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Underwater vision is the ability to see objects underwater, and this is significantly affected by several factors. Underwater, objects are less visible because of lower levels of natural illumination caused by rapid attenuation of light with distance passed through the water. They are also blurred by scattering of light between the object and ...
Visibility, the distance at which objects can be seen in a medium, and illumination, the level of ambient natural of artificial light, are environmental factors which influence the ability of a diver to perform the goal of a dive, and can also strongly affect the safety of the dive.
At sea level, the Rayleigh atmosphere has an extinction coefficient of approximately 13.2 × 10 −6 m −1 at a wavelength of 520 nm. This means that in the cleanest possible atmosphere, visibility is limited to about 296 km. Visibility perception depends on several physical and visual factors.
The environment may affect gear configuration: for instance, freshwater is less dense than saltwater, so less added weight is needed to achieve diver neutral buoyancy in freshwater dives. [115] Water temperature, visibility and movement also affect the diver and the dive plan. [116]
An underwater ecosystem can have high water clarity yet low water quality, and vice versa. Scientists have observed that many lakes are becoming less clear while also recovering from acid rain . This phenomenon has been seen in the northeastern United States and northern Europe.
Open water is unrestricted water such as a sea, lake or flooded quarry, where the diver has unobstructed direct vertical access to the surface of the water in contact with the atmosphere. [6] Open-water diving implies that if a problem arises, the diver can directly ascend vertically to the atmosphere to breathe air. [7]
Several factors influence the diver, including immersion, exposure to the water, the limitations of breath-hold endurance, variations in ambient pressure, the effects of breathing gases at raised ambient pressure, effects caused by the use of breathing apparatus, and sensory impairment. All of these may affect diver performance and safety. [1]
The air flows at the surface are called the polar easterlies, flowing from northeast to southwest near the north pole and from southeast to northwest near the south pole. The outflow of air mass from the cell creates harmonic waves in the atmosphere known as Rossby waves.