Turbidity/clarity vs optical depth 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?
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