Seeing Underwater

1
Seeing Underwater

• Objectives of this presentation are to
• learn how light is affected by water
• learn how divers deal with these effects.

2
Light Underwater

• The human eye is made to see in air
• Light meeting the eye underwater is bent
  (refracted) at a greater angle than in air
• The human eye is usually not able to adapt, so
  that a person with 20/20 vision degrades to about
  20/200, which is legally blind.

3
Seeing Underwater with a Mask

• The Skin Diving or Scuba mask restores the air
  around the human eye
• This restores vision to better than normal
• Objects appear about 25 closer
• Objects appear abut 35 bigger
• This occurs because light is refracted (bent)
  twice, once by the water and once by the lens of
  the mask.

4
Seeing Underwater and Water Clarity

• Definition Turbidity-the amount of suspended
  particles in water.
• The particles in turbid water absorb and diffuse
  (scatter) light
• For this reason, a light is worse than useless in
  turbid water
• Extremely turbid water can almost eliminate
  visibility

5
Color Underwater

• Even clean and clear water absorbs light
• Water absorbs different colors at different rates
• The shorter wave lengths are absorbed first
• Most reds and oranges are absorbed in the first
  30 feet.
• Yellows and greens are absorbed by about 60 feet
• Below 60 feet everything is bluish or completely
  grey