Limits to the extraction of information from multi-hop skywave radar signals

The performance of HF skywave radar systems is customarily referred to in terms of single-hop propagation, a mechanism which provides illumination of the Earth´s surface out to ranges of around 4000 kilometres. In practice, the process of ionospheric reflection often supports multiple hops, though the signals are inevitably subjected to much greater distortion and contamination. In this paper, we address the issue of adequacy of conventional models of multi-hop propagation. We formulate a detailed model which accounts for intermediate surface scattering, and obtain a representation in terms of integrals in x&oarr; - k&oarr; space. We proceed to evaluate the resulting expressions for several cases of interest. The results demonstrate that it is vital to understand the complexities of multi-hop propagation if this method of observation is to be exploited for remote sensing of the ocean at extreme ranges.