Terrain masking
![Areas in red indicate where an aircraft would be masked by the terrain](/Images/godic/202502/15/Terrain_Masking.svg0029.png")
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.