Visibility under water

The underwater visibility is an important environmental influence on all kinds of underwater activities . When scuba diving or snorkeling is often from the point of view speaking, when the sight is meant. Since light is more strongly absorbed by water than by air , visibility in water is generally less than above water. The range of vision can have a great influence on the ability to spatial orientation , the possibilities of nature observation , the success of underwater recordings and also on the psychological perception.

Light in the water

Schematic representation of the color absorption in water

The absorption of the water is strongest in long-wave light . The strong absorption of the red light becomes noticeable as a bleaching from a depth of just a few meters. At a depth of around 10 meters, red is no longer perceptible. With greater depth, colors appear more and more bluer, as an ever larger part of the spectrum is filtered out. Darkness prevails from 60 meters at the latest, as the blue short-wave light cannot penetrate that far through the water. This process is known as extinction in technical terms .

The same light absorption happens not only from top to bottom, but also across the water surface, which means that the visibility under water is basically limited to a maximum of 60 meters. In practice, however, the visibility is usually less. If a diving lamp is used, the visual range corresponds to half the light range. The light emitted by the lamp must first reach the illuminated object through the water. There it is reflected and goes the same way back to the diver's eye. So it covers the same distance twice. The water absorbs the light on the way there and back.

Masks and glasses

With direct contact between the eye and water, a large part of the refraction of light on the outer surface of the eye lens is eliminated . Since the human eye is optimized for seeing in the air, the adaptability of the eye lens is no longer sufficient to focus properly underwater. That is why it is impossible to see clearly underwater without a diving mask - which significantly limits the range of vision that can be used. Through a diving mask or swimming goggles, there is no water on the eye, but air. The additional refraction at the outer curve of the eye lens, through which sharp vision with the human eye is only possible, is restored. Because of the refraction of the light on the mask glasses (water-air transition) everything appears around 33 percent larger and 25 percent closer than the brain is used to from overwater.

Visibility in normal cases

Depending on the type of body of water , the visibility under water is very different. In swimming pools filled with drinking water , it is possible to see 40 meters or more. The same applies to clear tropical waters or very cold mountain lakes. The visibility in ocean water is usually good in the temperate or subtropical climate zone. Visibility ranges of 10 to 20 meters are possible here. Visibility can change very quickly in inland lakes. It can range from under 10 centimeters to 25 meters. In moor lakes , visibility is usually poor to very poor. 10 centimeters to a few meters are normal in boggy water.

Influences on visibility

Particles floating in the water reflect the light and cast a shadow on the background.

fauna and Flora

A few meters of visibility in a freshwater lake.

The fauna and flora in the water have a major influence on the visibility in the water. If the water is very rich in nutrients, it contains a lot of plankton and algae . They produce excrement and their death creates suspended particles that float in the water. These living beings - which are often a little larger or smaller than a millimeter - scatter and reflect, together with the suspended particles, the light and thus, like droplets of mist in the air, obstruct the view.

Large amounts of pollen from land plants can also be washed into the water and reduce visibility.

Different types of water

Large amounts of precipitation or tributaries in a body of water can cause a layer of clear water to form over the murky water. This often happens where fresh meets salt water or where water of different temperatures flows together. At the often clearly visible layer boundary, the range of vision can change dramatically from one meter to the next.

Weather

In addition to the precipitation, which can clear up a lake or fjord in the upper meters, the wind has a great influence on the visibility. The waves created by the wind can mix cloudy and cold water in such a way that ultimately everything is cloudy. The silt from the bottom of the water is often churned up by the waves near the shore , which can greatly increase the number of suspended particles in the water.

season

Very good visibility in the shallow tropical salt water

The visibility can vary greatly depending on the season . In winter, visibility is usually better in Central European waters than in midsummer. Because of the lower water temperatures in winter, there are fewer living things floating in the water. In spring, the view can be much clearer or much more cloudy due to large amounts of water from the snowmelt, depending on the geology and size of the catchment area of the water body concerned. In autumn, the view slowly clears up in many bodies of water, as the life cycle of many living things slowly approaches the winter low point.

Geographical location

The geographical location at which the underwater activity takes place can also be decisive. Visibility can vary greatly locally, especially in larger bodies of water. Tributaries that carry a lot of bed load or flow through a bog can locally restrict the visibility. There are also a number of anthropogenic causes for changes in visibility under water. In the vicinity of large settlements or when there is intensive agriculture nearby , the plankton and algae develop much more strongly. Certain branches of industry, such as mining , which discharge cloudy wastewater into the watercourse, can also contribute to poor visibility locally. Construction work on or in the water has the same effect.

Influences on deep-sea inhabitants

In the low-light deep sea , influences can be observed on the animal world due to the underwater visibility, which is dependent on the wavelength of the light. While many deep-sea dwellers have transparent or dark bodies to camouflage themselves in this low-light habitat, some deep-sea dwellers, such as the vampire squid and the giant squid, have a very noticeable red color above water. The subordination of the deep-sea frogfish contains transparent, black and red species. Although the color red over water is often used as a signal color , it has exactly the opposite effect in the low-light area of the deep sea. Since red light is most strongly absorbed under water and does not penetrate into these depths, this color offers camouflage. The deep sea is dominated by deep blue light. Most deep-sea dwellers specialize in seeing blue or bluish-green light. These short wavelengths have the greatest range underwater. Small amounts of residual light can even penetrate to a depth of 1000 meters.

swell

^ ^A ^b ^c Thomas Kromp , Hans J. Roggenbach , Peter Bredebusch : Practice of diving : 3rd edition. Delius Klasing Verlag, Bielefeld 2008, ISBN 978-3-7688-1816-2 .

↑ ^a ^b Diving Physics - Light & Seeing ( Memento of the original from August 16, 2013 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Andreas Nowotny, accessed 12 February 2013. @1@ 2

↑ Deadly red in the deep sea: color pulses. Retrieved November 30, 2019 .

[Praxis_des_Tauchens-1] A ^b ^c Thomas Kromp , Hans J. Roggenbach , Peter Bredebusch : Practice of diving : 3rd edition. Delius Klasing Verlag, Bielefeld 2008, ISBN 978-3-7688-1816-2 .