The New Solar Radio Observation System at Hiraiso

The Hiraiso Solar Terrestrial Research Center has been engaged in the prediction of significant disturbances in the solar terrestrial environment, and has therefore been monitoring solar radio emissions for more than 40 years. These observations had been at fixed frequencies until 1988 when a spectrograph (70-500 MHz) with a 10-m antenna was built. In FY1992 (April 1992 - March 1993) the solar radio observation system at Hiraiso was renewed. Three old antennas were replaced by new ones, and total flux measurements at 2800 MHz were started. These were in addition to the fixed frequency measurements at 200 MHz and 500 MHz. By adding two antennas, the frequency range of the spectrograph was expanded from 70-500 MHz to 25-2500 MHz. Routine observations of the sun using the new spectrograph (HiRAS: Hiraiso radio spectrograph) began late in May 1993, and daily operation is now fully automated. Everyday the antennas automatically track the sun from sunrise to sunset, and the data acquired by the HiRAS are processed by a workstation computer to produce dynamic spectrograms. An algorithm that removes interferences due to radio, television, and other artificial signals has significantly improved the signal to noise ratio of the spectrogram, thereby considerably increasing the HiRAS' ability to monitor solar radio bursts.