications.

Radiometric Quantities, Symbols, and Units

Radiometric Quantities, Symbols, and Units