Outline
   Underwater Optical Communications
       Introduction
       Underwater Channel
       Challenges
   Inter-Satellite Optical Communications
   Satellite-to-Underwater Optical Communications
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         Underwater (UW) Optical Communications
   Modeling the channel is the first step in UW communications
  The channel is completely different from other FSO systems
    The  transmitter  and  receiver  can  be  very  similar  to 
     aforementioned FSO systems
  Ocean water has widely varying optical properties depending 
     on location, time of day, organic and inorganic content, as well 
     as temporal variations such as turbulence and surface motion.
  To construct an optical link it is important to understand these 
     properties.
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                                UW Channel
 The  physical  properties  of  water  is  important  in  modeling  the 
    channel
 Ocean water vary both geographically and vertically with depth
 Geographically  it  changes  from  the  deep  blue  ocean  to  littoral 
    waters near land
  Vertically, the amount of light that is received from the sun is used 
    to classify the type of water.
  The water depth also determines the background radiation from 
    sun light
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                               UW Channel
 The topmost layer is called the euphotic zone and is defined by how 
    deeply photosynthetic life can be found
 Below  this  zone  is  the 
    disphotic zone (1 km deep): 
    the  light  is  too  faint  to 
    support photosynthesis. 
 From  the  lower  boundary 
    of  this  zone  and extending 
    all the way to the bottom is 
    the aphotic zone, where no 
    light   ever    passes    and 
    animals  have  evolved  to 
    take  advantage  of  other 
    sources of food.
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                            UW Channel
 The  various  water  types  are  divided  into  two  categories: 
    oceanic (blue water) and coastal waters (littoral zone).
 The oceanic group is subdivided into 3 groups: Type I-III 
      types I: extremely pure ocean water
     type II: turbid tropical-subtropical water
     type III: mid-latitude water
 The coastal group are subdivided into Types 1 through 9 
  1-9: coastal waters of increasing turbidity
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