Aperture Averaged Scintillation of Gaussian Beam in Strong Oceanic Turbulence

Oceanic turbulence caused by salinity and temperature fluctuations underwater affects the characteristics of a transmit laser beam resulting in turbulence-induced intensity fluctuations (i.e., scintillation) at the receiver. Oceanic optical wireless communication (OOWC) systems employ a receiver lens of aperture to focus the collected light onto a photodetector. This way, aperture averaging takes place and the scintillation on the detector is reduced. Using the modified Rytov theory, aperture averaged scintillation of the Gaussian beam passing through strong oceanic turbulence is examined in this study. Effects of Gaussian beam parameters and the turbulence parameters on the aperture averaged scintillation and the aperture averaging factor are illustrated. The scintillation behaviors of the limiting cases of a spherical wave and a plane wave are also reported. Results show that aperture averaged scintillation decreases with increasing the size of the receiver aperture for any turbulence level. The effect of Gaussian size on the aperture averaged scintillation varies depends on the turbulence level. It is also shown that there is a close match between the point scintillation index values obtained from the modified Rytov theory and the conventional Rytov theory in low levels of turbulence.