Question: Can you relate Secchi disk measurements to turbidity sensor measurements?

wmacfarl is asking a question about water-quality: Follow this topic

by wmacfarl | October 28, 2019 15:13 | #21317


You can take turbidity measurements of liquids using turbidity sensors such as this (which essentially shine a light through a known amount of the liquid at a light-sensor and measure how much light gets through.)

You can also take turbidity measurements using your eyeballs with a tool like a Secchi disk. With the Secchi disk you drop the disk into your liquid and measure how deep it goes before you can't see it.

Secchi disk measurements will presumably vary based on the amount of ambient light in the area where you are taking your measurement, as well as based on the eyesight of the measurer, so I guess there probably can't be a precise "Secchi depth to NTU" conversion.

But I don't know how significant this variability is -- does anyone know if there is an imprecise but "close-enough" conversion factor, or any other good way to think about comparing data collected through these two different techniques?



7 Comments

The digital sensor tell the turbidity by measuring how much of a known light intensity reaches its light sensor in a known amount of liquid and its calibration data is saved in a computer memory and every sensor is different and must be individually calibrated. The Secchi desk works in a slimier way except our eyes are the light sensor and the calibration data is in a notebook, every human is different and its better to have your own notebook.

The easiest solution I would think of in case you are taking outdoors measurements. Always take the readings at the same time of the day, 12 pm for example, write down the full date and weather conditions including the sky clarity and then write down the measurements. Then compare the readings from the calibrated digital sensor with the Secchi readings in your notebook "Your analog calibration". Later while taking your regular readings try to be in the same conditions like your past calibrated readings.

Digital sensors wear out and need calibration periodically as specified in their datasheet same as using the Secchi under the sun. Depending on where you live, you will need to compare your data with a calibrated digital sensors every x months according to the position of the sun in the sky and the time of the year.

Reply to this comment...


We shared this question on our social media and received these responses

Is this a question? Click here to post it to the Questions page.

Is this a question? Click here to post it to the Questions page.


Is this a question? Click here to post it to the Questions page.


Is this a question? Click here to post it to the Questions page.


Is this a question? Click here to post it to the Questions page.


Is this a question? Click here to post it to the Questions page.


Reply to this comment...


Log in to comment