Radar Sounders
type: Concept

RADAR
in scheme: instruments
definition: Radar is an acronym for "radio detection and ranging." A radar system usually operates in the ultra-high-frequency (UHF) or microwave part of the radio-frequency (RF) spectrum, and is used to detect the position and/or movement of objects. Radar can track storm systems, because precipitation reflects electromagnetic fields at certain frequencies. Radar can also render precise maps. Radar systems are widely used in air-traffic control, aircraft navigation, and marine navigation. High-power radar, using large dish antennas, has been used to measure distances to the moon, other planets, asteroids, and artificial satellites. From unmanned space probes, radar has been used to map Venus, whose surface is obscured at visible wavelengths by a thick layer of clouds. Radar has been employed by NASA (the U.S. National Aeronautics and Space Administration) to make highly detailed topographical maps of the earth's surface as well. Most radar systems determine position in two dimensions: azimuth (compass bearing) and radius (distance). The display is in polar coordinates. A rotating antenna transmits RF pulses at defined intervals. The delay between a transmitted pulse and the echo, or return pulse, determines the radial position of the plotted point(s) for each azimuth direction on the display. The greater the echo delay from a particular object in space, the farther from the display center its point appears. The maximum range of a UHF or microwave radar system depends on the height of the antenna above average terrain, the topography of the surface in the region, the atmospheric conditions in the region, and in some cases the level of radio background noise. Radar is known to the general public for its use by law enforcement in determining the speeds of motor vehicles. This type of radar does not display the exact position of an object, but determines its radial speed vector from the Doppler effect. A radar detector, which consists of a simple UHF/microwave broadband receiver, …
type: Concept