Secchi disk

[shenzhen]

[FONT=&amp]How do you usually evaluate underwater visibility? [/FONT]
We had made a test to use the Secchi disk with a ruler directly underwater.
At first we asked a few divers to evaluate the current visibility by eyes. They estimated it about 60-80% from Secchi.
Now we will make continuous measurements to predict the visibility in the future.
[video=youtube;Uja1Ds34Di4]http://www.youtube.com/watch?v=Uja1Ds34Di4[/video]

 

[spectrum]

I look at it in diver lengths where a diver is something like 7 feet or ~2 meters. At least this provides a yardstick unless solo.

 

[astawowc]

I've heard that some marine biologists were using LEDs directly soldered to 2 x 2AA batteries. During the dark hours, of course. No idea how it compares to Secchi, though.