Radar Astronomy Apparatus

a radar designed for astronomical studies of the moon, planets, and large asteroids that come near the earth. The radar consists of a transmitter, which irradiates the object with radio signals; a receiver, which detects and processes the reflected echoes; recording devices; and auxiliary equipment. The characteristics of the echo signal—its power, delay time, mean spectral frequency, spectral shape, envelope, and polarization—contain information about the reflecting surface of the object. The analysis and interpretation of the data obtained by these methods are the subject of radar astronomy.

The principal indicator of the information content of the echo signal is the echo’s energy level relative to the noise energy of the receiving system, for the echo signal must be separated from the background receiver noise. In order that the signal-to-noise ratio be sufficiently high, it is necessary to use powerful transmitters, very large antennas, and cooled, low-noise receivers; in addition, the energy of the echo signal must be stored over a sufficiently long period. For weak signals, this storage time can be as long as the irradiation time and is reckoned in hours. The processing of the echo signals—that is, the separation of the signals from the underlying noise and also the frequency discrimination and the delay-time discrimination of the signals—is performed by computers and takes a length of time greater than the signal duration. Therefore, after amplification and reduction of the carrier frequency, the signal is recorded on, for example, magnetic tape before being processed.