Questions tagged [radiometry]
The radiometry tag has no usage guidance.
31
questions with no upvoted or accepted answers
6
votes
3
answers
151
views
What is the radiation field of a black body with temperature $T$ translating at speed $v$?
Suppose I have a spherical black body at temperature $T$ with radius $R$. When stationary in a vacuum at zero Kelvin, it produces an incoherent radiation field according to Planck's law
$$
B_\nu = \...
- 22.5k
3
votes
0
answers
139
views
Energy dependence of integrating dosimeters
The graph shows the relative response of a dosimeter at different energies, normalized to 1.25 MeV Co-60 gamma rays. Curve A is the graph of the equation
$$
\frac{\bigg(\frac{r}{X}\bigg)_\bar{E}}{\...
- 95
2
votes
0
answers
415
views
Why do some materials follow Lambert's cosine law?
I perfectly understand Lambert's cosine law, so I can apply it, it isn't really that hard (now that I got it :)
$$I_n=I_\theta*\cos\theta$$
What I don't understand is why some materials follow this ...
- 216
1
vote
0
answers
19
views
How to obtain mass attenuation coefficients of a compound given mass attenuation coefficients of separate elements?
Given a table of MACs for each element, like this one, is it possible to obtain a MAC for a chemical compound or solution? If so, how do I obtain one?
- 111
1
vote
0
answers
126
views
Spectral Irradiance of a Blackbody
This website states that the spectral irradiance of a Black Body is
$$F(\lambda) = \frac{2 \pi h c^2}{\lambda^5 (\exp (hc/k\lambda T)-1)}.$$
What does it mean to talk about "the" spectral ...
- 2,306
1
vote
0
answers
113
views
Relation between Radiance and Surface power density (i.e poynting vector intensity)
I am attending a microwave remote sensing course and I have same problem to understand the relation between the radiance and the intensity of poynting's vector.
The radiance is defined as:
$L(\theta,\...
- 11
1
vote
0
answers
155
views
Difference between radiant power and radiant flux
In Wikipedia the definition of radiant flux is: radiant energy per unit of time.
(deriving w.r.t area you get the radiant exitance or radiant emittance).
So this means that the radiant flux is the ...
- 1,344
1
vote
0
answers
28
views
Brightness Temperature layered atmosphere
I'm trying to figure out how to apply the radiative transfer model to calculate the brightness temperature Tb in microwave (Rayleigh–Jeans approximation) considering atmosphere and no scattering.
If I ...
- 11
1
vote
0
answers
23
views
How is VLBI delay calculated, practically?
I’m working on a research project wherein we are trying to solve a problem very similar to VLBI delay. We have two radio receivers, and we know their locations. We also know at what time one receiver ...
1
vote
1
answer
47
views
Irradiance Measurement of Incandescent Lamps
I have two spectroradiometers that use the same detector from two different manufacturers an Oceaan Optics FX and a Gamma Scientific GS1220. They each have their own cal lamps.
After calibrating ...
- 11
1
vote
1
answer
70
views
How do I translate between spectral radiometric quantities and electromagnetic ones?
In the study of electricity and magnetism we learn that light is just a series of waves in the electromagnetic field. We learn about the Poynting vector
$$\mathbf{S}=\mathbf{E}\times\mathbf{H},$$
the ...
- 22.5k
1
vote
0
answers
98
views
Is power received reflected off a surface dependant on both the incident and emitted angles?
I am trying to calculate the incident power into a detector as reflected from a small illuminated Lambertian surface. Basically I am looking for a check of my calculations as I am not confident that ...
- 11
1
vote
0
answers
58
views
Radio vs X-ray pulsar timing
The detection and timing of pulsars is a common goal in astronomy (eg.1, 2).
Typically these observations are done in the radio. I appreciate that observations are taken in the X-ray as well, but is ...
- 1,709
1
vote
0
answers
61
views
Does a (tungsten-halogen) calibration lamp keep calibrated if unused over a period of several years?
We have a calibration lamp at work that is NIST traceable. It's a tungsten-halogen source that's used for radiometric measurements, so we have a table of power per wavelength. These lamps typically ...
- 269
1
vote
0
answers
161
views
radiance at a grazing angle
I was analyzing radiance equation, i.e. $L = \frac{\partial\Phi}{\partial\Omega \partial A \cos\Theta}$ and judging by the equation it appears that radiance just blows up as the angle $\Theta$ ...
