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Demonstration of constant radiance for Lambertian Surfaces

I'm approaching to radiometry and I'm struggling with one of the properties of Lambertian surfaces. We know that the radiance is the radiant flux emitted, reflected, transmitted or received by a ...
Mattia's user avatar
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1 answer
32 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} \...
Chris Gnam's user avatar
0 votes
2 answers
70 views

Formal mathematical definition of radiance and irradiance

Radiance is defined as $$L = \frac{\partial^2 \Phi}{\cos{\theta} \partial A \partial\Omega}$$ and irradiance as $$ E = \frac{\partial \Phi}{\partial A},$$ where $\Phi$ is the radiant flux, $\Omega$ is ...
mathslover's user avatar
0 votes
1 answer
86 views

Lambertian surface and the luminous intensity

I am currently studying the basics of photometry to better understand the rendering equation of Kajiya. One thing I'm currently struggling with is Lambert's cosine law. Let's go over the premises: A ...
Bartolini's user avatar
1 vote
0 answers
262 views

Calculate Radiant Intensity from Radiant Power and estimated Radiant Distrubution of infrared LED [closed]

Consider the infrared led TSAL7600 which has the following properties: $$ \Phi = 35 mW $$ $$ I_e = 25 mW/sr $$ The half angle is $30^\circ$ and: $$ I_r(\theta) = cos^{4.818}(\theta) $$ is a good ...
InTheWorks's user avatar
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?
Ocelot's user avatar
  • 111
1 vote
1 answer
148 views

Why does transversal magnetization decay and what is actually being measured in an MRI sequence? [closed]

This may be a few questions disguised as one however this may help uncover what's the missing piece in my understanding. $T1$ characterizes the rate at which longitudinal $M_z$ recovers and $T2$ ...
Ilisuan Iannis Patriciu's user avatar
1 vote
0 answers
137 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 ...
Jbag1212's user avatar
  • 2,589
0 votes
3 answers
519 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 ...
Hakanai's user avatar
  • 123
0 votes
0 answers
56 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 ...
Dinesh Iyer's user avatar
0 votes
0 answers
85 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) = {...
Ken T's user avatar
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1 vote
5 answers
690 views

Are radiance and luminance really independent of distance to observer?

Recently, I learned that apparently both radiance and luminance are independent of the distance between the light emitting object and the observer. The reasoning was that although the radiant/...
tempdev nova's user avatar
1 vote
0 answers
121 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,\...
Marco Toni's user avatar
0 votes
0 answers
50 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? ...
rodm's user avatar
  • 1
1 vote
0 answers
35 views

The Event Horizon Telescope collaboration will announce groundbreaking observations of our galaxy at 12 May 2022, what this announcement could be? [closed]

"Live webcasting for the ESO-hosted EHT 2022 event On 12 May 2022 at 15:00 CEST, the European Southern Observatory (ESO) will host a press conference on groundbreaking new Milky Way results from ...
Markoul11's user avatar
  • 4,155
1 vote
1 answer
204 views

Lambert's cosine law in 3D, why $\cos\theta$ instead of $\cos^2\theta$?

I'm reading the book An Invitation to 3-D Vision and I don't understand a part of the explanation regarding the "basic radiometric image formation model". Looking at the Wikipedia page of ...
Mario Namtao Shianti Larcher's user avatar
0 votes
1 answer
27 views

How can radioactive-dating techniques, such as uranium-thorium analysis, tell you when a human fashioned a tool out of a rock or coral?

This is an archaeology or anthropology question.... Scientists in a recent 'Nature' said they compared recent genetic analyses of theirs, concerning when Polynesian islands were first settled, with ...
Kurt Hikes's user avatar
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1 vote
1 answer
4k views

How to measure luminance of a monitor screen (NITS) with a lux meter (LUX)?

Before you scold me out for using a Lux meter to measure NITs in my screen, let me explain to you the procedure I tried. I basically just need confirmation. I have a Lenovo Thinkvision P32u-10 monitor,...
zeellos's user avatar
  • 19
0 votes
2 answers
2k views

Calculate radiance of Lambertian emitters: Is the solid angle $\pi$ or $2 \pi$?

Given a Lambertian emitter (or reflector) of area $A$ that is emitting a total power (resp. flux) of $\Phi$ (units $W$). To calculate the radiance $L$ (units $\frac{W}{m^2 sr}$) the solid angle $\...
Charles Tucker 3's user avatar
2 votes
0 answers
167 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 ...
imbAF's user avatar
  • 1,396
0 votes
0 answers
87 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 ...
Anning Wuwang's user avatar
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 ...
Rick's user avatar
  • 11
0 votes
0 answers
85 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). ...
Gouz's user avatar
  • 101
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 ...
PerplexedDimension's user avatar
0 votes
1 answer
102 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 ...
PerplexedDimension's user avatar
1 vote
1 answer
724 views

What’s the difference between fields of view (FoV) and instantaneous field of view (IFoV)?

