Multifrequency RF-measurements and characterisation of propagation conditions in the maritime boundary layer

In the maritime boundary layer, air-sea interaction processes have an important impact on radar propagation. The radar range performance near the sea surface depends on meteorological and sea surface conditions. Strong gradients of humidity and temperature close to the air-water interface are most often the reason for propagation effects such as ducting. For ship borne radars the evaporation duct is the dominant propagation mechanism affecting the maximum detection range. Ducting can also increase sea clutter return within and beyond the geometric horizon. Duct characteristics (duct heights, duct structures, duct formation behavior, duct existence, duct vertical and horizontal variability) depend on climatic zones and regional peculiarities. In this contribution we report on a RF propagation experiment performed in the North Sea close to the Island of Sylt. One focus is given to the derivation of the modified refractive index profiles deduced from a multitude of sensors including tethersondes, catamaran, and ship-borne sensors.