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Simulation of the interaction of a high energy laser beam with the sea surface in the short wavelength infrared

: Schwenger, Frédéric; Scherer-Negenborn, Norbert; Braesicke, Katrin


Applied optics 58 (2019), Nr.29, S.8126-8140
ISSN: 0003-6935
ISSN: 1539-4522
ISSN: 1559-128X
Fraunhofer IOSB ()

The knowledge of the interaction of a high energy laser beam with a dynamic sea surface is of great practical interest in maritime environments. The components transmitted into the sea and reflected at the sea surface have to be considered. The calculation of energy transfer into the sea is fundamental to the prediction of upper-ocean heating and temperature-dependent optical properties of the sea, which in turn influence its reflectance characteristics. In addition, the spatial energy (or power) distribution of the laser beam reflected at the dynamic sea surface is also of high significance. For the estimation of the laser light energy reflected into a specific spatial direction, several parameters need to be considered, e.g., wind speed, wind direction, and fetch. The calculated amount of light energy reflected into a specific direction varies statistically and depends largely on the dynamics of the wavy sea surface. A 3D simulation of a dynamic sea surface is presented interacting with a high energy laser beam in the short wavelength infrared spectral band. The simulation computes the upper-ocean heating, the temperature-dependent Fresnel reflectances, and the absorption in seawater considering the laser geometric configuration. For the reflectance calculations, a bistatic configuration of the laser source and receiver is regarded, where the receiver positions are on a virtual hemisphere having the laser spot center as the center point. The specular reflection of the laser beam at the sea surface is modeled by an analytical statistical bidirectional reflectance distribution function of the sea surface. The simulation is restricted to sea surfaces heated to the boiling point to avoid complex phase transition effects between water and gas. For a high energy laser beam focused on a small laser spot on the evolving wavy sea surface, the maximum expected reflected laser power is calculated for the specular forward- and back-reflection direction for glints. The probability of occurrence and temporal occurrence of those glint events is estimated for both directions.