Terrain masking

Terrain masking refers to a method of avoiding detection by radar, typically early warning radars or surface-to-air missiles. Essentially it consists of having the aircraft fly close enough to the ground that local terrain like hills and valleys block the line of sight between the aircraft and the radar, rendering the aircraft invisible.

It is important as a means of avoiding active radar by positioning the aircraft so there is natural earth hiding it from the radio waves sent from the radar system. For instance, suppose a radar transmitter is installed on a hill to monitor an area. If there was a sufficiently deep nearby valley, an aircraft flying near the bottom would not be detected because the radar would be absorbed by the top of the valley and not reach the aircraft. This concept works even on flat terrain, although only at longer ranges, due to the curvature of the earth.

Terrain masking

Terrain masking, most commonly used in aerial combat, is the act of flying at extremely low elevations upon normally hilly or mountainous terrain to minimize exposure time to anti-air weaponry.