Camouflage occurs when objects are disguised so they can’t be seen easily. In their natural environment, animals have developed colours that enable them to blend into their environment, for example, a tiger’s stripes. This is mostly so they can’t be seen by other animals that might prey on and eat them.
The military uses camouflage to prevent other people seeing their operations. With new technologies using infrared1, radar2 and radio signals enabling greater ability in sensing objects, military operators have to develop new camouflage methods to avoid being detected. They have developed anti-sense strategies and methods, often using camouflage coatings or covers.
Many different ways of disguising or camouflaging metal3 objects include stealth technology (such as plasma4 clouds, radioactive5 paints and light-bending cloth) to hide objects so they cannot be sensed and therefore make them invisible to sensors used by the enemy. Mostly these technologies bend light or deflect other electromagnetic waves.
The following examples show the use of the properties of waves such as absorption, scattering and refraction6 in camouflage.
On the ground
The position of military equipment can be highly secretive. Military surveillance satellites seek out these positions. Camouflage nets and other means are used to prevent detection of the equipment.
The US Army are using Multifunctional Utility Logistics Equipment (MULEs) – unmanned remote-controlled vehicles up to 15m long and 2m wide. To make them invisible at night, they’re covered with paint that absorbs infrared waves so they can’t be seen with night goggles or other infrared sensors.
A different kind of paint is also being tested to see how it changes the wavelength7 of sensor signals used by the enemy. When the enemy sensors send out a signal, its wavelength can be changed and it can be absorbed by moisture in the air – making the target objects appear ‘invisible’.
Metamaterials are also being developed for making soldiers’ clothing. These materials bend light and any other form of electromagnetic radiation8 around whatever object it covers. Helmets may soon be equipped with lights that would blank out the soldier beneath it by electronically reading, analysing and mimicking the characteristics of the light surrounding the soldier – the soldier would be invisible.
In the air
Aircraft engineers tried to design planes that have minimal silhouettes against the daytime sky. They realised it was the shadow9 under the plane, not the colour of the underside of the plane, that made it visible during the day. They attached fluorescent lights under the fuselage and wings that pilots could dim or brighten to match the brightness of the day, thus rendering them invisible.
The idea of making planes invisible was boosted by observations made during the US space programme. They observed that a spacecraft was not sensed by radar or radio waves10 upon re-entering the atmosphere11 because a lot of friction on the surface caused it to heat12 up, creating a plasma ‘bubble’ around the craft that made it unable to be sensed by radar detectors.
A concept called plasma aerodynamics13 uses the shape of the plane and other features to ‘cloak’ or hide the plane from detection. One way of doing this could be to have an onboard device that zaps the atmosphere just in front of the aircraft, providing a cloud of plasma to fly into.
Another idea suggests using an onboard device that surrounds the craft in a plasma cloud that can absorb radar.
A third idea is to paint planes with radioisotopes that ionise14 the atmosphere surrounding the plane, placing it in a plasma sheath or glove. Electromagnetic radiation behaves differently in plasma and thus can’t be used to detect the plane.
The advantage of flying a plane in a plasma cloud is that it can reduce drag15 by 2%, making the plane fly more quickly and efficiently. A disadvantage of painting planes with radioactive material is that they can glow in the dark!
In the sea
The Swedish Navy has a Visby class of warships that are made from the same ultra-hard carbon-fibre material used in Formula One racing cars. This makes them very light and quick and reduces fuel16 consumption. These vessels have layered and textured carbon-fibre cover that absorbs radar rather than reflecting it back.
A Russian submarine uses a double-layered hull coated with rubber anti-sonar tiles to reduce the amount of sound it produces when travelling through the water.
Computer systems are also being developed to continually vary the frequency17 of vibrations given off by submarine engines so they can avoid sonar18 lock-ons and thus avoid being located.
Useful links
Watch this You Tube clip on stealth technology.
This National Geographic article How to be invisible looks at what we can learn from the way various species19 use different forms of disguise to hide from those who want to eat them – or to better ambush their prey
- infrared: Invisible electromagnetic radiation with a wavelength between approximately 0.75 micrometres and 1 millimetre. Infrared occurs between the red end of the visible light spectrum and microwaves. All things over a certain temperature (absolute zero) absorb and emit infrared radiation. Infrared radiation and observing technologies are used in many industries from medicine to finding people buried under rubble and by the military and others in night-vision goggles.
- radar: A method of detecting distant objects and determining their position, speed, or other characteristics by using very high frequency radio waves reflected from the objects’ surfaces.
- metal: Any of a category of elements that usually have a shiny surface, are generally good conductors of heat and electricity and can be melted or fused, hammered into thin sheets or drawn into wires (for example, copper).
- plasma: 1. The fourth state of matter – a gas that is ionised and consists of positive and negative ions (or particles), with no overall charge. It is affected by magnetic fields and has high electrical conductivity. 2. The colourless or pale yellow liquid in blood and lymph.
- radioactive: Giving off energy as a result of the breaking up of nuclei of atoms. Something undergoing radioactive decay, the process by which an unstable atom emits radiation.
- refraction: The bending of a wave as it passes from one medium to another. Refraction signifies a change in velocity (speed) of the wave.
- wavelength: The distance between two successive points of a wave (from one peak or crest of a wave and the next peak or crest). Usually refers to an electromagnetic wave, measured in nanometres (nm).
- radiation: Energy that is transmitted (radiates) from a source in the form of rays or waves or particles.
- shadow: A dark image produced when an object blocks rays of light from reaching a surface.
- radio waves: An electromagnetic wave having a wavelength between 1 millimetre and 30,000 metres. Radio waves are used for transmitting radio and television signals. Many celestial objects, such as pulsars, emit radio waves.
- atmosphere: 1. The layer of gas around the Earth. 2. (atm) A non-SI unit of pressure equivalent to 101.325 kPa.
- heat energy (heat): Heat energy: the transfer of energy in materials from the random movement of the particles in that material. The greater the random movement of particles the more heat energy the material has. Temperature is a measure of the heat energy of a material.
Heat: the flow of energy from a warm object to a cooler object. - aerodynamics : The study of how air flows over and through objects and the forces generated by the flow.
- ionise: The process involving either the addition or removal of electrons from an atom or molecule to form an ion. An ion carries a positive or negative charge.
- drag: Sometimes called air resistance or fluid resistance, drag refers to forces that oppose the relative motion of an object through a fluid (a liquid or gas).
- fuel: 1. A combustible substance that provides energy. 2. A body fuel such as fat, carbohydrates and protein that supplies energy for animals’ activities.
- frequency: 1. How often something occurs within a specified time. 2. The number of waves per second that pass a given point or the number of waves produced per second by a source.
- sonar: A method of detecting, locating, and determining the speed of objects through the use of reflected sound waves. A sound signal is produced, and the time it takes for the signal to reach an object and for its echo to return is used to calculate the object's distance.
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
