Electromagnetic sensors

The visible region

Binoculars and telescopes have changed very little. Where vibration and motion create interference, gyroscopically stabilized optics are used in surface vehicles, ships, and aircraft.

Newer in character are the image intensifiers used for nighttime detection. These devices receive the moonlight or starlight reflected from targets on a sensitive screen, amplify the image electronically, and present it at much higher light level on a small cathode-ray tube similar to that used in a television receiver. Typical of these devices is the starlight scope, resembling an oversized telescopic sight, with which riflemen can aim at night at 1,000–1,300 feet range. Artillery, tanks, helicopters, and aircraft use similar, larger devices having longer range. In aircraft the direct-viewing device is replaced by a cathode-ray tube in the instrument panel; this version is called low-light-level television.

Ordinary searchlights can often be used at night even in combat situations; but, to avoid drawing fire, invisible light, in the ultraviolet or near infrared range, can be used with appropriate viewing devices. Conventional photography, used in aerial reconnaissance and essential to long-term warning, must have high resolution despite temperature and vibration interference. To cover wide areas, panoramic cameras, scanning from side to side, record high-quality images. Frame cameras are also used, especially for mapping. At night, flares or flashing lights on aircraft are used.