Quiz - Physics - Visual Reversal
- Thread starter Pedro Burrito
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"Visual Reversal" is a topic that is covered in the PADI material, as a way of describing items under water looking further away due to turbidity in the water. Not sure I'd consider it unreasonable for a PADI test to use the terminology they introduce in their educational material.
No different than SSI referring to dive gear as your "total dive system."
No different than SSI referring to dive gear as your "total dive system."
It looks like you were responding to my comment...
I meant the quotes to mean the concept of objects seeming to be further away, rather than the literal phrase. My comment was that I can't find any reference in the SSI materials that I have access to that refer to the phenomenon at all, regardless of phraseology. I looked at the OW, Night & Limited Vis, and SOD stuff and didn't see any reference to it. I don't have my PADI OW stuff from a million years ago so I couldn't check it. I don't remember ever being taught such a thing.
Does anyone have an explanation for this phenomenon?
It's very closely related to "aerial" or "atmospheric" perspective out of the water (note that these are not PADI terms); objects that are further away are interpreted as such due to a loss in optical clarity, luminosity, and contrast. When you look at a mountain that is far away, you judge it as further away because it's hazy and harder to pick out details.
Underwater, suspended particles amplify this effect, so objects that have reduced optical clarity, luminosity, and contrast due to turbidity in the water are interpreted as further away.
This is a perceived reversal from objects looking physically larger due to refraction; hence "visual reversal".
Nirvana
Contributor
I had never heard of "visual reversal" before seeing this thread. After googling the meaning, I am left unconvinced that there is any value in using this expression, as it does not seem to be widely used and does not clearly convey its meaning.
I thank @Pedro Burrito , though, for once again bringing up a topic of discussion for the community.
I thank @Pedro Burrito , though, for once again bringing up a topic of discussion for the community.
Nirvana
Contributor
Are you asking me?
I think that we don't need a name to every single difference in perception that occurs underwater. There are several differences, some of which have been object of previous questions on this series (loss of red color and difficulty determining the direction of a sound source come to mind). If we were to come up with an obscure name for every one of them, I think we would unnecessarily complicate things.
I don't think it's unreasonable to teach divers that depth perception underwater is distorted with closer objects seeming closer and further away ones seeming even further, particularly at the DM level where navigation and s&r skills are expected.
Nirvana
Contributor
Sure, teaching that is useful. But it does not require creating a name for the phenomenon that is not shared by the scientific community or the rest of the diving community.
I thought that might be the answer.
Now clearly, this explains how we are able to judge relative distances of two mountains of differing distances sitting in our field of view. Is PADI asserting that turbidity FOOLS us into thinking that objects are actually further away than we think they are? Being fooled into thinking an object is closer than reality is the point to discussing refraction. Our well developed intuition for judging distance based on our stereoscopic vision is confounded by refraction as experienced underwater. Is there a similarly confounded expectation regarding turbidity? (Sorry, haven't seen the PADI info to read up on it myself)
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