Talk:Optical depth

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There is a disparity here... I think an optical depth is something like transmission=exp(-depth). But I'm not sure. William M. Connolley 19:54, 1 January 2006 (UTC).[reply]

corrected definition

The optical depth tau is related to the fraction of light scattered. The following equation expresses this relationship:

I/I_0= exp{-tau},

where I_0 is the incident light and I is the light that passes through the medium without being scattered. Equivalently, for a homogenous medium, tau is the ratio of the path length to the mean free path.

Corrected definition inserted in the article, some inexactitudes corrected, some concepts in atmospheric science added. I hope it is appreciated.Marenco 26 September 2006 (UTC)

Great! that's cleared up the definition finally. Deuar 20:13, 27 September 2006 (UTC)[reply]

Cognitive problem with explanation

I think there is a cognitive problem here. As I understand it, optical depth is a property of the material you are looking through, not of you the observer or the object you are observing. However, the article talks about it in analogy to taking an object and moving it backward, which makes it sound like the medium is not what is being described by optical depth.

It might be better to speak of optical depth increasing as the fog gets thicker, and the value of optical depth being the farthest thing you can see through that fog.

Raddick 20:10, 4 November 2007 (UTC)[reply]

I think the explanation can be reformulated to avoid misunderstandings, but is important to state that the optical depth change when there is more medium between the observer and the object (more light get scattered or absorved). So the optical depth is not just a property of the material, but it also depends on the distance between the object and the observer. The farther the object is, the less you see of it (because there is more medium on the way). Hsxavier 23:58, 5 November 2007 (UTC)[reply]

I'm not convinced that the first sentence is correct :

Optical depth is a measure of transparency, and is defined as the fraction of radiation (or light) that is scattered or absorbed on a path.

The equation is correct, but if tau is the fraction of the radiation that is removed then tau=0.5 should mean that half of the radiation has been absorbed or scattered. However e^(-0.5) ~ 0.6 and e^(-1) is certainly not equal to zero. --Maddoug (talk) 15:59, 22 January 2008 (UTC)[reply]

The current (Apr. 25, 2009) first sentence "Optical depth, or optical thickness is a measure of transparency, and is defined as the negative logarithm of the fraction of radiation (or light) that is scattered or absorbed on a path." is not correct. Given I/I0=e^-tau, tau=-ln(I/I0). Thus the first sentence needs to be "Optical depth, or optical thickness is a measure of transparency, and is defined as the negative logarithm of the fraction of radiation (or light) that IS NOT scattered or absorbed (i.e., IS transmitted) on a path." —Preceding unsigned comment added by Random25 (talk • contribs) 18:47, 25 April 2009 (UTC)[reply]