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For a laboratory / field test, I'm looking for an easy solution to measure the soil surface elevation. The test runs a flow on a bed. When the erosion takes place the sediment concentration goes high in the water and makes the water unclear. Therefore, the usual laser, infrared, or ultrasonic depth measurement does not doe to high sediment contents. The range of distance between where a device could be mounted and the bed is 15-30 cm. What kind of device can measure a short distance through sedimented water?

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    \$\begingroup\$ Could the lack of water clarity be quantified and used to determine depth? Turn a disadvantage to an advantage? \$\endgroup\$ – Andy aka Mar 4 '15 at 17:34
  • \$\begingroup\$ One method of depth measurement through sludge is high intensity infrasonic (<20 Hz) pulses. A simple method is to use a high intensity square wave through a subwoofer. The suspended particulate matter (SPM) attenuates the higher frequency harmonics of the base frequency, but the lower frequencies typically survive (unless the SPM particles are really large, empirical tests needed) and reflect from the solid surface beneath the sludge. Easy enough to try out in your particular application. \$\endgroup\$ – Anindo Ghosh Mar 4 '15 at 18:50
  • \$\begingroup\$ Thanks @AnindoGhosh for your suggestion. I'm not expert on electronics; is there any commercial device with high intensity infrasonic or should I build mine? Either way, I appreciate if you could hint me where to look for it. \$\endgroup\$ – Mohammad Mar 4 '15 at 20:13
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    \$\begingroup\$ Go old school and drop a hand lead? \$\endgroup\$ – Hauke Holtkamp Apr 22 '15 at 15:58
  • \$\begingroup\$ Hauke's answers may well be the best suggestion. Just because it ended with a question mark doesn't make it not an answer - it was really not proper for a moderator to demote it to a "comment" \$\endgroup\$ – Chris Stratton May 20 '15 at 1:49
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The industrial sensor for sensing the level of sludge in a process tank is an "interface level analyzer". I worked on such a device many years ago, and it did indeed track a muddy layer of sludge 10-20 feet down in a murky sewage settling basin.

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You can always do a physical test. Use a servo which periodically lowers a test object. Measure the object's position directly. Since object will be raised out of the water most of the time, it should not affect your test much.

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