A method based on measuring the electric polarization of a wave has been devised to measure the direction and wave mode of the echoes that are detected by a satellite radio sounder in the Earth's magnetosphere. Except for directions that are almost exactly perpendicular to the magnetic field, this method is found to work at frequencies above about 20 kHz with an angular error of less than about 1¿. A second method that is based on measuring the Faraday rotation of the axis of polarization has also been devised to measure the echo direction when the ordinary and extraordinary echoes that are produced by a radio sounder overlap to produce an elliptically or linearly polarized wave. These two methods will then be used to analyze the measurements of the Image radio sounder that is scheduled to be launched in the year 2000, as described in the feasibility analysis for the Image sounder that was published in 1995. ¿ 1999 American Geophysical Union