Underwater optical wireless communications: depth dependent variations in attenuation

Depth variations in the attenuation coefficient for light in the ocean were calculated using a one-parameter model based on the chlorophyll-a concentration C-c and experimentally-determined Gaussian chlorophyll-depth profiles. The depth profiles were related to surface chlorophyll levels for the range 0-4 mg/m(2), representing clear, open ocean. The depth where C-c became negligible was calculated to be shallower for places of high surface chlorophyll; 111.5 m for surface chlorophyll 0.8 < C-c < 2.2 mg/m(3) compared with 415.5 m for surface C-c < 0.04 mg/m(3). Below this depth is the absolute minimum attenuation for underwater ocean communication links, calculated to be 0.0092 m(-1) at a wavelength of 430 nm. By combining this with satellite surface-chlorophyll data, it is possible to quantify the attenuation between any two locations in the ocean, with applications for low-noise or secure underwater communications and vertical links from the ocean surface. (C) 2013 Optical Society of America