Radar astronomy

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The radar astronomy is a method for studying the physical properties and pictorial representation of celestial bodies of our solar system . With this technique, microwaves are sent in the direction of the object to be examined by a large radio telescope or another transmitter that is capable of emitting strong, bundled microwave beams and then the reflected microwaves, i.e. the echo, are examined with a radio telescope or a network of radio telescopes , similar to an earthly radar system. Radar astronomy differs from conventional radio astronomy in that radio astronomy is a purely passive method of observing the incoming radiation from an object and radar astronomy actively emits radiation itself. In radar astronomy, a distinction is also made between pulsed and continuous microwave transmission.

history

Radar astronomical investigations began in the period between 1960 and 1975. During this time, limited observations were made with relatively weak microwave beams on Earth-like planets and near-earth objects (NEO). Today's radar astronomy has been developing since 1975.

properties

3-D model of the asteroid Cleopatra , based on radar observations ( JPL )

The strength of the radar echo signal is inversely proportional to the fourth power of the distance to the object:

The range of this technology therefore depends to a large extent on powerful transmitting and very sensitive receiving devices.

Radar technology has several advantages over other methods:

Radar astronomy provides information that would otherwise not be available. So she delivered tests for the general theory of relativity and was able to determine the length of the astronomical unit and distances to other celestial bodies of the solar system more precisely. Radar images provide information about the speed of rotation, shape and surface properties of solid bodies such as planets and asteroids.

Observed objects

Planets

The following planets were observed with the help of radar astronomy:

  • Mars - investigation of the soil for water and ice deposits. With the Mars Express space probe , the ground will be examined by radar to a depth of five kilometers.
  • Mercury - measurement of the distance to the earth , the period of rotation and coarse surface structure with greater accuracy.
  • Venus - First radar surveys in 1960. Radar astronomy made it possible for the first time to determine the duration of its rotation, first from the earth and later from probes. Its surface was also mapped using radar altimeters on space probes, of which the Magellan probe was the most successful.
  • Moon - First radar surveys in 1945. Improved value for the distance to the earth (accuracy in the range of centimeters).
  • Jupiter system
  • Saturn system

Asteroids and comets

Asteroid (53319) 1999 JM 8 : Radar data (above), the 3-D model derived from it (below), and the expected radar echo calculated from the model (middle).

The technique of radar astronomy is also used in the study of asteroids. This technique can be used to determine their position, shape, size and rotational properties. Since radar beams penetrate the ground, they can be used to better study the composition of the surface. With the help of the radar echo and its interference properties , sharp images of the object can be obtained.

Also comets have been studied by radar. Due to technical difficulties and the great distance of many comets, the number of comets observed by radar is low. The objects successfully observed using radar include the comets Hyakutake , Encke and Halley .

See also

literature

  • Bruce A. Campbell: Radar remote sensing of planetary surfaces. Cambridge University Press, Cambridge 2002, ISBN 0-521-58308-X
  • John V. Evans, Tor Hagfors: Radar astronomy. McGraw-Hill, New York 1968

Web links

Wiktionary: Radar astronomy  - explanations of meanings, word origins, synonyms, translations