A.L. Dzvonkovskaya, L.I. Dzvonkovsky

Long distance surveillance using HFSWR is a developing technology, which has already shown its capabilities to detect ships and aircrafts, to collect data about the ocean environment remotely. The working principle of HFSWR is based on the diffraction of HF radio wave with vertical polarization along the earth surface. Hereby the electrical properties of the earth surface, i.e. conductivity  and relative electric permittivity , have an important role for HFSWR operation. The sea surface is a good conductor versus the land that has weak conductive properties for HF band. There are different scenarios of HF surface wave propagation depending on the region and HFSWR coverage. It is necessary to propose an adequate propagation model in order to estimate the signal attenuation along the path for different working frequencies. The environment is modeled as spherical Earth with finite soil conductivity, rough surface and changing refraction conditions along it. The final accurate solution hasn-t been found yet and several approximate solutions are available. The difficulty in HF attenuation estimation corresponds to the inhomogeneous paths consisted of sea land patches between the HFSWR and the target. Exiting theoretical formulas are complicated to realize therefore the Millington-s empirical technique [12] seems to be simple and gives satisfactory results compared to theory. This technique is used in CCIR Rec. 368-8 and includes the problems of homogeneous and mixed HF surface propagation paths. For homogeneous paths along the surface the Recommendations show the dependencies, according to them one can estimate the electric field strength of vertical polarized waves for different distances, working frequencies, conductivity and relative permittivity of earth surface. Nevertheless the use of graphical data from Recommendations is not convenient for the HFSWR permanently choosing the operating frequencies with minimal active interference levels to adapt to complicated electromagnetic environment. To search for HFSWR locations in the specified regions it is important to estimate the radar propagation losses to fulfill the technical maintenance specification. Such estimation is necessary in real time especially during the HFSWR operation along the inhomogeneous paths. To overcome this problem there is a necessity to develop an interface-friendly software tool to estimate radar path losses. Inhomogeneous propagation paths are considered for HFSWR. The radar paths include different sets of homogeneous patches with different electrical properties of sea, land, and oil spills. The propagation path losses are estimated taking into account the sea state conditions