An Electrostatic-Wave Topside Sounder

An electrostatic-wave topside sounder has been flown to study electron plasma resonances. Unique features of this sounder are the preservation of data spectra, a frequency synthesizer, and a gain-change mechanism. Preservation of the spectra provided frequency information with a resolution of a few hundred hertz by use of a fast Fourier transform while the synthesizer provided the necessary frequency stability. The gain-change mechanism provided information on the strength of the resonances. Resulting data support the electrostatic-wave echo theory of topside resonances.