Optical depth
Dimensionless measure of radiant power attenuation through a material.
Last updated
The ratio of incident to transmitted radiant power, when expressed as a natural logarithm, defines the optical depth.[1] When optical depth is larger, the fraction of radiant power that passes through a material is reduced.[1] Although optical depth grows as the path length through a medium increases, it is a dimensionless quantity and not a physical length.[1]
Quick Facts
- Field
- Physics
- Related quantity
- Absorbance (decadic absorbance) in chemistry
Facts from the source article.
Key facts and history
Spectral optical depth can be expressed in terms of frequency (τ_ν) or wavelength (τ_λ).[1] In atmospheric science, the optical depth with respect to height within the atmosphere is given by τ(z) = k_a w_1 ρ_0 H e^{-z/H}.[2] The total atmospheric optical depth is given by τ(0) = k_a w_1 ρ_0 H.[2] With fixed depth and total liquid water path, τ is proportional to N^{1/3}.[3]
The symbol τ represents optical depth, which is calculated as the natural logarithm of the incident radiant flux divided by the transmitted radiant flux.[4]
What the research sources say
The book "A first course in atmospheric radiation" by Petty, published by Sundog Pub. in 2006, provides the formulas for atmospheric and cloud-layer optical depth.[5][2][3]
References
- Wikipedia, "Optical depth" (CC BY-SA 4.0) en.wikipedia.org
- Wikipedia, "Optical depth" (CC BY-SA 4.0), which cites: Petty, "A first course in atmospheric radiation", Sundog Pub, 2006; Petty, "A first course in atmospheric radiation", Sundog Pub, 2006 (we also read that source) en.wikipedia.org
- Wikipedia, "Optical depth" (CC BY-SA 4.0), which cites: Petty, "A first course in atmospheric radiation", Sundog Pub, 2006 (we also read that source) en.wikipedia.org
- Wikipedia, "Optical depth" (CC BY-SA 4.0), which cites: Christopher Robert Kitchin, "Stars, Nebulae and the Interstellar Medium: Observational Physics and Astrophysics", CRC Press, 1987 (original not read by us) en.wikipedia.org
- Open Library record, ISBN 9780972903318 ("A first course in atmospheric radiation"). CC0 (metadata); book content not read. openlibrary.org
Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Optical depth (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.
More in Optics And Photonics
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Optical depth (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced