超视距观察是一项昂贵的工程。尤其是需要探测普通微波雷达无法探测的舰船、低空飞行的飞机和导弹。虽然,首批实用系统还正在建造中,但超视距(OTH)雷达已为许多人所熟知,尤其是使用高频天波的远程超视距雷达。这些系统利用电离层反身信号来探测1000～3000km之间的舰船和飞机目标。部分无线电能被目标散射,并再次经过电离层返回雷达接收机。 Over-the-horizon observation is an expensive project. In particular, it is necessary to detect ships that can not be detected by ordinary microwave radars, aircraft and missiles flying at low altitudes. Although the first practical systems are still under construction, OTH radars are well known to many, especially remote over-the-horizon radars that use HF sky waves. These systems use ionospheric reflex signals to detect ships and aircraft targets between 1000 and 3000 km. Part of the radio energy is scattered by the target and back again through the ionosphere to the radar receiver.