Talk:Radiometry

Reflectivity
This article is missing the terms for reflectance/reflectivity. What are they?-69.87.204.232 11:58, 19 May 2007 (UTC)

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Assessment comment
Substituted at 03:49, 30 April 2016 (UTC)

Radimetric measure
On the new radiometer, is it a radiometry understanding that somebody would comment upon here? — Preceding unsigned comment added by 159.100.67.82 (talk) 11:44, 26 August 2018 (UTC)
 * No. We are an encyclopedia. We don't cover new inventions. When it has been written about in reliable, independent sources it may be ready for mention here.--Srleffler (talk) 13:44, 26 August 2018 (UTC)

wavelength/frequency limits
[this repeats a comment left in the topic "irradiance".] for purely instrumental reasons and the relevance of physical quantities to questions that measurement is intended to answer (e.g., astrophysics, climatology, workplace safety regulations, etc.) or measurement location (outer space, earth's surface, etc.), radiology metrics do not routinely include the entire electromagnetic spectrum. this is implied by the vague statement that radiology "measures the electromagnetic spectrum." i believe (but do not have sources to cite) that the routine span of measured irradiance/radiance is roughly the optical range 10e-07 to 10e-03 meters, and i am nearly certain that measures such as the solar constant do not rely on actual instrumental measures in the electromagnetic range 10e-16 to 10e8 ish. they are instead either estimates based on fitting a blackbody curve to the measured segment or overlapping/gappy piece curves estimated from different sources using different instrumentation. this applies to all the subtopics in radiology (irradiance, radiance, etc.) where the wikipedist interest seems fixated on the mathematics at the expense of the practicalities. and while i'm quibbling, a paragraph on the actual instrumentation used would be useful, and place the spectral limits in the context of measurement/observation limitations. Drollere (talk) 15:47, 13 October 2020 (UTC)

Derivative vs. integral relations between radiometric quantities
The figure in this article implies that $$I_{\textrm{e},\Omega} = \frac{d\Phi_{\textrm{e}}}{d\Omega}$$, $$M_{\textrm{e}} = \frac{d\Phi_{\textrm{e}}}{dA}$$, and $$L_{\textrm{e},\Omega} = \frac{dI_{\textrm{e},\Omega}}{dA} = \frac{dM_{\textrm{e}}}{d\Omega}.$$ This seems like an abuse of notation, since $$\Phi_{\textrm{e}}$$ is not actually a function of area or solid angle, and is in fact just a scalar quantity. In reality, accurate relations are surface integrals: $$\Phi_{\textrm{e}} = \iint I_{\textrm{e},\Omega} d\Omega = \iint M_{\textrm{e}} dA$$, $$I_{\textrm{e},\Omega} = \iint{L_{\textrm{e},\Omega}}{dA}$$, and $$M_{\textrm{e}} = \iint{L_{\textrm{e},\Omega}}{d\Omega}$$.

Similarly, the radiant spectral flux can't be defined as the derivative of the radiant flux, since the radiant flux is by definition is not a function of wavelength or frequency. Again, the correct relation is by a definite integral. 65.60.153.214 (talk) 22:25, 30 January 2023 (UTC)
 * It might be an abuse of notation, but it is a well-established one. $$\Phi_{\textrm{e}}$$ is a function if area and solid angle in the sense that the value obtained from the surface integrals depends on the surface over which you integrate. --Srleffler (talk) 06:09, 31 January 2023 (UTC)
 * It is fair to say this notation is well established in the sense that it appears in the literature. For example, The IEV uses this notation in its definitions for radiant intensity, irradiance, and radiant exitance.  What I am unable to find in the literature is a source that explains this notation similar to what can be found in the Leibniz's notation article.  IMO, for this notation to be appropriate for Wikipedia, it needs to be explained---either in the text or via a reference. 65.60.153.214 (talk) 16:39, 3 February 2023 (UTC)
 * I agree that we ought to explain it. Frankly, I found this notation confusing when I first encountered it too. It helps to think about the problem physically, rather than mathematically. You can measure radiant intensity by measuring how much flux passes through an aperture that subtends a particular solid angle, and dividing the amount of flux received by the solid angle subtended. If the source is emitting uniformly in all directions, it won't matter how big the aperture is. If the source's emission is not uniform, however, the amount of flux measured will depend on the direction and the size of the aperture. The "true" intensity in this case is then obtained by using an aperture that is small enough that its size does not affect the result. I read $I_{\textrm{e},\Omega} = \frac{d\Phi_{\textrm{e}}}{d\Omega}$  as shorthand for $I_{\textrm{e}}(\theta,\phi) = \lim_{\Omega \to 0} \frac{\Phi_{\textrm{e}}(\theta,\phi,\Omega)}{\Omega}$, where $θ$ and $ϕ$ are the angular coordinates of the aperture and $Ω$ is the angle it subtends at the source.--Srleffler (talk) 05:36, 5 February 2023 (UTC)

Material properties
More general than the quest for reflectivity this article (and that on photometry) ought to include quantities describing material properties for eg reflexion, scattering, transmission and emission. In radiometry for example BRDF can be used to describe the relation between irradiance and radiance for a surface. BRDF is a multidimensional function describing a large range of conditions. There are probably other quantities of interest too, some relating other quantities to each other, some representing subsets of conditions (e.g. the reflectivity quantity).150.227.15.253 (talk) 15:43, 16 January 2024 (UTC)
 * Sounds like a good idea. Why don't you add some information on that?--Srleffler (talk) 06:50, 17 January 2024 (UTC)