Attenuation factor for X- and Ka-band near sea surface

The results of experimental investigations concerning the attenuation factor of electromagnetic field in X- and Ka-radiowave band for propagation at grazing angles near sea surface have been analyzed. Attention is paid to the statistical parameters of the field in the space area that corresponds to the penumbra in the standard refraction conditions. The phenomena in illuminated zone have been investigated and the applicability of the interference field description for practical calculations is proved. At the same time the radar monitoring realized by ship and coastal radar and focused on sea waves and objects elevated slightly above the water surface, such as floating ice, logs or reefs has to be realized in the conditions of operating in the penumbra. As experimental researches and the theoretical analyses results show, both interference model and the diffraction phenomenon on the Earth spherical surface can not be used for the description of the millimeter and centimeter waves in this zone. A series of the phenomena discovered in the penumbra experimentally, in particular, signal fluctuation spectra features, can explain the field at low height above the surface as a result of a diffraction on the wave crests, that are simulated as opaque half-planes in the calculation. In the submitted paper the characteristics of the attenuation factor that are needed for the radar set power computing are discussed: its mean values, distribution laws as the functions of the range and the elevation of the observation point above the sea surface