Turbidity is the degree to which light is scattered by particles suspended in a liquid, and it is an optical measurement that indicates the presence of suspended particles. Turbidity is often measured relative to water clarity using a Secchi disk, or directly with a turbidimeter or a handheld sensor. There are different methods and instruments used to measure turbidity, and some of them include:
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Transparency tube: This is a visual tool for measuring turbidity, and it is a clear tube with "hatch marks" to measure water depth. The tube is filled with water, and the user looks through it to determine the turbidity.
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Jackson Candle Method: This is a historical method for measuring turbidity, and it involves using a vertical glass tube over a candle. A sample is poured into the tube until the user can no longer see the distinct image of the candle flame. The final height of the sample which was added resulted in the corresponding turbidity measurement.
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Turbidimeter: This is a modern instrument used to measure turbidity, and it consists of a fixed light beam, aperture, and detector. Turbidity meters utilize a light and photo detector to measure light scatter, and read out in units of turbidity, such as nephelometric turbidity units (NTU) or formazin turbidity units (FTU) .
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Turbidity probe: This is another instrument used to measure turbidity, and it is a wide variety of probes available to measure turbidity. The measured turbidity depends on the wavelength of light and the angle at which the detector is positioned. Turbidity probes do not all use the same light sources, angles of measurement to detect the scattered light, and signal processing strategies. As a result, measurements from different makes/models of turbidity probes may not be comparable to one another. To help categorize the differences in turbidity probe design and distinguish among turbidity measurements that may not be comparable, new units of measurement were established in 2004 and assigned based on the probe design.
In summary, turbidity can be measured using different methods and instruments, including transparency tubes, Jackson Candle Method, turbidimeters, and turbidity probes.
