INVESTIGATIONS OF IONOSPHERIC RADIO-WAVE ABSORPTION PROCESSES USING IMAGING RIOMETER TECHNIQUES

The recent development of imaging riometer techniques has enabled a ra nge of new, interesting observations of the complex dynamics of aurora l and polar radio wave absorption events. These events mostly relate t o the precipitation of energetic particles, creating enhanced ionizati on in the D-region. However, E-region heating by large electric fields and F-region electron density enhancements may also-at times-be respo nsible for observable absorption effects. Observations of ionospheric radio wave absorption processes using imaging riometer techniques may provide detailed characteristics of the spatial and temporal structure s of small-scale disturbance events, velocity vectors for drifting fea tures and frequency spectra for modulated events. This presentation wi ll give a brief summary of imaging riometer techniques and a survey of existing and planned imaging riometer installations. Furthermore, the characteristics of frequently occurring absorption event types are su mmarized. In a companion paper imaging riometer observations are prese nted for some selected absorption events.