Hybrid phase screen modeling and experimental study of Gaussian beam propagation and imaging under oceanic turbulence

Underwater optical imaging with Gaussian beams offers high resolution and sensitivity, but its performance is significantly affected by oceanic turbulence. Conventional phase screen models lack sufficient physical considerations, which limit their accuracy in predicting beam properties and imaging quality under oceanic turbulence. Here, we present a hybrid random phase screen model that integrates a power spectrum-based approach with the Zernike polynomials method to better represent the entire spatial frequency domain of oceanic turbulence. Numerical simulations are performed to investigate how variations in the mean-square temperature dissipation rate ($X_T$), the kinetic energy dissipation rate ($\epsilon$), the temperature-salinity ratio ($\omega$) and the Kolmogorov microscale length ($\eta$) influence beam propagation and imaging quality. The results demonstrate that stronger oceanic turbulence is governed by the higher values of $X_T$, $\omega$, $\eta$ and lower value of $\epsilon$, resulting in increased beam spot wandering and edge diffusion during propagation, leading to a decrease in central maximum intensity of the beam. Besides, the modulation transfer functions (MTF) of the imaging systems under oceanic turbulence decrease as the values of $X_T$, $\omega$, $\eta$ increase and $\epsilon$ decreases, reflecting the intensified impact of oceanic turbulence. To verify the model, an experimental platform with controlled oceanic turbulence parameters was constructed. The experimental results show good agreement with the simulation results, where the beam exhibits increased wandering and broadening, accompanied by a decrease in peak intensity with increasing temperature gradients, salinity, and injection height. This work provides theoretical and experimental support for evaluating beam propagation and imaging performance in oceanic turbulence.