PURPOSE:To eliminate the standard noise source of each channel, to reduce an external size and weight, and also to always execute an observation on a track by using only a multi-channel low temperature noise source by a radiation terminal and utilizing a calibrating straight line. CONSTITUTION:An observing signal from an antenna 1 which is loaded on a flying object such as an artificial satellite, and receives the observing signal is distributed to plural channels by a demultiplexer 3. A low temperature noise temperature from a radiation cooling terminal 11 used for a low temperature noise source covered with a thermal insulator 12 is distributed to plural channels by a demultiplexer 4. Also, an attenuator 13 raises the low temperature noise temperature distributed from the terminal 11, and its output is distributed to plural channels by a demultiplexer 14. A switch 7 switches the antenna 1 and the terminal 11, and a switch 8 switches the antenna 1 or the terminal 11, and the demultiplexer 14 for outputting a high temperature noise temperature raised by the attenuator 13. A receiver 10 amplifies and detects an input noise temperature.
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