<p>A secchi disk is basically a measurement of optical depth, and is very similar in principle to the measurements of AOD made in meteorology.  Those measurements are quantified at a particular wavelength of light (or a few discrete wavelengths), related to the Beer-Lambert law of light extinction.  Light extinction occurs due to scattering and absorption and the total attenuation is integrated.  A nephelometer, in contrast, has it's own light source which is shining on the particles, and a detector measures the reflected light (absorption is not being measured).  The nephelometer is calibrated to measure particle density by volume of a particular type of particle, based on the reflected light signature.</p>

<p><a href="http://en.wikipedia.org/wiki/Nephelometer">http://en.wikipedia.org/wiki/Nephelometer</a></p>

<p><a href="http://en.wikipedia.org/wiki/Secchi_disk">http://en.wikipedia.org/wiki/Secchi_disk</a></p>

<p><a href="http://en.wikipedia.org/wiki/Optical_depth">http://en.wikipedia.org/wiki/Optical_depth</a></p>

CC BY-SA 3.0
2014-11-06T18:14:02.540Z
2014-11-07T06:11:14.917Z
2014-11-07T06:11:14.917Z
f.thorpe
<p>Are measurements for clarity (secchi disk) or turbidity (nephelometer) made for water quality related in any way to measurements made for optical or aerosol optical depth in meteorology?</p>

CC BY-SA 3.0
2014-11-04T14:03:36.047Z
By measurements being related, do you mean measurement methods being related?
milancurcic
CC BY-SA 3.0
2014-11-05T02:34:29.187Z
@IRO-bot I am trying to determine if either of the water quality measurements are the same as atmospheric/cloud measurements made by NASA just in a liquid instead of a gas. The optical (cloud) depth is somewhat confusing for me... something to do with an extinction coefficient. Is this analogous to the measurement of secchi depth after you have lost sight of the disk due to light attenuation? Or does it have more to do with scattering/backscatter of light due to suspended particles? Is optical depth a measure of clarity/transparency or the inverse turbidity?
Steve
<measurements>
Turbidity/clarity vs optical depth
Steve
# Turbidity/clarity vs optical depth

(Asked by: username_0 on 2014-11-04)

Are measurements for clarity (secchi disk) or turbidity (nephelometer) made for water quality related in any way to measurements made for optical or aerosol optical depth in meteorology?

**Tags:** measurements

> **Comments:**
> **username_1**: By measurements being related, do you mean measurement methods being related?  
> **username_0**: @IRO-bot I am trying to determine if either of the water quality measurements are the same as atmospheric/cloud measurements made by NASA just in a liquid instead of a gas. The optical (cloud) depth is somewhat confusing for me... something to do with an extinction coefficient. Is this analogous to the measurement of secchi depth after you have lost sight of the disk due to light attenuation? Or does it have more to do with scattering/backscatter of light due to suspended particles? Is optical depth a measure of clarity/transparency or the inverse turbidity?  

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## 1 answers

### Answer by username_2 on 2014-11-06. Score: 8

A secchi disk is basically a measurement of optical depth, and is very similar in principle to the measurements of AOD made in meteorology. Those measurements are quantified at a particular wavelength of light (or a few discrete wavelengths), related to the Beer-Lambert law of light extinction. Light extinction occurs due to scattering and absorption and the total attenuation is integrated. A nephelometer, in contrast, has it's own light source which is shining on the particles, and a detector measures the reflected light (absorption is not being measured). The nephelometer is calibrated to measure particle density by volume of a particular type of particle, based on the reflected light signature.

<http://en.wikipedia.org/wiki/Nephelometer>

<http://en.wikipedia.org/wiki/Secchi_disk>

<http://en.wikipedia.org/wiki/Optical_depth>


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