Nap-of-the-earth (abbreviated
NOE) is very low-level type of
flightFlight is the process by which an object moves either through the air, or movement beyond earth's atmosphere , by aerodynamically generating lift, propulsive thrust or aerostatically using buoyancy, or by simple ballistic movement.-Buoyant flight:Humans, although not apparently other animals, have...
course used to avoid detection and attack by an enemy when in a high-threat environment.
Geographical features are used as cover, exploiting valleys and folds in the ground by flying in them rather than over them to avoid 'skylining' to an enemy and to keep below radar cover. Other terms such as 'ground-hugging', '
terrain maskingTerrain mask is a term used in both aviation and GPS equipment.A terrain mask refers to the natural curvature of the earth. 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...
', or 'flying under the
radarRadar is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for RAdio Detection And...
' are also used.
NOE is used to minimise detection by hostile aircraft, by AWACS surveillance and control systems, by ground-based radar or by the actual targets of the attack (such as when setting up a helicopter strike against an armored force).
A high-flying aircraft would be detected by defense systems at long range, allowing an air defense system time to react, alert
SAMA Surface to Air Missile or ground-to-air missile is a missile designed to be launched from the ground to destroy aircraft. It is a type of anti-aircraft system....
and AAA systems and scramble fighter (Air Defence) aircraft.
Nap-of-the-earth (abbreviated
NOE) is very low-level type of
flightFlight is the process by which an object moves either through the air, or movement beyond earth's atmosphere , by aerodynamically generating lift, propulsive thrust or aerostatically using buoyancy, or by simple ballistic movement.-Buoyant flight:Humans, although not apparently other animals, have...
course used to avoid detection and attack by an enemy when in a high-threat environment.
Geographical features are used as cover, exploiting valleys and folds in the ground by flying in them rather than over them to avoid 'skylining' to an enemy and to keep below radar cover. Other terms such as 'ground-hugging', '
terrain maskingTerrain mask is a term used in both aviation and GPS equipment.A terrain mask refers to the natural curvature of the earth. 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...
', or 'flying under the
radarRadar is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for RAdio Detection And...
' are also used.
Purpose
NOE is used to minimise detection by hostile aircraft, by AWACS surveillance and control systems, by ground-based radar or by the actual targets of the attack (such as when setting up a helicopter strike against an armored force).
A high-flying aircraft would be detected by defense systems at long range, allowing an air defense system time to react, alert
SAMA Surface to Air Missile or ground-to-air missile is a missile designed to be launched from the ground to destroy aircraft. It is a type of anti-aircraft system....
and AAA systems and scramble fighter (Air Defence) aircraft. Using NOE flight, the approach may be undetected, the aircraft "pops up" to attack the target and then turns to escape before the enemy can respond.
Doppler radarDoppler radar is radar that makes use of the doppler effect to produce data about objects at a distance. It does this by beaming a microwave signal towards a desired target and listening for its reflection, then analyzing how the original signal has been altered by the object that reflected it...
has the potential to detect NOE flight but the incoming aircraft has to be within radar range in the first place and low flying minimises this possibility due to the effect of
terrain maskingTerrain mask is a term used in both aviation and GPS equipment.A terrain mask refers to the natural curvature of the earth. 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...
.
Sensors for NOE
Most NOE flying is done during the day using visual reference by pilots who are experienced in low flying. Data from a
radar altimeterA radar altimeter, radio altimeter, low range radio altimeter or simply RA measures altitude above the terrain presently beneath an aircraft or spacecraft...
or
terrain-following radarTerrain-following radar 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...
system is also used, the latter enabling low flying in adverse weather where it would not be possible by visual reference and manual pilot control. At night, intensifier systems or infra-red can be used. "Night Vision Goggles" (NVGs) are visual intensifiers working in the near-IR area at a wavelength of about 1 micrometre and
Forward-Looking Infra RedForward looking infrared is an imaging technology that senses infrared radiation.Since FLIRs use detection of thermal energy to create the "picture" assembled for the video output, they can be used to help pilots and drivers steer their vehicles at night, and in fog, or detect warm objects against...
(FLIR, or Thermal Imaging (TI)) works at about 10 micrometres. NVGs require some ambient light such as from the moon or ground lights while FLIR is entirely passive and produces a picture based on the heat distribution of the area being observed.
Helicopter NOE flying
The lowest NOE flying is by
helicopterA helicopter is an aircraft that is lifted and propelled by one or more horizontal rotors, each rotor consisting of two or more rotor blades. Helicopters are classified as rotorcraft or rotary-wing aircraft to distinguish them from fixed-wing aircraft because the helicopter achieves lift with the...
s because they have lower speeds and more maneuverability than fixed-wing aircraft, particularly fast-jets. Helicopters can fly at 'tree-top' levels or even below the height of surrounding trees where there are clear areas (such as in river gullies), flying under wires (such as electricity cables) rather than over them. Attack helicopters can hide behind trees or buildings, 'popping up' just enough to use their (rotor mast-mounted) radar or other sensors and then minimally exposing themselves to launch weapons. Escape can then be made by further NOE flying. The altitude is different dependent on the area of operations, and is related to understory canopy layer (<15m/50ft) or low building, tree canopy layer of less than 45m (147ft), presence of tall buildings or concrete pylons with heights of up to 25 metres (76ft) international standard, or emergent tree layer canopy and lattice steel electricity pylon to 100m (328ft) being present in the area. Over populated areas an altitude of 500 feet AGL applies where transmission towers of 500ft are in use, these first installed in the 1940s in the northern hemisphere.
Heights Above Ground Level
Heights Above Ground Level (AGL) in NOE and low flying generally vary with the aircraft speed, aircraft maneuverability and the ruggedness of the terrain. Helicopters are capable of flying down to a few feet below the skids or wheels. Fast jets are more constrained and at a typical low-flying speed of 450 knots (800 km/h), 200 feet (60 m) is not unusual and 50 feet (15 m) is possible in relatively flat terrain. Power wires are a danger to all aircraft flying at low level and 'wire strikes' are not uncommon. Special maps are produced that plot the routes of these wires but these are difficult to keep up-to-date, especially for foreign/enemy countries. Pilots are trained to scan for the pylons or power-poles that support these wires, because they can be seen at a distance where the wires themselves cannot.