Unified Modeling of Irradiance Scintillation for Laser Beams in Arbitrary Oceanic Turbulence

Accurate modeling of irradiance scintillation is important for evaluating underwater wireless optical communication (UWOC) systems operating in oceanic turbulence. Existing studies have mainly focused on weak oceanic turbulence conditions, while irradiance scintillation modeling under arbitrary oceanic turbulence strength remains insufficiently developed. In this work, the Gaussian beam is adopted as the representative model of practical laser beams, whereas the plane-wave and spherical-wave cases are introduced as limiting cases to support the derivation and theoretical completeness of the Gaussian-beam formulation. A unified theoretical framework is developed based on the general oceanic turbulence optical power spectrum (OTOPS). Building upon previously reported weak-turbulence results, the scintillation index (SI) under saturated strong turbulence is first derived using asymptotic theory. Then, within the extended Rytov approximation, an effective-scale treatment is introduced to characterize the contributions of large- and small-scale eddies to irradiance fluctuations. By connecting the weak- and saturated-turbulence limits through asymptotic matching, a closed-form SI expression valid over a wide range of oceanic turbulence strengths is obtained. Numerical results show that the proposed model agrees well with the corresponding boundary cases and reproduces the characteristic “bump” behavior of oceanic turbulence, while highlighting the influence of ocean-specific cutoff spatial frequencies on the predicted scintillation peaks. These results provide a physically consistent analytical framework for UWOC channel modeling and performance evaluation under arbitrary oceanic turbulence strength.