Ground clutter cancellation in incoherent radars: solutions for EISCAT Svalbard radar

Incoherent scatter radars measure ionosphere parameters using modified Thom son scatter from free electrons in the target (see e.g. Hagfors, 1997). The integrated cross section of the ionospheric scatterers is extremely small and the measurements can easily be disturbed by signals returned by unwante d targets. Ground clutter signals, entering via the antenna side lobes, can render measurements at the nearest target ranges totally impossible. The E ISCAT Svalbard Radar (ESR), which started measurements in 1996, suffers fro m severe ground clutter and the ionosphere cannot be measured in any simple manner at ranges less than about 120-150 km, depending on the modulation e mployed. If the target and clutter signals have different, and clearly iden tifiable, properties then, in principle, there are always ways to eliminate the clutter. In incoherent scatter measurements, differences in the cohere nce times of the wanted and unwanted signals can be used for clutter cancel lation. The clutter cancelation must be applied to all modulations, usually alternating codes in modern experiments, used for shorter ranges. Excellen t results have been obtained at the ESR using a simple pulse-to-pulse clutt er subtraction method, but there are also other possibilities.