I read that radio telescopes have “huge fields of view (FoV)”, but are unable to precisely localized objects due to their “small instantaneous field of view (IFoV)”. Apparently, somehow the size of ...
PerplexedDimension's user avatar
1 vote
1 answer
179 views

Why do high frequency radio telescope observations require precise localization?

Why do high frequency radio observations, particularly of transient phenomenon such as Fast Radio Burst and Pulsars, require increasingly precise localization with increasingly high frequency?
PerplexedDimension's user avatar
-1 votes
2 answers
948 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 ...
PerplexedDimension's user avatar
0 votes
1 answer
193 views

Is my illuminance calculation correct?

I have been reading about illuminance, illuminous flux, lumens, lux, irradiance, etc on wikipedia. I made this toy problem to test my knowledge. I am posting it here to test if I'm correct. (note, ...
user56834's user avatar
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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 = \...
Sean E. Lake's user avatar
  • 22.6k
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 ...
Edward Vogel's user avatar
2 votes
1 answer
488 views

How do I transform flux density into temperature?

I have flux density data from Planck mission (in Jy) - measure in a certain frequency - and I would like to transform it to temperature data (Kelvin). I'm not sure if I should use Stefan Boltzmann's ...
Luh's user avatar
  • 301
4 votes
1 answer
546 views

Microwaves and Water Molecules: Radar vs Cooking

I am studying microwave radiometry and confused over this apparent contradiction: Microwaves emitted at 2.45 GHz (~15 cm) are absorbed by water molecules, causing the molecules to rotate under the ...
PUNGO9ER's user avatar
3 votes
2 answers
477 views

If two observers look at the same quantum object, will they see the same thing?

Let's say two observers, one at the North pole and one at the South pole, both observe the Moon. Will they see the same Moon, or a subtly different Moon? Intuitively it feels like they should see a ...
Allure's user avatar
  • 21.2k
-1 votes
1 answer
51 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 ...
egor's user avatar
  • 1
1 vote
1 answer
74 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 ...
Sean E. Lake's user avatar
  • 22.6k
2 votes
2 answers
5k views

What does "intensity of light" mean?

In this lecture from MIT, the professor defines the intensity of a wave as the square of the amplitude of the wave. But, at the same time, the professor defines the intensity of light as the number of ...
Michael Chu's user avatar
1 vote
1 answer
3k views

How can I convert spectral irradiance to spectral radiance [closed]

I have information on the spectral irradiance incoming from the sun at the top of the atmosphere in units of $\rm mW\ m^{-2}\ nm^{-1} $. The photons hit a hypothetical surface on the earth with 0.3 ...
Alex Caseiro's user avatar
2 votes
1 answer
244 views

Why do we need to define both luminous intensity and illuminance?

Background If a source radiates $\newcommand{\e}{\mathrm e} \Phi_\e$ total energetic flux (in watts $\rm W$), then it is said to radiate luminous flux $\newcommand{\v}{\mathrm v} \Phi_\v$ defined by ...
gen-ℤ ready to perish's user avatar
4 votes
1 answer
299 views

Obtaining photoelectron counts from known radiance

I am attempting to make a rough estimate of the counts seen on a CCD spectrometer assuming I know the spectral radiance of a calibration source. I understand that this is not the same thing as ...
JN3's user avatar
  • 43
0 votes
0 answers
310 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 ...
gallickgunner's user avatar
1 vote
0 answers
99 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 ...
Peter's user avatar
  • 11
-3 votes
2 answers
339 views

21cm line of Hydrogen spectrum [closed]

What is the advantage that we have when we study about 21cm line of Hydrogen spectrum over others, in radio-astronomy?
Aditya Majali's user avatar
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 ...
user1887919's user avatar
  • 1,731
0 votes
1 answer
2k views

point sources vs extended source irradiance and radiometry question

How can the irradiance of a point source behave proportionally to 1/R^2, where R is the range of the source yet the irradiance of an extended source be independent of range? It doesn't make any sense ...
Jason Scott's user avatar
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 ...
Arka Sadhu's user avatar
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 ...
Josh's user avatar
  • 279
1 vote
1 answer
899 views

Understanding Incident/Exitant Radiance

Reading "Physically Based Rendering", I'm trying to understand what the meaning of the incident and exitant radiance functions. I understand that radiance $L(p,\omega) =\frac{d^2\phi}{d\omega dA^{\...
Ganea Dan Andrei's user avatar
6 votes
1 answer
795 views

Is antenna noise temperature relevant if the physical system temperature is higher?

Assume a lossless antenna connected to a lossy cable at physical temperature 300K. If this antenna is pointed into space, the antenna noise temperature will depend on the brightness temperature of ...
user80551's user avatar
  • 951
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 $\Theta$ ...
MutomboDikey's user avatar