Secchi Disk

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Secchi disk

[′sek·ē ‚disk]
(engineering)
An opaque white disk used to measure the transparency or clarity of seawater by lowering the disk into the water horizontally and noting the greatest depth at which it can be visually detected.

Secchi Disk

 

an instrument for measuring water transparency in a body of water. A white disk 30 cm in diameter, it is held horizontally and lowered into the water on a rope until it is no longer visible. The depth, in meters, at which it ceases to be visible is taken as a measure of the water transparency. The disk is named after A. Secchi, who measured the transparency of sea water by this method in 1865.