Today I decided to complete some more research about Turbidity and the issues surrounding this topic. Using http://water.usgs.gov/osw/techniques/TSS/ZieglerT.pdf I have written a brief summary of my understanding of the article (see below):
Turbidity Definition:
Turbidity can be defined as a decrease in the
transparency of a solution due to the presence of suspended and some dissolved
substances, which causes incident light to be scattered, reflected, and contracted rather
than transmitted in straight lines; the higher the intensity of the scattered or attenuated
light, the higher the value of turbidity.
Turbidity can be expressed in nephelometric
turbidity units (NTU). Depending on the method used, the turbidity units as NTU can be
defined as the 'intensity of light at a specified wavelength scattered or attenuated by
suspended particles or absorbed at a method-specified angle, usually 90 degrees'.
Issue Relating to Turbidity Measurement:
Different Turbidity methods, standards, reporting of units, and
instruments are not identical meaning that because turbidity is an
apparent optical property of water, it is likely that dilution of samples would not result in
a physically reproducible measurement.
Light
wavelengths are different, and color can affect the measurements. Different instruments
may use forward or backscatter detection devices and multiple incident light sources and
detection devices at different orientations that can compensate for the effects of color and
grain size. Therefore, measurements of the same
water by different methods and different instruments are not likely to produce similar values.
The color of water can cause a negative bias in measurements by constricting the light in
colored samples. The color of the darkened sediment particles has been shown to substantially
affect measurements with optical backscatter meters, and it is expected that
nephelometers would give a similar negative bias in measurements depending on the minerals in the sediment .
All turbidity meters can be
affected by the grain size and orientation of the sediment in a sample liquid.
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