Investigations of irregularities in remote plasma regions by radio sounding: applications of the radio plasma imager on image

The Radio Plasma Imager (RPI) on the IMAGE mission operates like a radar by transmitting and receiving coherent electromagnetic pulses. The RPI is des igned to receive mirror-like (specular) reflections and coherent scatter re turns. Long-range echoes of electromagnetic sounder waves are reflected at remote plasma cutoffs. Thus, analyses of RPI observations will yield the pl asma parameters and distances to the remote reflection points. The RPI will employ pulse compression and spectral integration techniques, perfected in ground-based ionospheric digital sounders, in order to enhance the signal- to-noise ratio in long-range magnetospheric sounding. When plasma irregular ities exist in the remote magnetospheric plasmas being probed by the sounde r waves, echo signatures may become complicated. Experience in ionospheric sounding under such conditions indicates that sounding echo strengths can a ctually be enhanced by the presence of irregularities, and ground-based sou nding indicates that coherent detection techniques can still be employed. I n this paper we investigate the conditions that will allow coherent signals to be detected by the RPI and the signatures of scattering to be expected in the presence of multi-scale irregularities. Sounding of irregular plasma structures in the plasmasphere, plasmapause and magnetopause are also disc ussed.