Radar horizon

The radar horizon is a critical area of performance for aircraft detection systems that is defined by the distance at which the radar beam rises enough above the Earth's surface to make detection of a target at low level impossible. It is associated with the low elevation region of performance and its geometry depends on terrain, radar height, and signal processing. This is associated with the notions of radar shadow, the clutter zone, and the clear zone.

Airborne objects can exploit the radar shadow zone and clutter zone to avoid radar detection by using a technique called nap-of-the-earth navigation.

Without taking into account the refraction through the atmosphere, the radar horizon would be the geometrical distance ${\displaystyle D_{h}}$ from the radar to the horizon only taking into account the height H of the radar above sea-level, and the radius of the earth ${\displaystyle R_{e}}$ (approximately 6.4·10³ km):

When H is small compared to ${\displaystyle R_{e}}$, this can be approximated by:

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