visibility estimation

[tom.bresee]

So as I dive more, I'm trying to write up more accurate and detailed dive reports.
The one thing that seems to be relatively subjective is visibility. Is there an established procedure or protocol for estimating visibility ? If there are two divers, is there an accurate or established manner that most people would agree upon the divers would use to determine the value ?

I know it's a value determined in the horizontal direction, but trying to get a couple ways of determining the actual value. I could go to a platform (or some visual reference) and kick away until I can't see it anymore, etc, just not sure that is correct manner.

 

[musicalmike]

You pose a valid and interesting question. As you mentioned this is completely subjective. Its like asking a fisherman how much their fish weighed. There are many factors that can be used to make a determination. Of course many of these may or not be available to use depending on the type of diving done or the safety involved. I think the best measurement is using the bottom as a reference and knowing the depth. Can you see the bottom from the surface? if you don't have a bottom to reference you can descend and use depth gauge and the surface support as a visual reference. it is much more difficult to accurately determine horizontal visibility unless you carry a tape measure or line reel. I think in general 0-10 bad, 10-20 poor, 20-30 fair, 30-40 decent, 40-50 good, 50-60 very good, 60-70 great, 70-80 excellent, 80-90, superb, 90+ unlimited. I believe visibility is judged both horizontally and vertically and also can change with the depth. So its not uncommon to have a variety of measurements in a single dive.

 

[Croomrider]

50-60 very good, 60-70 great, 70-80 excellent, 80-90, superb, 90+ unlimited.

I think you will really have a hard time distinguishing 10 foot increments over 50 feet. It's all really subjective anyway. What you cal 10-20, someone else may easily call 20-30, or something else. I try to gauge a distance I can make out individual fish of at least a foot.

Mike

 

[Malpaso]

It's fairly easy for me to estimate when I dive in New England, since the distances are so small . I base it on my visual reference of my buddy or buddies. If he is in front of me, How far away are his fins? Can I see anything in front of him? Multiply everything by the length (height) of a person. I always list viz as 6', 12', etc.. Those of you in better conditions don't have it so easy

 

[g1138]

Are you really signalling 500yds from your turn?

It's an estimate. The trick is to get an established reference that you actually know the rough distance to.
Do that over and over again and eventually you'll be able to estimate distance underwater fairly accurately.

If you have a reel or finger spool start by Tying off knots ever 10ft. Then on every dive, spool out 30-40ft and look back; there's your estimates. Recover your line and then enjoy your dive. Eventually you'll be able to visualize those 10ft and better estimate.

For me, I log dives with horizontal visibility and water clarity. I will log vertical visibility as clarity only.
For instance, Murky >10ft; Clear below (Murky above 10ft, clear below).


I had lots of practice when I was spooling out meter tapes for every dive.

 

[NAM001]

All you can do is use what standards you have. can you see your feet then you have >5'. If you were doing some sort of presision mesasurements I suppose you would use a line with knots in it. For normal dive log entry you only have your surroundings. For instance a plane tail wing is 10 ft cause my buddy was over it and the wing was slightly less than twice his body length. from the rudder when he went past the edge of the wing i saw his weight belt but nothing past that. so that would be 10 ft plus 1/2 his heigth. so about 13-15 ft. The more natural the environment is the less knowns you have to work with.

 

[TheRealScubaSteve]

It's fairly easy for me to estimate when I dive in New England, since the distances are so small

Yes, certainly no tape measure required here. I'm not sure they make tapes so small - maybe a sewing tape would be more appropriate. I once had 20-30ft vis at Lane's Cove. If only that was not a once in a lifetime event. . .

 

[Ayisha]

If there is a shipwreck or some other structure and you know how long or wide it is, that can help to figure out the viz.

I don't find the vertical viz to correspond very well with the horizontal viz, especially on a sunny day. I find that just because you can see the surface from whatever depth you're at, doesn't mean that you can see anywhere near as far horizontally.

I also use the heights/lengths of people to figure out how far I can see reasonably clearly.

After the dive, we often discuss what we think the viz was and are usually fairly close in our estimates. If they're different, we end up agreeing on one of the numbers or compromise.

Anything more than 40 or 50 feet, awesome!

 

[emoreira]

The Secchi disk (Secchi disk - Wikipedia, the free encyclopedia) - thanks to TSandM - could be considered the only accurate method to measure the visibility. Though it was defined to measure vertical visibility, it can also be used to measure horizontal visibility, which is more likely what divers meant when speaking about visibility.
The method is too much complicated just to measure visibility. As previously written, estimating visibility as n x body lengths is a good way to do so.

 

[TSandM]

It's your dive log. You can record whatever you want, that makes sense to you.

In my dive log, I record visibility as poor, fair, good, or wow. Poor is where I can't see the bottom until I hit it, and if I persist in the dive, my buddy and I have to rub shoulders to know where one another is. I don't like those dives. I call that viz less than ten feet.

Fair viz is where we can see animals and each other, but have to stay pretty close, and I can get lost because I can't see one landmark from another. I'll dive in those conditions, but I don't like them. That's about ten feet of viz.

Good is where I can relax. I no longer worry about losing my buddy if one of us takes a couple of fin kicks without looking for the other. I can see one landmark from another, so I can navigate without fear of being where I don't intend to be. This is our "good average" viz, about 15 to 20 feet.

"Wow" is where I drop into the water and I can SEE! I can see well beyond my buddy; I can see three or more landmarks at the same time. I can roll over and see the surface from 50 feet or more. Those are amazing days. 30 feet or more of viz.