Radio Sounding of Geospace Plasmas B. W. Reinisch University of Massachusetts, Lowell Abstract New techniques for the radio sounding of geospace plasmas are described. Advanced digital processing, including spread-spectrum and Fourier techniques, has been successfully deployed during the last decade. Similar techniques have recently been applied to space-borne sounding of the magnetosphere. It is shown that radio sounding using Doppler-sorted imaging can measure the structure and dynamics of geospace plasmas. _______________ Fisica de la Tierra, 12, 105-126, 2000.