Visability defined

[TexasMike]

Here's a topic I don't think we've discussed before....

We are all used to visibility being one of the statistics on our dive, whether it be 2 feet where I live, or 2 miles where NetDoc lives. More often we hear that it is "10 to 12 feet" or "40 to 50 feet".

But where do you peg the visibility? From where your things begin to dissappear in to the haze? Or where they have completely disappeared?

 

[Dee]

I use where it begins to fade into the haze. If I can't see it well enough to identify it then I don't consider it visible.

 

[TwoBitTxn]

Mike you are asking one of my favorite questions.

I guess one explaination I have that I like is what some people mean when they give a range.

10-15 feet. Ten feet I know what it is. 15 feet its gone

Tom

 

[TexasMike]

Originally posted by Tom Vyles
Mike you are asking one of my favorite questions.

I was actually thinking of our conversation on this from our last CSSP road trip when I posted it. Wanted to get the thoughts of the rest of the group here.

 

[The Chairman]

and how far down you can still see it. I can not remember the diameter of the disk, but 1 or 2 foot comes to mind. This is used quite a bit by those interested in how our lakes are doing here in Mickey Land.

 

[SpyderTek]

Ok, to make matters even more complicated...

When we say, "The Vis is 10 to 15 feet" are we saying wat it is or what we perceive it to be with the 25% magnification?

And what about those of us that require corrective eyewear.?

Since I am not wearing my glasses underwater (I'm near sighted) am I giving a more accurate Vis than a 20/20 person since my poor eyesight makes the 25% magnification my "corrective eyewear" all by itself?


I consider the Vis to be at the point where I can pick my buddy out of a line up of more than one diver. However, I am never sure if I am guess-timating the distance accurately since all the sport fish (bass, trout Etc) appear to me to be at least the length of my forearm!

ST

P.S. forgive spelling errors....didn't feel like running through the spell check today.

 

[CheeseWhiz]

For me, distance is so hard to judge precisely under water, that if I say 50 feet viz, that means + or - 20 feet.

 

[socaldiver]

I normally use a couple of methods to determine the vis. When I first jump in look down to the bottom, when you can see it check your depth gauge and then keep dropping to the bottom to see how far it was. The other method I use is when I am going parallel I fix my sight on the furthest object that is plain to see and count my kick cycle until I get there.

NetDoc, this could be a good Parody. What's vis got to do with it to the Tina Turner tune. Work on it kemosabi.

 

[Walter]

Get or make a secchi disk (Pete, thanks for the spelling). You can make one from the lid of a 5 gallon bucket. Divide it into quarters (with a marker, not a knife) two quarters are painted white (or start with a white lid and save paint) while the other two are painted black. Attach a measuring tape to the center of the disk. One diver swims with the disk. When you can no longer make out the disk, stop. Reel in the tape until it just becomes visible again. Note the measurment on the tape. That is the viz. All else is guess work. Most of my viz reports are guess work. When the VSR team makes grant dives we measure the viz.

DSSW,

WWW™

 

[The Chairman]

Couldn't remember the name of the disk, but it is a Secchi disk! All white for the ocean, white and black for lakes, and all black for streams. Here is an ultra visible URL for your viewing pleasure...

http://dipin.kent.edu/SD Procedure.htm

Now, I know the only procedure needed in a Tejas swamp is how far your hand is in front of you when it disappears, so this is for the rest of us!