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- Measuring Clarity
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Measuring Clarity
Clarity is measured using a secchi disk. A secchi disk is a black and white disk attached to a calibrated line. Attach this disk to a line with measurements on it and lower it into a body of water. When the disk is no longer visible, take note of the distance measure on the line. Taking this depth twice and averaging the two values gives you the measure of clarity.
Jackson Candle Method
In the Jackson Candle Method, a cylinder of water is held above a lit candle. The amount of water needed in the cylinder determines the turbidity of the water. The more water needed to block out the light, the less turbid and vice-versa. These amounts are measured in Jackson Turbidity Units (JTU).
Units of Measurement
Lambert-Beer's Law states that three obstacles diminish the light emerging from a sample in a test such as the Jackson Candle Method.
These physical properties are:
1) The concentration of the sediment
2) The distance the light must travel through the sample
3) The probability that the light will be absorbed by the sediment
Absorbance units are expressed as A, AU, or ABS. These are all the same. Concentration Units (CU) or Optical Density (OD) can be measured at various pathlengths. Other units of measurement include Formazin Turbidity Units (FTU), Nephelometric Turbidity Units (NTU), Helms Units, and parts per million.
These physical properties are:
1) The concentration of the sediment
2) The distance the light must travel through the sample
3) The probability that the light will be absorbed by the sediment
Absorbance units are expressed as A, AU, or ABS. These are all the same. Concentration Units (CU) or Optical Density (OD) can be measured at various pathlengths. Other units of measurement include Formazin Turbidity Units (FTU), Nephelometric Turbidity Units (NTU), Helms Units, and parts per million.