Nap of the Earth
NAP OF THE EARTH, or NOE, is a Vietnam War-era term for very low-level flight, particularly of helicopters. The concept behind this type of flying is that a pilot guides his or her craft as close to the Earth's surface as terrain, vegetation, and other obstructions will allow and maintains that low altitude while approaching a chosen target or transiting an area. This flight technique becomes a tactic for surprise and survival as the aircraft comes into and passes out of a ground observer's field of vision before an enemy can target and engage the aircraft. It also has the advantage of getting the aircraft below acquisition radar detection envelopes and blending in with the ground clutter provided by vegetation and intervening topography. This type of flight is included in the more inclusive term terrain flight or TERF.
An official Department of Defense definition is: “Flight close to the Earth's surface during which airspeed, height, and/or altitude are adapted to the contours and cover of the ground in order to avoid enemy detection and fire.”