The radar astronomy is a method for investigating the physical properties and pictorial representation of celestial bodies in our solar system. This technique uses microwaves from a radio telescope or another transmitter, capable of emitting strong collimated microwave beams emitted in the direction of the examined object and then with a radio telescope or network of radio telescopes, the reflected microwaves, thus analyzing the echo, similar to an earth-based radar system. Radar astronomy differs from conventional radio astronomy is that radio astronomy is a passive method of observation of the incoming radiation of an object and radar astronomy active itself emits radiation. In the radar astronomy is additionally distinguished between pulsed and continuous microwave transmission.
The beginnings radarastronomischer studies are in the period 1960-1975 at this time. Observations with relatively weak microwave radiation to the Earth-like planet and near-Earth objects ( NEOs) have been made to a limited extent. Since 1975 that evolved into today's radar astronomy.
The strength of the radar echo signal is proportional to the fourth root of the distance to the object:
The range of this technique thus depends heavily on strong transmitter and very sensitive receiver devices.
Radar technology has several advantages over other methods:
- Controlling the characteristics of the signal (that is, the modulation frequency and strength of the shaft and its polarization)
- Spatial resolution of objects (especially asteroids )
- Doppler shift measurements,
- Penetration into opaque materials the surface,
By Radar Astronomy obtained information that would otherwise not be available otherwise. So they gave tests for general relativity and could determine the length of the Astronomical Unit and distances to other celestial bodies in the solar system in more detail. Radar images provide information on the speed of rotation, shape and surface tilt properties of solid bodies, such as planets and asteroids.
The following planets have been observed by means of radar astronomy:
- Mars - investigation of the soil to water and ice deposits. With the world 's Mars Express spacecraft, the soil is to be examined to a depth of five km by radar.
- Mercury - measuring the distance to the Earth, the rotation period and rough surface structure with greater accuracy.
- Venus -. First radar studies in 1960 by the radar astronomy was its period of rotation is first determined by the earth and later of probes from the first time. With the help of radar altimeters on space probes, of which the Magellan probe was the most successful, and its surface was mapped.
- Moon - First radar studies in 1945 Improved value for the distance to Earth ( accuracy in the range of centimeters ). .
- Jupiter system
- Saturn system
Asteroids and comets
The technique of radar astronomy is also used in the study of asteroids. With this technique, one can determine their position, shape, size and rotation properties. Since radar beams can penetrate the soil to better study with their help, the composition of the surface. With the help of radar echoes and its interference properties can win sharp images of the object.
Comets have been investigated by means of radar. Due to technical difficulties and the great distance of many comets, the number of comets observed by radar, however, is low. Among the successfully observed by means of radar objects include the comet Hyakutake, Halley and Encke.