Evaporation Duct Channel Model for Flat Sea

The evaporation duct is a natural phenomenon that occurs over large bodies of water like seas and oceans. Caused by the rapid decrease of the refractive index, evaporation ducts are important for radio communications due to their ability to enhance the signal strengths of propagated electromagnetic waves. This paper presents a channel model for evaporation ducting for a flat sea. First, basic mechanisms responsible for duct formation are overviewed. A novel way of approximating modified refractivity is proposed based on nonlinear regression analysis that allows the prediction of the evaporation duct height and strength from a set of meteorological parameters. The model also introduces the ability to use water's true relative permittivity if known. Simulation results confirm that the seawater is a good conductor, as the simulated Path Loss when water's permittivity is modelled lies within 0.1 dB of the idealised perfectly conducting surface. Simulation results are also compared to the free propagation software PETOOL. Additionally, it is concluded, that when the distance between the receiver and the transmitter is at least 40 km, the path loss is 10 to 20 dB lower compared to PETOOL due to more accurate modified refractivity profiling.