Propagation Characteristics Of Laser Beam Traversing The Air-Sea Interface With Foams

With the rapid development of laser technology, the application and research of blue-green laser in the submarine communication have received a wide attention and have become one of the most promising communication technology. The channel of airborne/spaceborne laser communication is composed of three parts: the atmospheric channel, the air-sea interface and the seawater channel. The complexity of the channel is the main limiting factor of laser communication. At present, the research on the characteristics of the channel is mainly concentrated in the atmosphere, the seawater channel, and less involved in the study of the air-sea interface. The study of the scattering characteristics of the air-sea interface is mainly concentrated in the microwave band, which is less involved in the blue- green laser band. So the transmission characteristics of sea suface coverd by foams need to be studied. In this paper, an improved two-scale method is present, which is suitable for calculating the electromagnetic scattering from the sea surface in the visible band. And the transmission characteristics of the blue- green laser in atmosphere near the sea and the rough sea surface covered by foams are studied.In this paper, the basic characteristic parameters of the sea surfaceand the development of sea spectrum in different sea areas are introduced, and the structure of the sea fog and the foam particles are summarized. The simulation of JONSWAP spectrum is carried out by using Monte Carlo method, and the influence of the wind speed and the wind area on the surface fluctuation are verified. Based on the traditional two-scale method, an improved two-sacle method is present, which is suitable for calculating the electromagnetic scattering from the sea surface in the visible band. Then the photon is traced by Monte Carlo method, considering the multiple scattering between photons and fog particles, the transmission characteristics of laser in the sea fog is analyzed and the laser transmittance in the different visibility and distance is calculated. The scattering and transmission characteristics of the blue- green laser in the rough sea surface with foams are studied based on the calculation of the electromagnetic scattering in the microwave band. Using the vector radiative transfer theory, the Mie theory is used to solve the scattering results of a single bubble particle, and then the scattering coefficients of the sea surface with foams are calculated by using the improved two-scale method and the boundary conditions. The influence of wind speed, wind area, and the foam coverage on the scattering and transmission characteristics are analyzed for the Gauss sea surface and the JONSWAP spectrum.The results show that the ability of scattering from air-sea interface in the blue green laser is much weaker than that of the microwave, while the transmission capacity is obviously stronger, and the energy is more concentrated. When the incident angle is large, the small scale wave has obvious enhancement effect on the scattering coefficient in the two bands. The effect of foam particles on the laser scattering and transmission in the blue- green laser band is significantly stronger than that of the microwave.