Multiple scattering of HF skywave radar signals : Physics, interpretation and exploitation

HF radar signals rely on the ionosphere to achieve over-the-horizon surveillance, but this is obtained at the expense of subjecting the signals to a diverse range of scattering and modulation phenomena. Many of these effects are associated with multiple scattering, both in the ionosphere and near the earthpsilas surface. This paper reviews a variety of multiple scattering phenomena and shows how an understanding of the physics enables the radar echoes to be interpreted so as to extract information about targets and the environment. Particular attention is focussed on (i) scattering from small scale plasma irregularities, which can be used to classify propagation modes and thus improve target tracking, and (ii) scattering from the sea surface, which can be exploited for optimising radar ship detection performance as well as a range of remote sensing applications.