Whistler-mode wave-injection experiments in the plasmasphere with a radio sounder V.S. Sonwalkar, X. Chen, J. Harikumar, D.L. Carpenter and T.F. Bell Whistler-mode wave-injection experiments with a high-altitude radio sounder offer an opportunity to greatly extend the observing power of satellites such as imager for magnetopause-to-aurora global exploration (IMAGE) when the satellite is within or near the plasmasphere or at low altitudes over the polar regions. We use as an example the radio plasma imager (RPI) instrument on IMAGE, which includes crossed 500-m electric antennas in the spin plane and a 20-m antenna along the spin axis (for reception only). The 500-m antennas approach a half-wavelength at whistler-mode frequencies in the 3-30kHz range and should have a radiation efficiency of 1-10%. The wave power within ~100km of the transmitter should be greater than that produced by wave injection from the ground-based very low-frequency (VLF) transmitter at Siple, Antarctica, thus making possible experiments on wave-particle energy and momentum exchange. We use ray tracings along a sample IMAGE orbit (polar, apogee ~8RE) to show the conditions under which transmitted signals may return to the satellite as echoes, following reflection, or be observed by satellites of opportunity, such as EXOS-D. We find that ground reception of transmitted signals should be possible as a result of a linear mode conversion process in regions of ionospheric irregularities. We discuss the determination of wave-normal angles of returning signals, which will aid in identifying the signal path and obtaining information on plasma boundaries and irregularities. The science topics that may be addressed include: (1) investigation of the nonlinear process by which weak coherent waves excite VLF emissions; (2) probing plasmaspheric density structure, including plasmaspheric density cavities, field aligned waveducts, density irregularities in the plasmapause region, and the ionospheric density structure where conversion of whistler-mode wave energy to quasi-electrostatic lower hybrid (LHR) waves (and vice versa) can take place. _______________ Journal of Atmospheric and Solar-Terrestrial Physics, Vol. 63 (11) pp. 1199-1216, 2001