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Millimetre wave scattering by sea foam using split-step fourier transform

Summary form only given. This work focuses on developing a theoretical model for evaluating millimetre wave scattering by sea surface and sea foam. Numerous methods such as radiative transfer theory, quasi-crystalline approximation method, Monte-Carlo and other hybrid methods are available [1, 2]. These methods were developed by assuming the macroscopic properties of seafoam. At moderate wind speed, this assumption is acceptable since the scattering is negligible, while absorption play a significant role. However, under strong winds, sea surface roughness increases and breaking waves take place. These effects highly contributes to induce a significant scattering process leading to high transmission losses. In this case modelling sea foam only through macroscopic properties is not appropriate. A new approach of modelling sea foam is proposed to account for the optical properties at microscopic level such as foam layer thickness, foam void fraction, bubble radius, bubble size distribution and bubble shape. The bubble size distribution and bubble radius are evaluated by inverse cumulative error function using the Newton Raphson's method. A three dimensional sphere packing approach is applied for filling the bubbles in the domain [3]. The domain could be a cube, cuboid, prism or cylinder, and the packing is done such that no two bubbles overlapped. The random close packing method of spheres is used for the irregular arrangement of spheres so that they are densely packed [3] with the bubble volume fraction of 64% while the space within the cube or other domain geometry is 36% for maximum packing density. Finally, the Split-Step Fourier solution of the Parabolic Wave Equation (PWE) [4] is used to evaluate the refractive and the diffractive effects of the scattered field.