aerial and satellite photography, technology and science of taking still or moving-picture photographs from a camera mounted on a balloon, airplane, satellite, rocket, or spacecraft. In the 19th cent., photographers such as Thaddeus Lowe and George R. Lawrence took impressive pictures with cameras suspended in hot-air balloons or hung from kites, demonstrating both the scenic and military value of aerial photography. With the development of aviation, photogrammetry (the science of making measurements and maps from photographs) became an important tool. During World War I and subsequent conflicts, aerial photographs provided vital intelligence. Military aerial photography has now advanced to the point that the rank of a foot soldier can be determined from photographs taken from high-flying planes and satellites. Because of its military importance, much of the most sophisticated surveillance technology remains classified.

Aerial photography and satellite photography work in similar fashion. Course and speed are set before entering the area to be photographed, to ensure uniformity of speed and altitude. The result is an image of a narrow strip, which can be combined with overlapping images of neighboring strips to produce a panoramic view, commonly called a mosaic. Commercially available aerial and satellite photographs are capable of resolving objects of about 10 sq ft (1 sq m), which means that a satellite would be able to distinguish between a car and truck. Aerial photographs may be high oblique (including the horizon), low oblique (below the horizon), or vertical (perpendicular to the earth). Only the vertical may be accurately scaled for mapmaking purposes. Often a multilens camera is used to photograph one section vertically and the adjacent areas obliquely. The individual oblique exposures are then corrected, scaled, and joined to the vertical section to form one continuous photograph. By viewing two overlapping photographs through a stereoscope, a three-dimensional image of a region, or topographic map, can be obtained.

Images can also be produced at other wavelengths, such as microwave or infrared, by using a technique known as remote scanning, which measures variations in spectral reflectance rather than patterns of light and shadow. Remote scanning aids such disparate fields as archaeology, geology, forestry, highway construction, and land conservation. The best-known remote scanners are the Landsat series of satellites, which have mapped vegetation and geological formations on the earth's surface since 1972; the French SPOT series, first launched in 1986; Magellan, which used radar to map the planet Venus (1990); Lunar Prospector, which mapped the moon's surface composition and its magnetic and gravity fields (1998); Mars Global Surveyor, which engaged in a systematic mapping of Mars (1999); and Galileo, which returned pictures of Jupiter and its major moons (1995-2003).

aerial: see antenna, in electronics.

Military operations conducted by airplanes, helicopters, or other aircraft against aircraft or targets on the ground and in the water. Air warfare did not become important until World War I (1914–18). The British, French, German, Russian, and Italian armed forces had flying units, including biplanes armed with machine guns for “dogfights” with enemy fighter aircraft. Zeppelins and larger airplanes carried out bombing raids. The 1920s and '30s saw the development of the monoplane, the all-metal fuselage, and the aircraft carrier. During World War II (1939–45), the Battle of Britain was the first fought exclusively in the air, the Battle of the Coral Sea was the first between carrier-based aircraft, and the atomic bombings of Hiroshima and Nagasaki were the first use of nuclear-armed bombers. In the jet age, air power has continued to be used in strategic bombing of an enemy's home territory (as in the Vietnam War, 1965–74), destroying enemy air forces (as in the Arab-Israeli wars), attacking and defending carrier-based naval fleets (as in the Falkland Islands War, 1982), and supporting ground forces (as in the Persian Gulf War, 1990–91).

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Method of producing a sense of depth in a painting by imitating the effect of atmosphere that makes objects look paler, bluer, and hazier or less distinct in the middle and far distance. The term was coined by Leonardo da Vinci, but the technique can be seen in ancient Greco-Roman wall paintings (e.g., at Pompeii). It was discovered that dust and moisture in the atmosphere caused the scattering of light passing through it; short-wavelength light (blue) is scattered most and long-wavelength light (red) least. Italian painters in Leonardo's time used the device; it was exploited by 15th-century northern European artists and later by J.M.W. Turner.

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In zoology, one of a pair of slender, segmented sensory organs on the head of insects, myriapods (e.g, centipedes, millipedes), and crustaceans. Antennae of insects, which are movable, are believed to serve as both tactual and smell receptors; in some species, the development of elaborate antennal plumes and brushlike terminations has led to the suggestion that they also serve for hearing. Evidence supports this idea only for the mosquito, whose antennae are attached to specialized structures stimulated by vibrations of the antennal shaft. In social insects (e.g., ants), antennae movements may serve as communication.

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