Two techniques are most commonly used; shortwave systems that reflect their signals off the ionosphere for very long-range detection, and lower frequency surface wave systems that provide detection on the order of a hundred kilometres from small, conventional radar installations.
Two techniques are most commonly used; shortwave systems that reflect their signals off the ionosphere for very long-range detection, and surface wave systems which use low-frequency radio waves that due to refraction follow the curvature of the Earth to reach beyond the horizon. These systems achieve detection ranges of the order of a hundred kilometres from small, conventional radar installations.