Refraction (electromagnetic)

Electromagnetic refraction is the bending of radar and light rays as they pass through air of changing density, which extends the radar and visual horizon beyond the geometric line of sight. Under standard atmosphere the radar horizon is about 1.07 times the square root of antenna height in metres, giving a range slightly greater than the optical horizon because longer wavelengths bend more. Anomalous conditions distort this: super-refraction and ducting from a temperature inversion stretch detection range and can show targets far past normal limits, while sub-refraction shortens it. The navigator allows for these effects when judging radar range and the rising or dipping distance of lights.