Our Senses Underwater
Underwater diving involves having to deal with an environment that is not natural to us and although we take showers, bathe and even go swimming, diving is an entirely different ballgame altogether. Humans are not designed to breathe underwater, and water is significantly different from air. If we don’t understand the principles behind underwater diving, surviving underwater can be a dangerous or even deadly endeavour.
Diving looks easy, right? All you need do is take a tank of compressed air with you, dress in some fancy clothes and done cool goggles and you all good. Not so. Underwater, it’s completely different. Underwater, our senses work differently, the optics under water are different, so we see differently. We hear differently because sound travels much faster. Colours are perceived differently because some are absorbed very differently from how it is absorbed in air. We lose heat faster because water is a much better conductor than air and the pressure underwater is 800 times what is found on land, but since the human body is made up of water mostly, you aren’t in danger of being crushed. However, the gasses inside the body are affected significantly and get compressed a great deal the more you go underwater.
The physics and changes which occur in the human body during underwater diving are numerous, and it will take more than one blog to exhaust them. This particular blog is dedicated to understanding how underwater diving affects vision and hearing.
- LIGHT AND VISION
Underwater, we see differently, and the reason for this relates mostly to physics. The diving mask, with its flat glass lenses, bends light in a way in which the objects underwater are seen as thrice their actual size. However, the magnification varies with the distance between the lens from the eyes and the distance at which an object is. Often, inexperienced divers underestimate the distance of close objects and overestimate the distance of objects which are far away. Unique diving masks are available to eliminate this distortion, but they have some drawbacks and take some getting used to.
Underwater, colours are also different. Colours are wavelengths reflected by an object and underwater, these waves are reflected differently, and some are filtered out by water faster than others. Underwater, lower energy waves are absorbed first, so colour red disappears first, then orange, yellow, green and eventually, blue, this is why everything looks bluer the deeper you go. This sequence applies to a clear water body. In murky waters where there’s less light penetration, things tend to look greenish-yellow.
Also, even under the best conditions, colour can only be seen as far as 100 feet into the water and below that, things start to look black or grey and this affects the quality of water during underwater photography hence a good light source is required for vibrant images. Also, the surface of the water is reflective acts a bit like a mirror so at high noon, with the sun being right overhead, almost all of the sun’s light enters the water. However, at dusk, dawn or late at night, the sun’s rays hit the water at shallow angles, and almost all light is reflected away and doesn’t make it into the water. So you must know that it gets darker faster than you think.
Sound travels four times faster underwater than in air. Underwater, sound is affected by pressure, temperature and salinity and this produces interesting results when sound meets two layers of water with different parameters.
This means that our hearing which is supposed to interpret sound in the air quickly gets confused underwater. Our brain detects the source of the sound and to some degree the distance, of a sound by the difference in its arrival in the right and left ears. With the sound of water underwater being so much faster, our brains can’t process direction of the sound easily, and this makes the sound seem like its coming from all around the diver.