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### 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 ...
1 vote
99 views

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 ...
43 views

### Calculating the solar constant using Radiance

I'm looking to calculate the radiance of the sun for use in a ray tracer. I figured a useful way of checking that I did this correctly would be to multiply the radiance value by the solid-angle ...
1 vote
16 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?
1 vote
20 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 $T2$ ...
52 views

### Conversion of luminous flux to optical power in Watt from OSRAM datasheets with normalized relative spectral emission curves

I have in my DLP projector RGB-LED's. I want to compare the optical power of the three LEDs but the datasheet for the blue LED states the radiant power in Watt and the green and red LED in luminous ...
55 views

### How to justify the equation for the field scattered from a surface appearing in Beckman and Spizzichino's book on rough surface scattering?

The formulas in question are (11) and (12) from Section 3.1 page 20 of Beckmann and Spizzichino "The Scattering of Electromagnetic Waves from Rough Surfaces" (I'm looking at the 1987 version ...
41 views

### Isotropic Radiation and Lamberts Cosine Law

Suppose I have a cavity with electromagnetic energy density $u_v$. This may depend on temperature and frequency, like in a Black Body for example; i.e., $u_v = u_v(\nu, T).$ The radiation inside the ...
1 vote
85 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 ...
187 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 ...
36 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 ...
63 views

1 vote
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### 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 ...
344 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 ...
444 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 ...
357 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 ...
47 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 vote
57 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 ...
4k 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 ...
2k views

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 ...
210 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 ...
264 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 ...
276 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 ...
1 vote
95 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 ...
312 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?
1 vote
55 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 ...
2k views

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 ...
968 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 ...
1 vote
55 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 ...
1 vote