zondag 11 november 2012

2012-11-11 09:52 The great visibility test

Weather : Clouds with sunshine / SW wind 4 bft / Rain 0. mm / 1011.6 hpa
Divers : Remko, John, Stans, Thijs, Jurre, Koos, Jan, Kacper, Axel
Goal : The Great visibility check
Max depth : 13.4 mtrs
Duration : 63 minutes
Air temp : 11.2 celsius
Water temp : 10,8 celsius minimum
Fish: > only a few young perch between the reedside
Visibility : 7 meters at 3 meter depth 
Remarks: > 15 divers in water.
Today I had asked 7 divers to do a visibility check using the same spool and visibility plate.On this plate you can see both Baseline and Secchi (two white squares) as shown in picture below.
I've used black and white insulation tape because it isn't glossy as laminated ones.
Every diver had to measure 3 times doing:
1-> Baseline meter two outer lines disappear and middle one still visible using lamp (Prescribed method)
2-> Baseline meter three lines disappear using lamp (Alternative method)
3-> Secchi 2 white blocks disappear wihtout using lamp

Of the 7 people the results were pretty constant. I also had asked them to determine which distance was the most realistic in their view.
In general 
1-> at 6,5 -7 meters the divers were still visible (This was considered the most realistic value)
2-> at 8-9 meters the divers began to fade and were not that recognizable anymore
3 -> at 10-11 only the white cylinders were seen but divers were not visible anymore.
On the righthand side you can see the measurements of each diver with the average values.
The lamps did have any effect with the sun shining, although it might give that little extra when it is clouded.

I've done quite a few tests, but never with a group of people this large. I will rest my case and never use anything else again :). I've also corrected the results in my logs.
It is unanimous... Baseline meter gives the best results!

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