Radar horizon

Distance at which ground targets are hidden Radar horizon. The radar horizon is a critical area of performance for aircraft detection systems, defined by the distance at which the radar beam rises enough above the Earth's surface to make detection of a target at the lowest level possible. It is associated with the low elevation region of performance, and its geometry depends on terrain, radar height, and signal processing. This concept 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. Definition Without taking into account the refraction through the atmosphere, the radar horizon would be the geometrical distance D h {\displaystyle D_{h}} from the radar to the horizon only taking into account the height H {\displaystyle H} of the radar above sea-level, and the radius of the earth R e {\displaystyle R_{e}} (approximately 6.4·103 km): D h = 2 × H × R e + H 2 {\displaystyle D_{h}={\sqrt {2\times H\times R_{e}+H^{2}}}} When H is small compared to R e {\displaystyle R_{e}} , this can be approximated by