Defining visibility

[Bob DBF]

Does that mean "see" another diver? Or that you see a blur that MAY be a diver?

I'd say it's the distance you can recognize it's a diver, a blur doesn't help you spot your buddy. My problem is estimating in clear water, since I'm in it so little.

 

[johndiver999]

It is quite common to have multiple layers of water and each layer has a different clarity. Horizontal and vertical visibility is often very different from each other. When I estimate visibility, I am trying to describe horizontal visibility. When it is clear and I am talking about vertical vis, it is nice to report top to bottom, meaning I can see clear distinction between dark and light materials from the surface.

Physical oceanography is most concerned with vertical visibility since this is related to light penetration and the consequent potential for photosynthesis; I think anyway. I estimate horizontal visibility as distance I can clearly see a diver, but I can often detect a stream of bubbles from a greater distance than I can make out the diver. At night, a light shined from a distance toward my eyes can be seen considerably farther than what I would describe the visibility to be.

 

[BoltSnap]

Horizontal and vertical visibility is often very different from each other.

Exactly! When you, as a diver, look up towards the surface, you're looking towards the light source and hence better visibility in contrast to horizontal visibility at depth where there is less light than the surface and suspended particulars/turbidity reduce the horizontal visibility to less than vertical visibility.

I have frequently dove in places 50 meters or more in depth where I can see the boat on the surface but horizontal visibility is cloudy and can't see the entire wreck that I know is less than 30 meters long.

 

[apedai]

I decide use rank record the visibility crystal-acceptable-bean soup-sewage

 

[SlugLife]

Interesting question from my daughter filling her dive log after a dive.

She asked me what the visibility was today and I told her 30 feet ish.

She then asked me how I determined that - I was stumped - I just said I thought I could clearly make out stuff at 30 feet or so away.

Is there an actual technical definition of visibility?

I'm attaching a picture from the dive.

Your definition is essentially accurate. It's all a guestimate.

To be honest, we're probably also wrong much of the time, due to refraction distorting what your eyes see. For example, have you noticed fish appear bigger underwater or you try to do a swim-under, think you have plenty of space and bump into it anyway?

I suppose we could actually measure visibility, but who has time for that? At the end of the day 5-inches, 5ft, 10ft, 20ft, 30ft, 60ft, etc are all decent ballpark figures.

 

[AnnoyedSpelunker]

Distance or depth perception underwater is generally faulty with your naked eyes.
I generally shine the torch beam directly in front of me and observe how far the beam penetrates the water. If the beam only penetrates a short distance, I deduce the visibility is poor. This has worked great for me till now

 

[icechip]

I gauge it by the distance I can recognize my buddy, especially with the viz challenges in Maine waters. 15ft is a good day.

 

[happy-diver]

Visibility is when divers, and non divers, and divers pretending to be divers, and non divers pretending to be divers
set up an easy interesting interaction almost like groupies, and all to while the afternoon away with friendly chatter

"How's the vis!"