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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 ...
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### 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/...
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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: $L(\theta,\... 0 votes 0 answers 50 views ### What is the irradiance of an extended source? For example, what is the irradiance at a certain A = 2m^2 surface from a P = 10W tube lamp with significant radius and length - say, r = 15mm L = 100mm - measured at a small distance - say, d = 2m? ... • 1 1 vote 0 answers 35 views ### The Event Horizon Telescope collaboration will announce groundbreaking observations of our galaxy at 12 May 2022, what this announcement could be? [closed] "Live webcasting for the ESO-hosted EHT 2022 event On 12 May 2022 at 15:00 CEST, the European Southern Observatory (ESO) will host a press conference on groundbreaking new Milky Way results from ... • 4,155 1 vote 1 answer 204 views ### Lambert's cosine law in 3D, why$\cos\theta$instead of$\cos^2\theta$? I'm reading the book An Invitation to 3-D Vision and I don't understand a part of the explanation regarding the "basic radiometric image formation model". Looking at the Wikipedia page of ... 0 votes 1 answer 27 views ### How can radioactive-dating techniques, such as uranium-thorium analysis, tell you when a human fashioned a tool out of a rock or coral? This is an archaeology or anthropology question.... Scientists in a recent 'Nature' said they compared recent genetic analyses of theirs, concerning when Polynesian islands were first settled, with ... • 4,479 1 vote 1 answer 4k views ### How to measure luminance of a monitor screen (NITS) with a lux meter (LUX)? Before you scold me out for using a Lux meter to measure NITs in my screen, let me explain to you the procedure I tried. I basically just need confirmation. I have a Lenovo Thinkvision P32u-10 monitor,... • 19 0 votes 2 answers 2k views ### Calculate radiance of Lambertian emitters: Is the solid angle$\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$\...
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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 ...
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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 ...
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### 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 ...
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### 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). ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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?
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### 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 ...
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### 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, ...
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### 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 ...
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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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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?
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### 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 ...
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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 ...
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### 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 ...
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