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The standard measurement for underwater visibility is the distance at which a Secchi disc can be seen. The range of underwater vision is usually limited by turbidity. In very clear water visibility may extend as far as about 80m, [18] and a record Secchi depth of 79 m has been reported from a coastal polynya of the Eastern Weddell Sea ...
In the expression 6/x vision, the numerator (6) is the distance in metres between the subject and the chart and the denominator (x) the distance at which a person with 6/6 acuity would discern the same optotype. Thus, 6/12 means that a person with 6/6 vision would discern the same optotype from 12 metres away (i.e. at twice the distance).
The PADI recreational dive planner, in "Wheel" format. The Recreational Dive Planner (or RDP) is a decompression table in which no-stop time underwater is calculated. [1] The RDP was developed by DSAT and was the first dive table developed exclusively for no-stop recreational diving. [2]
The human eye is optimised for air vision, and when it is immersed in direct contact with water, visual acuity is adversely affected by the difference in refractive index between water and air. Provision of an airspace between the cornea and the water can compensate, but causes scale and distance distortion.
Bathymetry (/ b ə ˈ θ ɪ m ə t r i /; from Ancient Greek βαθύς (bathús) ' deep ' and μέτρον (métron) ' measure ') [1] [2] is the study of underwater depth of ocean floors (seabed topography), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography.
The vertebrate eye is usually either optimised for underwater vision or air vision, as is the case in the human eye. The visual acuity of the air-optimised eye is severely adversely affected by the difference in refractive index between air and water when immersed in direct contact. provision of an airspace between the cornea and the water can ...
This similarity in refractive index is the reason a diver cannot see clearly underwater without a diving mask with an internal airspace. [3] Absorption of light depends on wavelength, this causes loss of colour underwater. [20] [21] The red end of the spectrum of light is absorbed over a short distance, and is lost even in shallow water. [20]
A bathymetric chart is a type of isarithmic map that depicts the submerged bathymetry and physiographic features of ocean and sea bottoms. [1] Their primary purpose is to provide detailed depth contours of ocean topography as well as provide the size, shape and distribution of underwater features.