What are the units which I should use for these Rayleigh scattering equations?

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Discussion Overview

The discussion revolves around the appropriate units of measurement for equations related to Rayleigh scattering, as mentioned in a specific article. Participants seek clarification on various constants and values necessary for calculations, including intensity, molecular density, and wavelength.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about the average value and unit of measurement for intensity at the top of the atmosphere for visible electromagnetic radiation.
  • Another participant suggests that the choice of units for intensity can be flexible, as long as consistency is maintained throughout the calculations.
  • A question is raised regarding the use of an RGB color model for intensity values, specifically whether it is necessary to convert these values to a metric intensity unit.
  • Participants discuss the molecular number density and suggest resources for obtaining this information.
  • There is an emphasis on the importance of using consistent units across all variables in the equations to ensure proper cancellation of units.

Areas of Agreement / Disagreement

Participants generally agree that consistency in unit choice is crucial, but there is uncertainty regarding the specific units to use for intensity and whether non-metric units like RGB values are acceptable.

Contextual Notes

Some assumptions regarding the definitions of intensity and the implications of using dimensionless factors remain unresolved, as well as the specific values for constants mentioned in the equations.

Who May Find This Useful

This discussion may be useful for individuals interested in Rayleigh scattering, atmospheric physics, or those working with intensity measurements in various units.

Jonsson
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Hello there,

I am reading this article: http://nis-lab.is.s.u-tokyo.ac.jp/~nis/cdrom/sig93_nis.pdf

After chapter 4.2, it mentions some equations for approximating Rayleigh scattering. That is all well, however, it doesn't mention which units of measurement I should use, nor the value of the constants. This causes problems because I find it hard for me, because I have never worked in the field before.

So,

- What is the average value and unit of measurement for I at the top of the atmosphere for visible electromagnetic radiation?
- K, constant for the standard atmosphere. I could not find this anywhere.
- Molecular density at sea level.
- Wavelength.

Thank you for your time.

Kind regards,
Marius
 
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The units are whatever you wish to use. Looking at say, Equation (1) we notice that the right-hand side is a product of intensity and other variables and functions. Since the left-hand side is intensity too, you can easily see that your choice of units cancel out as long as you remain consistent.

As for the molecular number density, you could probably get it from the table on this page:

http://en.wikipedia.org/wiki/Number_density

As for the rest, they give you the equations to calculate K.
 
Thanks for that.

I am not sure I understand the implications regarding 'remaining consistent', in this case.

Can I for example use an RGB colour model where wavelength 450 is blue, 550 is green and 650 is red, and calculate using intensity at the top of the atmosphere of 255?

Or it is necessary to use a metric intensity unit, and scale the value up to my 8bit 0-255 value?

Which unit do you recommend for intensity?

Thank you for your time.

Kind regards,
Marius
 
Last edited:
Upps, double post. My mistake. I am sorry.M
 
You can use any unit for intensity since the right hand side is intensity multiplied by a dimensionless factor. You input an intensity and get out an intensity. You just need to be consistent in the units you use. If you decide to use meters as you unit of length, then all variables that use length (wavelength, distance) must be in meters so that the units cancel out accordingly.
 
Thank you.

Can you think of a seach phraze which I can type into google where I may find an article explaining the relevance of dimensionless factor?M
 

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