For many years sound has been used as a primary method for underwater communication. However, data transmission
rate of acoustic systems is low because typical frequencies associated with underwater acoustics are between tens of
hertz and hundreds of kilohertz. A higher bandwidth can be achieved with visible light to transfer data underwater. The
first challenge for underwater laser communication is scattering and absorption. In addition, there are disturbances
caused by spatial and temporal changes in the water refraction index due to temperature and/or salinity variations.
Optical turbulence, which includes the two effects, is the main theme of this paper. We will discuss the joint IOSB-NRL
experiment whose goal was to test techniques for characterization of underwater optical turbulence and in particular we
will focus on differential motion measurement from an LED array.