Definition:
Turbidity is the scattering of light caused by suspended particles in a liquid. The light is dispersed in all directions and partially absorbed by the particles, depending on their size, surface area, and color. The measurement of this phenomenon is known as nephelometry.

Turbidity Units:

• FNU (Formazin Nephelometric Unit): Defined by ISO 7027 using infrared light (860 ± 60 nm) measured at a 90° angle.
• FAU (Formazin Absorbance Unit): Also defined by ISO 7027, using infrared light (860 ± 60 nm) measured at a 180° angle.
• NTU (Nephelometric Turbidity Unit): Defined by EPA Method 180.1, using visible light (tungsten lamp) measured at a 90° angle.
• FTU (Formazin Turbidity Unit): Used when turbidity is measured without a standardized angle.

Correlation with Total Suspended Solids (TSS)
An empirical correlation can be established through laboratory analysis of collected samples :
Total Suspended Solids (TSS) are expressed as mass per unit volume, typically in mg/L or as a percentage (e.g., 100 g/L may correspond to 2, 3, ... or 1000 particles, depending on particle type and distribution). 

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