How do radar horizon and atmospheric ducting affect detection ranges for air and surface threats?

• A. Horizon limits radar range due to earth curvature; ducting can extend or reduce range by refracting radar waves unpredictably.
• B. Radar horizon is infinite; ducting has no effect.
• C. Ducting always increases radar range without variation.
• D. Radar horizon only affects submarines, not surface or air targets.

Answer: (A)

The key idea is that radar range is governed by geometry and atmospheric behavior, not just power or sensitivity. The Earth’s curvature creates a radio horizon, so a radar can only detect targets that rise above the line of sight from the antenna. For surface targets, their height above the water and the radar’s own height determine how far the horizon lies and thus how far you can detect them. For air targets, altitude moves the target above the horizon, increasing the detectable range, since higher aircraft are visible farther out.

Atmospheric ducting adds another layer: when temperature and humidity gradients create a refractive channel, radar waves can bend and travel along the surface or stay trapped in a duct. This can carry energy beyond the normal geometric horizon, extending detection range, but it can also cause unpredictable propagation—sometimes reducing performance or creating clutter—depending on the duct’s characteristics and path. So the actual range can be extended or reduced by ducting, rather than being fixed.

That’s why horizon limits the base range due to Earth’s curvature, and ducting can modify that range in either direction. The other statements are not accurate because horizon isn’t infinite, ducting isn’t guaranteed to always increase range, and horizon effects apply to air and surface targets, not just submarines.