- 23
1
vote
0
answers
69
views
Geometric and radiometric distribution of light
I'm studying the behavior of the light in a scene, to know how much light arrives at a specific point of a surface and how much of it leaves from the point.
From the documentation I'm reading, it says ...
- 111
1
vote
0
answers
172
views
Hemisphere irradiance
How do I calculate sky irradiance from radiance (L) from a hemisphere above a surface which is tilted relative to the normal (x=0,y=0,z=1). I have L as a function of zenith (0 to 180deg) and azimuth (...
- 11
0
votes
1
answer
28
views
Calculating radiance
I'm trying to understand how to calculate radiance ($L_{e,\nu}$), so I am using the sun/earth as a comparison as I have seen it stated that the radiance of sunlight is equal to:
$$
L_{e,\Omega} \...
- 203
0
votes
0
answers
51
views
Irradiance from balloon onto sensor
I am new to radiometry and some of the concepts are confusing me. I want to calculate the irradiance on a sensor from a balloon which is half illuminated by the sun and half illuminated by diffuse ...
- 274
0
votes
3
answers
456
views
Is this how to compute radiance for a point light source? How does this equation work?
I'm writing a ray tracer. Assumptions which led to this point:
Rays are in units of spectral radiance (watts per steradian per square metre) - this appears to be correct based on the subsequent maths ...
- 123
0
votes
0
answers
53
views
What do the CIE Standard Illuminants SPDs represent?
The CIE publishes the relative SPD for standard illuminants. I was curious what photometric quantity it represents i.e. radiance or irradiance or something else.
I was reading the "Intro the ...
- 113
0
votes
0
answers
83
views
Does radiant flux depend on solid angle?
I learned from various sources (e.g. Wikipedia) that the radiant flux $\Phi$ is the radiant energy emitted, reflected, transmitted, or received per unit time and is defined by:
$$\Phi(\mathbf{x},t) = {...
- 145
0
votes
0
answers
49
views
What is the irradiance of an extended source?
For example, what is the irradiance at a certain A = 2m^2 surface from a P = 10W tube lamp with significant radius and length - say, r = 15mm L = 100mm - measured at a small distance - say, d = 2m? ...
- 1
0
votes
0
answers
84
views
Radiance definition
I have been trying very hard to get my head around how the radiance definition is illustrated on the web.
Every website puts the apex of the solid angle on the surface, but the definition said the ...
- 101
0
votes
0
answers
81
views
How does Tx Power affect the Free Space Path Loss model?
On this website one can use the FSPL model to calculate the Path Loss. This is typically interpreted online as the theoretical signal strength (in dB) that one may receive (e.g. from some WiFi). ...
- 101
0
votes
1
answer
96
views
What is the “single pulse radiometer equation”?
This document https://arxiv.org/abs/1601.03547 refers to the “single pulse radiometer equation”. Apparently, it’s used to calculate the flux of radio transients. What is the “single pulse radiometer ...
0
votes
0
answers
306
views
How is radiance conserved? - Power/intensity misconception
Before getting to the main question I'd like to clear some pretty basic concepts regarding energy/power/intensity as my physics is pretty rusty.
According to wiki
In radiometry, radiant flux or ...
- 153
0
votes
1
answer
1k
views
Radiance calculation for extended spherical light source
I have a spherical light source of radius R. There is a surface patch of area $\delta A$ located at a distance $d$ from the spherical source. How do I calculate the scene radiance due to surface patch ...
0
votes
1
answer
114
views
A few questions about the definition of the BRDF
Hi everyone (I'm sorry for my bad english)
I was reading the book "Physically-based rendering" and I came across the definition of the BRDF :
$ f(x,\theta, \psi) = dL(x\rightarrow\theta)/dE(x\...
-1
votes
2
answers
887
views
How is interferometry used to measure distances?
I understand how a basic interferometer works, and how Michaelson used an interferometer to more-or-less disprove the “luminiferous anther”, but, analytically, how would one go about using an ...
-1
votes
1
answer
50
views
Why are CIE standard illuminant SPDs given as relative power?
Why is CIE standard illuminant data given as relative power distribution, and not absolute? They are always normalized, usually so that the power at 560nm is 100. Seems like an unnecessary loss of ...
- 1