A new radar method for the estimation of the electron number density, electron temperature, and ion temperature in a plasma which is modified by a strong electromagnetic wave is described. The method relies on the possibility of obtaining high resolution plasma line spectra containing the main parametric decay lines together with a few parametric decay cascade lines. Assuming that simple, linear wave kinematical arguments are valid it is shown that the frequency shifts between these lines under certain circumstances can be used to determine three of the most important plasma parameters in the nonlinear interaction region. ¿ American Geophysical Union 1989