Outer scale of the wide-range Prandtl/Schmidt number spectrum on beam wander for oceanic optical turbulence

Abstract

Light propagation in ocean is influenced by the refractive-index which is related to temperature, salinity, outer-scale, etc. Based on Hill's model 1 (H1), two kinds of oceanic refractive-index spectrum (ORIS) have been proposed to describe the second order characteristic of refractive-index. Most recently, several ORIS models were proposed based on Hill's model 4 (H4), which gave a better precision in high wave-numbers (viscous-diffusive range). However, the outer scale, as a key parameter related to practical environment, has not been introduced into any oceanic H4-based spectra. In this paper, we take the outer-scale parameter into an H4-based spectrum which is adapted to the wide-range Prandtl/Schmidt number [Opt. Express. 20, 11111(2019)]. The proposed outer-scaled spectrum could be used in analyzing wave propagation in limited outer-scaled environment with different values of average temperature and salinity. We further derived the beam wander formula of collimated laser beam. Numerical calculations show that the beam wander influenced by outer-scale length $L_{0}$ is more obvious than that influenced by average temperature $\langle T\rangle$, when $L_{0}$ varies from $10 \rm m$ to $100 \rm m$, and $\langle T\rangle$ ranges from $0^{\circ} \rm C$ to $30^{\circ} \rm C$. When salinity fluctuations prevails ($\omega \rightarrow 0$), the influence of outer scale becomes weaker. In contribution proportion of beam wander, the temperature-salt coupling term is the much larger than that of temperature or salinity term.