Terrain-following radar

Terrain-following radar (TFR) is an aerospace technology that allows a very-low-flying aircraft to automatically maintain a relatively constant altitude above ground level. It is sometimes referred-to as ground hugging or terrain hugging flight. The term nap-of-the-earth flight may also apply but is more commonly used in relation to low-flying military helicopters, which typically do not use terrain-following radar. The technology was originally developed by Ferranti for use with the TSR-2 aircraft.