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Ionospheric Observation
The National Institute of Information and Communications Technology conducts routine observation of the ionosphere from areas throughout Japan. At the Okinawa Electromagnetic technology Center's Ogimi Ionospheric Observation Facility located at the southern end of Japan, ionospheric observations are performed every 15 minutes. These observation data are then transferred to NICT headquarters (in Koganei, Tokyo), the site of the World Data Center for Ionosphere C2.

Q. What is the "ionosphere"

A. The ionosphere is a region of the earth's atmosphere above an altitude of approximately 70 km, where atoms and molecules in the atmosphere are transformed into electrons and ions due to the effect of solar ultraviolet and x-ray radiation. High-frequency radio waves (at frequencies of 3-30 MHz) are reflected by this region. International communications and broadcasts that employ HF radio waves are affected by the ionosphere, and it is therefore important that we be able to monitor this region of the atmosphere.

Q. How do you monitor the ionosphere?

A. HF radio waves either pass through or are reflected by the ionosphere, depending on their frequencies. Those waves that are reflected by the ionosphere are reflected at different altitudes (again depending on the frequency of the waves); moreover, the relationship between frequency and altitude is constantly changing. The altitude at which each radio frequency is reflected can be determined by emitting radio waves from the ground toward the sky at various frequencies and measuring the intensity and the time delay of the reflected signal. Examples of such ionospheric data (in the form of "ionograms") can be found at the website below, where you can also obtain up-to-date information on the state of the ionosphere over Japan.


Q. Where is ionospheric observation conducted?

A. Ionospheric observation in Japan is carried out every 15 minutes at the NICT headquarters, at the Wakkanai Radio Observatory, at the Yamagawa Radio Observatory, and at the Okinawa Electromagnetic Technology Center (NICT Okinawa). In addition, similar ionospheric observations are presently conducted from 130 locations around the world; collected data are then sent to the World Data Center for Ionosphere for use by researchers and the general public as resource materials for research.

For more details concerning ionospheric observation, see the following page.


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