The “blue–green window” in the ocean plays an important role in functions such as communication between vessels, underwater target identification, and remote sensing. In this study, the transmission process of blue–green light in the upper ocean is analyzed numerically using the Monte Carlo method. First, the effect of total number of photons on the numerical results is evaluated, and the most favorable number is chosen to ensure accuracy without excessive costs for calculation. Then, the physical and mathematical models are constructed. The rough sea surface is generated under windy conditions and the transmission signals are measured in the far field. Therefore, it can be conceptualized as a 1D slab with a rough boundary surface. Under windy conditions, these bubbles form layers that are horizontally homogeneous and decay exponentially with depth under the influence of gravity. The effects of bubble populations on the process of blue–green light transmission at different wind speeds, wavelengths, angle ...

The influence of bubble populations generated under windy conditions on the blue–green light transmission in the upper ocean: An exploratory approach

Considering the scattering and absorption caused by seawater molecules and suspended particles, the characteristics of blue-green laser in seawater are described. Then a transmission model of blue-green laser in shallow seawater is established and the relations of the attenuation of received power and the requisite transmission power to the transmission distance are summed up. Results of the simulation experiment are obtained and it can provide references for engineering estimation.

Researches on underwater transmission characteristics of blue-green laser

Seawater is a complex multicomponent system, which involves varieties of organic, inorganic, dissolved and suspended substances. However, the main components dissolved in seawater are the inorganic salts such as NaCl, MgCl2, KCl, NaHCO3, and MgSO4. These elements make different contributions to the spectra of absorption and scattering in water. In this paper, the spectra of different aqueous solutions were measured in the region from 200 to 1200 nm; the attenuation characteristics of aqueous solutions were studied at wavelengths of 450, 532, and 633 nm, respectively; the relationships between attenuation coefficient and the conductivity in different concentrations were also studied.

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Research on the attenuation characteristics of some inorganic salts in seawater

Developing a mathematical model for the dielectric properties of water over a wide range of frequencies helps design, develop, model and optimize processes involving the interaction of electromagne...

Modeling the very broad band dielectric properties of water

An externally-heated, longitudinally-discharged, low-repetition-rate copper bromide laser, was designed and fabricated. The green-coloured wavelength at 5106 A from this laser can be used for underwater ranging and detection of submerged objects. Several new changes in the design of discharge tube, heating technique, buffer-gas-flow sub-system and electrical circuit have been conceived and incorporated advantageously in our system. Various parameters, for example, the type of buffer gas and its flow rate, mixture of gases, temperature of the discharge tube, delay between dissociation and excitation pulses, dissociation and excitation energies, and various resonator configurations are being optimised to get the maximum output power/energy from the laser system.

https://publications.drdo.gov.in/ojs/index.php/dsj/article/download/4332/2535

Design and Fabrication of Externally-heated Copper Bromide Laser

A review of the present knowledge about the origin of blue-green window in the attenuation spectrum of ocean waters is presented. The various physical mechanisms which contribute to the formation of the w-indow are dealt separately and discussed. The typical values of attenuation coefficient arising out of the various processes are compiled to obtain the total beam attenuation coefficient. These values are then compared with measured values of attenuation coefficient for ocean waters collected from Arabian sea and Bay of Bengal. The region of minimum attenuation in pure particle-free sea water is found to be at 450 to 500 nm. It is sbown that in the presence of suspended 'particlesand chlorophyll, the window shifts to longer wavelength side. Some suggestions for future work in this area are also given in the concluding section.

R. Krishnamohan

Papers

The Origin of Blue-Green Window and the Propagation of Radiation in Ocean Waters