SuperDARN -Its importance and future possibility-
SuperDARN HF radar can emit and sweep the 16 or 20 directions of radar beam. This enables us to monitor the line of sight Doppler velocities in the wide area of ionosphere within 1 or 2 minutes. We can also monitor the global dynamics of two dimensional motion of the ionospheric plasma based on the combination of many HF radars located at high to middle latitude region. This observation network is quite powerful to study on the ionospheric dynamics from high to middle latitude and on the magnetosphere-ionosphere coupling.
Further, this kind of global observation network is very important for space weather forecast, which predicts variations of geospace environment and its effect to social infrastructure. Telecommunications, broadcasting, and navigations are affected by ionospheric disturbances. During large ionospheric disturbances, such as ionospheric storm, causes difficulties of short wave telecommunications and broadcasting, and causes large error of precise positioning using GNSS satellites. One of the major energy source which drives ionospheric disturbances are particle and electromagnetic energy penetrated from the magnetosphere to the polar ionosphere. The global distribution of this energy flow can be monitored by the combination of SuperDARN and other global observation network (magnetometer, satellite, etc.).
The enhancement of radiation belt particle causes deep dielectric charging to the satellite, which is one of the major reasons of satellite anomaly. Pc5, long period of geomagnetic pulsations (period: 150-600sec.) is one of the driver of radiation belt particle enhancement. SuperDARN is suitable for monitoring the global two dimensional distribution of Pc5 geomagnetic disturbances.
In addition, the current conditions of HF radio wave propagation can be monitored using the information of ionospheric echo and ground scatter. The area of ground scatter is an indicator for the area of possible radio wave propagation. Three dimensional ionospheric electron density distribution can be monitored for combining the model of radio wave propagation and the distribution of ground scatter.
Based on the advanced HF radar technology and the enlargement of observation network, further development of SuperDARN can be expected.
1) Multi-frequency observations
Several HF radar in SuperDARN have operated dual-frequency mode. When we got the two different frequencies of radar echo from the same ionospheric region, the accurate line-of-site Doppler velocity and electron densities at reflection point of ionosphere can be derived from these data. Further, the observation area can be expanded using simultaneous multi-frequency radar beams, since the area of radar echo is depending on the frequency of radar beam.
2) Precise elevation angle estimation based on interferometer observations
Using phase difference information obtained from two pairs of antenna aligned with line-of-site, elevation angle of radar beam reflection can be estimated with high precision.
3) Imaging radar technology
Usual HF radar has 16-20 transmitters and single receiver for a system. If we install 16-20 receivers for each antenna, we can estimate detailed distribution of ionospheric echo by synthesizing receiving signals from the receivers. This kind of technologies are being developed as imaging radar. This technology enables us to measure ionospheric disturbances by high spacial resolution.
4) Passive radar technology
SuperDARN usually operates transmitter and receiver at the same location. If we install additional receivers at other places as passive radar, we will monitor plasma drift in the ionosphere from different direction and area.
5) HF radar observation at low latitude region
To detect ionospheric variations caused by plasma bubble at geomagnetic equatorial region, Future possibility of installing HF radar at low latitude is discussed.